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# What's New in Python 2.7
作者A.M. Kuchling (amk at amk.ca)
This article explains the new features in Python 2.7. Python 2.7 was released on July 3, 2010.
Numeric handling has been improved in many ways, for both floating-point numbers and for the [`Decimal`](../library/decimal.xhtml#decimal.Decimal "decimal.Decimal") class. There are some useful additions to the standard library, such as a greatly enhanced [`unittest`](../library/unittest.xhtml#module-unittest "unittest: Unit testing framework for Python.") module, the [`argparse`](../library/argparse.xhtml#module-argparse "argparse: Command-line option and argument parsing library.") module for parsing command-line options, convenient [`OrderedDict`](../library/collections.xhtml#collections.OrderedDict "collections.OrderedDict")and [`Counter`](../library/collections.xhtml#collections.Counter "collections.Counter") classes in the [`collections`](../library/collections.xhtml#module-collections "collections: Container datatypes") module, and many other improvements.
Python 2.7 is planned to be the last of the 2.x releases, so we worked on making it a good release for the long term. To help with porting to Python 3, several new features from the Python 3.x series have been included in 2.7.
This article doesn't attempt to provide a complete specification of the new features, but instead provides a convenient overview. For full details, you should refer to the documentation for Python 2.7 at <https://docs.python.org>. If you want to understand the rationale for the design and implementation, refer to the PEP for a particular new feature or the issue on <https://bugs.python.org> in which a change was discussed. Whenever possible, "What's New in Python" links to the bug/patch item for each change.
## The Future for Python 2.x
Python 2.7 is the last major release in the 2.x series, as the Python maintainers have shifted the focus of their new feature development efforts to the Python 3.x series. This means that while Python 2 continues to receive bug fixes, and to be updated to build correctly on new hardware and versions of supported operated systems, there will be no new full feature releases for the language or standard library.
However, while there is a large common subset between Python 2.7 and Python 3, and many of the changes involved in migrating to that common subset, or directly to Python 3, can be safely automated, some other changes (notably those associated with Unicode handling) may require careful consideration, and preferably robust automated regression test suites, to migrate effectively.
This means that Python 2.7 will remain in place for a long time, providing a stable and supported base platform for production systems that have not yet been ported to Python 3. The full expected lifecycle of the Python 2.7 series is detailed in [**PEP 373**](https://www.python.org/dev/peps/pep-0373) \[https://www.python.org/dev/peps/pep-0373\].
Some key consequences of the long-term significance of 2.7 are:
- As noted above, the 2.7 release has a much longer period of maintenance when compared to earlier 2.x versions. Python 2.7 is currently expected to remain supported by the core development team (receiving security updates and other bug fixes) until at least 2020 (10 years after its initial release, compared to the more typical support period of 18--24 months).
- As the Python 2.7 standard library ages, making effective use of the Python Package Index (either directly or via a redistributor) becomes more important for Python 2 users. In addition to a wide variety of third party packages for various tasks, the available packages include backports of new modules and features from the Python 3 standard library that are compatible with Python 2, as well as various tools and libraries that can make it easier to migrate to Python 3. The [Python Packaging User Guide](https://packaging.python.org) \[https://packaging.python.org\] provides guidance on downloading and installing software from the Python Package Index.
- While the preferred approach to enhancing Python 2 is now the publication of new packages on the Python Package Index, this approach doesn't necessarily work in all cases, especially those related to network security. In exceptional cases that cannot be handled adequately by publishing new or updated packages on PyPI, the Python Enhancement Proposal process may be used to make the case for adding new features directly to the Python 2 standard library. Any such additions, and the maintenance releases where they were added, will be noted in the [New Features Added to Python 2.7 Maintenance Releases](#py27-maintenance-enhancements) section below.
For projects wishing to migrate from Python 2 to Python 3, or for library and framework developers wishing to support users on both Python 2 and Python 3, there are a variety of tools and guides available to help decide on a suitable approach and manage some of the technical details involved. The recommended starting point is the [將 Python 2 代碼遷移到 Python 3](../howto/pyporting.xhtml#pyporting-howto) HOWTO guide.
## Changes to the Handling of Deprecation Warnings
For Python 2.7, a policy decision was made to silence warnings only of interest to developers by default. [`DeprecationWarning`](../library/exceptions.xhtml#DeprecationWarning "DeprecationWarning") and its descendants are now ignored unless otherwise requested, preventing users from seeing warnings triggered by an application. This change was also made in the branch that became Python 3.2. (Discussed on stdlib-sig and carried out in [bpo-7319](https://bugs.python.org/issue7319) \[https://bugs.python.org/issue7319\].)
In previous releases, [`DeprecationWarning`](../library/exceptions.xhtml#DeprecationWarning "DeprecationWarning") messages were enabled by default, providing Python developers with a clear indication of where their code may break in a future major version of Python.
However, there are increasingly many users of Python-based applications who are not directly involved in the development of those applications. [`DeprecationWarning`](../library/exceptions.xhtml#DeprecationWarning "DeprecationWarning") messages are irrelevant to such users, making them worry about an application that's actually working correctly and burdening application developers with responding to these concerns.
You can re-enable display of [`DeprecationWarning`](../library/exceptions.xhtml#DeprecationWarning "DeprecationWarning") messages by running Python with the [`-Wdefault`](../using/cmdline.xhtml#cmdoption-w) (short form: [`-Wd`](../using/cmdline.xhtml#cmdoption-w)) switch, or by setting the [`PYTHONWARNINGS`](../using/cmdline.xhtml#envvar-PYTHONWARNINGS)environment variable to `"default"` (or `"d"`) before running Python. Python code can also re-enable them by calling `warnings.simplefilter('default')`.
The `unittest` module also automatically reenables deprecation warnings when running tests.
## Python 3.1 Features
Much as Python 2.6 incorporated features from Python 3.0, version 2.7 incorporates some of the new features in Python 3.1. The 2.x series continues to provide tools for migrating to the 3.x series.
A partial list of 3.1 features that were backported to 2.7:
- The syntax for set literals (`{1,2,3}` is a mutable set).
- Dictionary and set comprehensions (`{i: i*2 for i in range(3)}`).
- Multiple context managers in a single [`with`](../reference/compound_stmts.xhtml#with) statement.
- A new version of the [`io`](../library/io.xhtml#module-io "io: Core tools for working with streams.") library, rewritten in C for performance.
- The ordered-dictionary type described in [PEP 372: Adding an Ordered Dictionary to collections](#pep-0372).
- The new `","` format specifier described in [PEP 378: Format Specifier for Thousands Separator](#pep-0378).
- The [`memoryview`](../library/stdtypes.xhtml#memoryview "memoryview") object.
- A small subset of the [`importlib`](../library/importlib.xhtml#module-importlib "importlib: The implementation of the import machinery.") module, [described below](#importlib-section).
- The [`repr()`](../library/functions.xhtml#repr "repr") of a float `x` is shorter in many cases: it's now based on the shortest decimal string that's guaranteed to round back to `x`. As in previous versions of Python, it's guaranteed that `float(repr(x))` recovers `x`.
- Float-to-string and string-to-float conversions are correctly rounded. The [`round()`](../library/functions.xhtml#round "round") function is also now correctly rounded.
- The [`PyCapsule`](../c-api/capsule.xhtml#c.PyCapsule "PyCapsule") type, used to provide a C API for extension modules.
- The [`PyLong_AsLongAndOverflow()`](../c-api/long.xhtml#c.PyLong_AsLongAndOverflow "PyLong_AsLongAndOverflow") C API function.
Other new Python3-mode warnings include:
- `operator.isCallable()` and `operator.sequenceIncludes()`, which are not supported in 3.x, now trigger warnings.
- The `-3` switch now automatically enables the `-Qwarn` switch that causes warnings about using classic division with integers and long integers.
## PEP 372: Adding an Ordered Dictionary to collections
Regular Python dictionaries iterate over key/value pairs in arbitrary order. Over the years, a number of authors have written alternative implementations that remember the order that the keys were originally inserted. Based on the experiences from those implementations, 2.7 introduces a new [`OrderedDict`](../library/collections.xhtml#collections.OrderedDict "collections.OrderedDict") class in the [`collections`](../library/collections.xhtml#module-collections "collections: Container datatypes") module.
The [`OrderedDict`](../library/collections.xhtml#collections.OrderedDict "collections.OrderedDict") API provides the same interface as regular dictionaries but iterates over keys and values in a guaranteed order depending on when a key was first inserted:
```
>>> from collections import OrderedDict
>>> d = OrderedDict([('first', 1),
... ('second', 2),
... ('third', 3)])
>>> d.items()
[('first', 1), ('second', 2), ('third', 3)]
```
If a new entry overwrites an existing entry, the original insertion position is left unchanged:
```
>>> d['second'] = 4
>>> d.items()
[('first', 1), ('second', 4), ('third', 3)]
```
Deleting an entry and reinserting it will move it to the end:
```
>>> del d['second']
>>> d['second'] = 5
>>> d.items()
[('first', 1), ('third', 3), ('second', 5)]
```
The [`popitem()`](../library/collections.xhtml#collections.OrderedDict.popitem "collections.OrderedDict.popitem") method has an optional *last*argument that defaults to `True`. If *last* is true, the most recently added key is returned and removed; if it's false, the oldest key is selected:
```
>>> od = OrderedDict([(x,0) for x in range(20)])
>>> od.popitem()
(19, 0)
>>> od.popitem()
(18, 0)
>>> od.popitem(last=False)
(0, 0)
>>> od.popitem(last=False)
(1, 0)
```
Comparing two ordered dictionaries checks both the keys and values, and requires that the insertion order was the same:
```
>>> od1 = OrderedDict([('first', 1),
... ('second', 2),
... ('third', 3)])
>>> od2 = OrderedDict([('third', 3),
... ('first', 1),
... ('second', 2)])
>>> od1 == od2
False
>>> # Move 'third' key to the end
>>> del od2['third']; od2['third'] = 3
>>> od1 == od2
True
```
Comparing an [`OrderedDict`](../library/collections.xhtml#collections.OrderedDict "collections.OrderedDict") with a regular dictionary ignores the insertion order and just compares the keys and values.
How does the [`OrderedDict`](../library/collections.xhtml#collections.OrderedDict "collections.OrderedDict") work? It maintains a doubly-linked list of keys, appending new keys to the list as they're inserted. A secondary dictionary maps keys to their corresponding list node, so deletion doesn't have to traverse the entire linked list and therefore remains O(1).
The standard library now supports use of ordered dictionaries in several modules.
- The `ConfigParser` module uses them by default, meaning that configuration files can now be read, modified, and then written back in their original order.
- The [`_asdict()`](../library/collections.xhtml#collections.somenamedtuple._asdict "collections.somenamedtuple._asdict") method for [`collections.namedtuple()`](../library/collections.xhtml#collections.namedtuple "collections.namedtuple") now returns an ordered dictionary with the values appearing in the same order as the underlying tuple indices.
- The [`json`](../library/json.xhtml#module-json "json: Encode and decode the JSON format.") module's [`JSONDecoder`](../library/json.xhtml#json.JSONDecoder "json.JSONDecoder") class constructor was extended with an *object\_pairs\_hook* parameter to allow `OrderedDict` instances to be built by the decoder. Support was also added for third-party tools like [PyYAML](http://pyyaml.org/) \[http://pyyaml.org/\].
參見
[**PEP 372**](https://www.python.org/dev/peps/pep-0372) \[https://www.python.org/dev/peps/pep-0372\] - Adding an ordered dictionary to collectionsPEP written by Armin Ronacher and Raymond Hettinger; implemented by Raymond Hettinger.
## PEP 378: Format Specifier for Thousands Separator
To make program output more readable, it can be useful to add separators to large numbers, rendering them as 18,446,744,073,709,551,616 instead of 18446744073709551616.
The fully general solution for doing this is the [`locale`](../library/locale.xhtml#module-locale "locale: Internationalization services.") module, which can use different separators ("," in North America, "." in Europe) and different grouping sizes, but [`locale`](../library/locale.xhtml#module-locale "locale: Internationalization services.") is complicated to use and unsuitable for multi-threaded applications where different threads are producing output for different locales.
Therefore, a simple comma-grouping mechanism has been added to the mini-language used by the [`str.format()`](../library/stdtypes.xhtml#str.format "str.format") method. When formatting a floating-point number, simply include a comma between the width and the precision:
```
>>> '{:20,.2f}'.format(18446744073709551616.0)
'18,446,744,073,709,551,616.00'
```
When formatting an integer, include the comma after the width:
```
>>> '{:20,d}'.format(18446744073709551616)
'18,446,744,073,709,551,616'
```
This mechanism is not adaptable at all; commas are always used as the separator and the grouping is always into three-digit groups. The comma-formatting mechanism isn't as general as the [`locale`](../library/locale.xhtml#module-locale "locale: Internationalization services.")module, but it's easier to use.
參見
[**PEP 378**](https://www.python.org/dev/peps/pep-0378) \[https://www.python.org/dev/peps/pep-0378\] - Format Specifier for Thousands SeparatorPEP written by Raymond Hettinger; implemented by Eric Smith.
## PEP 389: The argparse Module for Parsing Command Lines
The [`argparse`](../library/argparse.xhtml#module-argparse "argparse: Command-line option and argument parsing library.") module for parsing command-line arguments was added as a more powerful replacement for the [`optparse`](../library/optparse.xhtml#module-optparse "optparse: Command-line option parsing library. (已移除)") module.
This means Python now supports three different modules for parsing command-line arguments: [`getopt`](../library/getopt.xhtml#module-getopt "getopt: Portable parser for command line options; support both short and long option names."), [`optparse`](../library/optparse.xhtml#module-optparse "optparse: Command-line option parsing library. (已移除)"), and [`argparse`](../library/argparse.xhtml#module-argparse "argparse: Command-line option and argument parsing library."). The [`getopt`](../library/getopt.xhtml#module-getopt "getopt: Portable parser for command line options; support both short and long option names.") module closely resembles the C library's `getopt()` function, so it remains useful if you're writing a Python prototype that will eventually be rewritten in C. [`optparse`](../library/optparse.xhtml#module-optparse "optparse: Command-line option parsing library. (已移除)") becomes redundant, but there are no plans to remove it because there are many scripts still using it, and there's no automated way to update these scripts. (Making the [`argparse`](../library/argparse.xhtml#module-argparse "argparse: Command-line option and argument parsing library.")API consistent with [`optparse`](../library/optparse.xhtml#module-optparse "optparse: Command-line option parsing library. (已移除)")'s interface was discussed but rejected as too messy and difficult.)
In short, if you're writing a new script and don't need to worry about compatibility with earlier versions of Python, use [`argparse`](../library/argparse.xhtml#module-argparse "argparse: Command-line option and argument parsing library.") instead of [`optparse`](../library/optparse.xhtml#module-optparse "optparse: Command-line option parsing library. (已移除)").
Here's an example:
```
import argparse
parser = argparse.ArgumentParser(description='Command-line example.')
# Add optional switches
parser.add_argument('-v', action='store_true', dest='is_verbose',
help='produce verbose output')
parser.add_argument('-o', action='store', dest='output',
metavar='FILE',
help='direct output to FILE instead of stdout')
parser.add_argument('-C', action='store', type=int, dest='context',
metavar='NUM', default=0,
help='display NUM lines of added context')
# Allow any number of additional arguments.
parser.add_argument(nargs='*', action='store', dest='inputs',
help='input filenames (default is stdin)')
args = parser.parse_args()
print args.__dict__
```
Unless you override it, `-h` and `--help` switches are automatically added, and produce neatly formatted output:
```
-> ./python.exe argparse-example.py --help
usage: argparse-example.py [-h] [-v] [-o FILE] [-C NUM] [inputs [inputs ...]]
Command-line example.
positional arguments:
inputs input filenames (default is stdin)
optional arguments:
-h, --help show this help message and exit
-v produce verbose output
-o FILE direct output to FILE instead of stdout
-C NUM display NUM lines of added context
```
As with [`optparse`](../library/optparse.xhtml#module-optparse "optparse: Command-line option parsing library. (已移除)"), the command-line switches and arguments are returned as an object with attributes named by the *dest* parameters:
```
-> ./python.exe argparse-example.py -v
{'output': None,
'is_verbose': True,
'context': 0,
'inputs': []}
-> ./python.exe argparse-example.py -v -o /tmp/output -C 4 file1 file2
{'output': '/tmp/output',
'is_verbose': True,
'context': 4,
'inputs': ['file1', 'file2']}
```
[`argparse`](../library/argparse.xhtml#module-argparse "argparse: Command-line option and argument parsing library.") has much fancier validation than [`optparse`](../library/optparse.xhtml#module-optparse "optparse: Command-line option parsing library. (已移除)"); you can specify an exact number of arguments as an integer, 0 or more arguments by passing `'*'`, 1 or more by passing `'+'`, or an optional argument with `'?'`. A top-level parser can contain sub-parsers to define subcommands that have different sets of switches, as in `svn commit`, `svn checkout`, etc. You can specify an argument's type as [`FileType`](../library/argparse.xhtml#argparse.FileType "argparse.FileType"), which will automatically open files for you and understands that `'-'` means standard input or output.
參見
[`argparse`](../library/argparse.xhtml#module-argparse "argparse: Command-line option and argument parsing library.") documentationThe documentation page of the argparse module.
[Upgrading optparse code](../library/argparse.xhtml#upgrading-optparse-code)Part of the Python documentation, describing how to convert code that uses [`optparse`](../library/optparse.xhtml#module-optparse "optparse: Command-line option parsing library. (已移除)").
[**PEP 389**](https://www.python.org/dev/peps/pep-0389) \[https://www.python.org/dev/peps/pep-0389\] - argparse - New Command Line Parsing ModulePEP written and implemented by Steven Bethard.
## PEP 391: Dictionary-Based Configuration For Logging
The [`logging`](../library/logging.xhtml#module-logging "logging: Flexible event logging system for applications.") module is very flexible; applications can define a tree of logging subsystems, and each logger in this tree can filter out certain messages, format them differently, and direct messages to a varying number of handlers.
All this flexibility can require a lot of configuration. You can write Python statements to create objects and set their properties, but a complex set-up requires verbose but boring code. [`logging`](../library/logging.xhtml#module-logging "logging: Flexible event logging system for applications.") also supports a `fileConfig()`function that parses a file, but the file format doesn't support configuring filters, and it's messier to generate programmatically.
Python 2.7 adds a `dictConfig()` function that uses a dictionary to configure logging. There are many ways to produce a dictionary from different sources: construct one with code; parse a file containing JSON; or use a YAML parsing library if one is installed. For more information see [Configuration functions](../library/logging.config.xhtml#logging-config-api).
The following example configures two loggers, the root logger and a logger named "network". Messages sent to the root logger will be sent to the system log using the syslog protocol, and messages to the "network" logger will be written to a `network.log` file that will be rotated once the log reaches 1MB.
```
import logging
import logging.config
configdict = {
'version': 1, # Configuration schema in use; must be 1 for now
'formatters': {
'standard': {
'format': ('%(asctime)s %(name)-15s '
'%(levelname)-8s %(message)s')}},
'handlers': {'netlog': {'backupCount': 10,
'class': 'logging.handlers.RotatingFileHandler',
'filename': '/logs/network.log',
'formatter': 'standard',
'level': 'INFO',
'maxBytes': 1000000},
'syslog': {'class': 'logging.handlers.SysLogHandler',
'formatter': 'standard',
'level': 'ERROR'}},
# Specify all the subordinate loggers
'loggers': {
'network': {
'handlers': ['netlog']
}
},
# Specify properties of the root logger
'root': {
'handlers': ['syslog']
},
}
# Set up configuration
logging.config.dictConfig(configdict)
# As an example, log two error messages
logger = logging.getLogger('/')
logger.error('Database not found')
netlogger = logging.getLogger('network')
netlogger.error('Connection failed')
```
Three smaller enhancements to the [`logging`](../library/logging.xhtml#module-logging "logging: Flexible event logging system for applications.") module, all implemented by Vinay Sajip, are:
- The [`SysLogHandler`](../library/logging.handlers.xhtml#logging.handlers.SysLogHandler "logging.handlers.SysLogHandler") class now supports syslogging over TCP. The constructor has a *socktype* parameter giving the type of socket to use, either [`socket.SOCK_DGRAM`](../library/socket.xhtml#socket.SOCK_DGRAM "socket.SOCK_DGRAM")for UDP or [`socket.SOCK_STREAM`](../library/socket.xhtml#socket.SOCK_STREAM "socket.SOCK_STREAM") for TCP. The default protocol remains UDP.
- [`Logger`](../library/logging.xhtml#logging.Logger "logging.Logger") instances gained a [`getChild()`](../library/logging.xhtml#logging.Logger.getChild "logging.Logger.getChild")method that retrieves a descendant logger using a relative path. For example, once you retrieve a logger by doing `log = getLogger('app')`, calling `log.getChild('network.listen')` is equivalent to `getLogger('app.network.listen')`.
- The [`LoggerAdapter`](../library/logging.xhtml#logging.LoggerAdapter "logging.LoggerAdapter") class gained an `isEnabledFor()` method that takes a *level* and returns whether the underlying logger would process a message of that level of importance.
參見
[**PEP 391**](https://www.python.org/dev/peps/pep-0391) \[https://www.python.org/dev/peps/pep-0391\] - Dictionary-Based Configuration For LoggingPEP written and implemented by Vinay Sajip.
## PEP 3106: Dictionary Views
The dictionary methods [`keys()`](../library/stdtypes.xhtml#dict.keys "dict.keys"), [`values()`](../library/stdtypes.xhtml#dict.values "dict.values"), and [`items()`](../library/stdtypes.xhtml#dict.items "dict.items") are different in Python 3.x. They return an object called a *view* instead of a fully materialized list.
It's not possible to change the return values of [`keys()`](../library/stdtypes.xhtml#dict.keys "dict.keys"), [`values()`](../library/stdtypes.xhtml#dict.values "dict.values"), and [`items()`](../library/stdtypes.xhtml#dict.items "dict.items") in Python 2.7 because too much code would break. Instead the 3.x versions were added under the new names `viewkeys()`, `viewvalues()`, and `viewitems()`.
```
>>> d = dict((i*10, chr(65+i)) for i in range(26))
>>> d
{0: 'A', 130: 'N', 10: 'B', 140: 'O', 20: ..., 250: 'Z'}
>>> d.viewkeys()
dict_keys([0, 130, 10, 140, 20, 150, 30, ..., 250])
```
Views can be iterated over, but the key and item views also behave like sets. The `&` operator performs intersection, and `|`performs a union:
```
>>> d1 = dict((i*10, chr(65+i)) for i in range(26))
>>> d2 = dict((i**.5, i) for i in range(1000))
>>> d1.viewkeys() & d2.viewkeys()
set([0.0, 10.0, 20.0, 30.0])
>>> d1.viewkeys() | range(0, 30)
set([0, 1, 130, 3, 4, 5, 6, ..., 120, 250])
```
The view keeps track of the dictionary and its contents change as the dictionary is modified:
```
>>> vk = d.viewkeys()
>>> vk
dict_keys([0, 130, 10, ..., 250])
>>> d[260] = '&'
>>> vk
dict_keys([0, 130, 260, 10, ..., 250])
```
However, note that you can't add or remove keys while you're iterating over the view:
```
>>> for k in vk:
... d[k*2] = k
...
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
RuntimeError: dictionary changed size during iteration
```
You can use the view methods in Python 2.x code, and the 2to3 converter will change them to the standard [`keys()`](../library/stdtypes.xhtml#dict.keys "dict.keys"), [`values()`](../library/stdtypes.xhtml#dict.values "dict.values"), and [`items()`](../library/stdtypes.xhtml#dict.items "dict.items") methods.
參見
[**PEP 3106**](https://www.python.org/dev/peps/pep-3106) \[https://www.python.org/dev/peps/pep-3106\] - Revamping dict.keys(), .values() and .items()PEP written by Guido van Rossum. Backported to 2.7 by Alexandre Vassalotti; [bpo-1967](https://bugs.python.org/issue1967) \[https://bugs.python.org/issue1967\].
## PEP 3137: The memoryview Object
The [`memoryview`](../library/stdtypes.xhtml#memoryview "memoryview") object provides a view of another object's memory content that matches the [`bytes`](../library/stdtypes.xhtml#bytes "bytes") type's interface.
```
>>> import string
>>> m = memoryview(string.letters)
>>> m
<memory at 0x37f850>
>>> len(m) # Returns length of underlying object
52
>>> m[0], m[25], m[26] # Indexing returns one byte
('a', 'z', 'A')
>>> m2 = m[0:26] # Slicing returns another memoryview
>>> m2
<memory at 0x37f080>
```
The content of the view can be converted to a string of bytes or a list of integers:
```
>>> m2.tobytes()
'abcdefghijklmnopqrstuvwxyz'
>>> m2.tolist()
[97, 98, 99, 100, 101, 102, 103, ... 121, 122]
>>>
```
[`memoryview`](../library/stdtypes.xhtml#memoryview "memoryview") objects allow modifying the underlying object if it's a mutable object.
```
>>> m2[0] = 75
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: cannot modify read-only memory
>>> b = bytearray(string.letters) # Creating a mutable object
>>> b
bytearray(b'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ')
>>> mb = memoryview(b)
>>> mb[0] = '*' # Assign to view, changing the bytearray.
>>> b[0:5] # The bytearray has been changed.
bytearray(b'*bcde')
>>>
```
參見
[**PEP 3137**](https://www.python.org/dev/peps/pep-3137) \[https://www.python.org/dev/peps/pep-3137\] - Immutable Bytes and Mutable BufferPEP written by Guido van Rossum. Implemented by Travis Oliphant, Antoine Pitrou and others. Backported to 2.7 by Antoine Pitrou; [bpo-2396](https://bugs.python.org/issue2396) \[https://bugs.python.org/issue2396\].
## 其他語言特性修改
Some smaller changes made to the core Python language are:
- The syntax for set literals has been backported from Python 3.x. Curly brackets are used to surround the contents of the resulting mutable set; set literals are distinguished from dictionaries by not containing colons and values. `{}` continues to represent an empty dictionary; use `set()` for an empty set.
```
>>> {1, 2, 3, 4, 5}
set([1, 2, 3, 4, 5])
>>> set() # empty set
set([])
>>> {} # empty dict
{}
```
Backported by Alexandre Vassalotti; [bpo-2335](https://bugs.python.org/issue2335) \[https://bugs.python.org/issue2335\].
- Dictionary and set comprehensions are another feature backported from 3.x, generalizing list/generator comprehensions to use the literal syntax for sets and dictionaries.
```
>>> {x: x*x for x in range(6)}
{0: 0, 1: 1, 2: 4, 3: 9, 4: 16, 5: 25}
>>> {('a'*x) for x in range(6)}
set(['', 'a', 'aa', 'aaa', 'aaaa', 'aaaaa'])
```
Backported by Alexandre Vassalotti; [bpo-2333](https://bugs.python.org/issue2333) \[https://bugs.python.org/issue2333\].
- The [`with`](../reference/compound_stmts.xhtml#with) statement can now use multiple context managers in one statement. Context managers are processed from left to right and each one is treated as beginning a new `with` statement. This means that:
```
with A() as a, B() as b:
... suite of statements ...
```
相當于:
```
with A() as a:
with B() as b:
... suite of statements ...
```
The `contextlib.nested()` function provides a very similar function, so it's no longer necessary and has been deprecated.
(Proposed in <https://codereview.appspot.com/53094>; implemented by Georg Brandl.)
- Conversions between floating-point numbers and strings are now correctly rounded on most platforms. These conversions occur in many different places: [`str()`](../library/stdtypes.xhtml#str "str") on floats and complex numbers; the [`float`](../library/functions.xhtml#float "float") and [`complex`](../library/functions.xhtml#complex "complex")constructors; numeric formatting; serializing and deserializing floats and complex numbers using the [`marshal`](../library/marshal.xhtml#module-marshal "marshal: Convert Python objects to streams of bytes and back (with different constraints)."), [`pickle`](../library/pickle.xhtml#module-pickle "pickle: Convert Python objects to streams of bytes and back.")and [`json`](../library/json.xhtml#module-json "json: Encode and decode the JSON format.") modules; parsing of float and imaginary literals in Python code; and [`Decimal`](../library/decimal.xhtml#decimal.Decimal "decimal.Decimal")-to-float conversion.
Related to this, the [`repr()`](../library/functions.xhtml#repr "repr") of a floating-point number *x*now returns a result based on the shortest decimal string that's guaranteed to round back to *x* under correct rounding (with round-half-to-even rounding mode). Previously it gave a string based on rounding x to 17 decimal digits.
The rounding library responsible for this improvement works on Windows and on Unix platforms using the gcc, icc, or suncc compilers. There may be a small number of platforms where correct operation of this code cannot be guaranteed, so the code is not used on such systems. You can find out which code is being used by checking [`sys.float_repr_style`](../library/sys.xhtml#sys.float_repr_style "sys.float_repr_style"), which will be `short`if the new code is in use and `legacy` if it isn't.
Implemented by Eric Smith and Mark Dickinson, using David Gay's `dtoa.c` library; [bpo-7117](https://bugs.python.org/issue7117) \[https://bugs.python.org/issue7117\].
- Conversions from long integers and regular integers to floating point now round differently, returning the floating-point number closest to the number. This doesn't matter for small integers that can be converted exactly, but for large numbers that will unavoidably lose precision, Python 2.7 now approximates more closely. For example, Python 2.6 computed the following:
```
>>> n = 295147905179352891391
>>> float(n)
2.9514790517935283e+20
>>> n - long(float(n))
65535L
```
Python 2.7's floating-point result is larger, but much closer to the true value:
```
>>> n = 295147905179352891391
>>> float(n)
2.9514790517935289e+20
>>> n - long(float(n))
-1L
```
(Implemented by Mark Dickinson; [bpo-3166](https://bugs.python.org/issue3166) \[https://bugs.python.org/issue3166\].)
Integer division is also more accurate in its rounding behaviours. (Also implemented by Mark Dickinson; [bpo-1811](https://bugs.python.org/issue1811) \[https://bugs.python.org/issue1811\].)
- Implicit coercion for complex numbers has been removed; the interpreter will no longer ever attempt to call a `__coerce__()` method on complex objects. (Removed by Meador Inge and Mark Dickinson; [bpo-5211](https://bugs.python.org/issue5211) \[https://bugs.python.org/issue5211\].)
- The [`str.format()`](../library/stdtypes.xhtml#str.format "str.format") method now supports automatic numbering of the replacement fields. This makes using [`str.format()`](../library/stdtypes.xhtml#str.format "str.format") more closely resemble using `%s` formatting:
```
>>> '{}:{}:{}'.format(2009, 04, 'Sunday')
'2009:4:Sunday'
>>> '{}:{}:{day}'.format(2009, 4, day='Sunday')
'2009:4:Sunday'
```
The auto-numbering takes the fields from left to right, so the first `{...}`specifier will use the first argument to [`str.format()`](../library/stdtypes.xhtml#str.format "str.format"), the next specifier will use the next argument, and so on. You can't mix auto-numbering and explicit numbering -- either number all of your specifier fields or none of them -- but you can mix auto-numbering and named fields, as in the second example above. (Contributed by Eric Smith; [bpo-5237](https://bugs.python.org/issue5237) \[https://bugs.python.org/issue5237\].)
Complex numbers now correctly support usage with [`format()`](../library/functions.xhtml#format "format"), and default to being right-aligned. Specifying a precision or comma-separation applies to both the real and imaginary parts of the number, but a specified field width and alignment is applied to the whole of the resulting `1.5+3j`output. (Contributed by Eric Smith; [bpo-1588](https://bugs.python.org/issue1588) \[https://bugs.python.org/issue1588\] and [bpo-7988](https://bugs.python.org/issue7988) \[https://bugs.python.org/issue7988\].)
The 'F' format code now always formats its output using uppercase characters, so it will now produce 'INF' and 'NAN'. (Contributed by Eric Smith; [bpo-3382](https://bugs.python.org/issue3382) \[https://bugs.python.org/issue3382\].)
A low-level change: the [`object.__format__()`](../reference/datamodel.xhtml#object.__format__ "object.__format__") method now triggers a [`PendingDeprecationWarning`](../library/exceptions.xhtml#PendingDeprecationWarning "PendingDeprecationWarning") if it's passed a format string, because the [`__format__()`](../reference/datamodel.xhtml#object.__format__ "object.__format__") method for [`object`](../library/functions.xhtml#object "object") converts the object to a string representation and formats that. Previously the method silently applied the format string to the string representation, but that could hide mistakes in Python code. If you're supplying formatting information such as an alignment or precision, presumably you're expecting the formatting to be applied in some object-specific way. (Fixed by Eric Smith; [bpo-7994](https://bugs.python.org/issue7994) \[https://bugs.python.org/issue7994\].)
- The [`int()`](../library/functions.xhtml#int "int") and `long()` types gained a `bit_length`method that returns the number of bits necessary to represent its argument in binary:
```
>>> n = 37
>>> bin(n)
'0b100101'
>>> n.bit_length()
6
>>> n = 2**123-1
>>> n.bit_length()
123
>>> (n+1).bit_length()
124
```
(Contributed by Fredrik Johansson and Victor Stinner; [bpo-3439](https://bugs.python.org/issue3439) \[https://bugs.python.org/issue3439\].)
- The [`import`](../reference/simple_stmts.xhtml#import) statement will no longer try an absolute import if a relative import (e.g. `from .os import sep`) fails. This fixes a bug, but could possibly break certain `import`statements that were only working by accident. (Fixed by Meador Inge; [bpo-7902](https://bugs.python.org/issue7902) \[https://bugs.python.org/issue7902\].)
- It's now possible for a subclass of the built-in `unicode` type to override the `__unicode__()` method. (Implemented by Victor Stinner; [bpo-1583863](https://bugs.python.org/issue1583863) \[https://bugs.python.org/issue1583863\].)
- The [`bytearray`](../library/stdtypes.xhtml#bytearray "bytearray") type's [`translate()`](../library/stdtypes.xhtml#bytearray.translate "bytearray.translate") method now accepts `None` as its first argument. (Fixed by Georg Brandl; [bpo-4759](https://bugs.python.org/issue4759) \[https://bugs.python.org/issue4759\].)
- When using `@classmethod` and `@staticmethod` to wrap methods as class or static methods, the wrapper object now exposes the wrapped function as their `__func__` attribute. (Contributed by Amaury Forgeot d'Arc, after a suggestion by George Sakkis; [bpo-5982](https://bugs.python.org/issue5982) \[https://bugs.python.org/issue5982\].)
- When a restricted set of attributes were set using `__slots__`, deleting an unset attribute would not raise [`AttributeError`](../library/exceptions.xhtml#AttributeError "AttributeError")as you would expect. Fixed by Benjamin Peterson; [bpo-7604](https://bugs.python.org/issue7604) \[https://bugs.python.org/issue7604\].)
- Two new encodings are now supported: "cp720", used primarily for Arabic text; and "cp858", a variant of CP 850 that adds the euro symbol. (CP720 contributed by Alexander Belchenko and Amaury Forgeot d'Arc in [bpo-1616979](https://bugs.python.org/issue1616979) \[https://bugs.python.org/issue1616979\]; CP858 contributed by Tim Hatch in [bpo-8016](https://bugs.python.org/issue8016) \[https://bugs.python.org/issue8016\].)
- The `file` object will now set the `filename` attribute on the [`IOError`](../library/exceptions.xhtml#IOError "IOError") exception when trying to open a directory on POSIX platforms (noted by Jan Kaliszewski; [bpo-4764](https://bugs.python.org/issue4764) \[https://bugs.python.org/issue4764\]), and now explicitly checks for and forbids writing to read-only file objects instead of trusting the C library to catch and report the error (fixed by Stefan Krah; [bpo-5677](https://bugs.python.org/issue5677) \[https://bugs.python.org/issue5677\]).
- The Python tokenizer now translates line endings itself, so the [`compile()`](../library/functions.xhtml#compile "compile") built-in function now accepts code using any line-ending convention. Additionally, it no longer requires that the code end in a newline.
- Extra parentheses in function definitions are illegal in Python 3.x, meaning that you get a syntax error from `def f((x)): pass`. In Python3-warning mode, Python 2.7 will now warn about this odd usage. (Noted by James Lingard; [bpo-7362](https://bugs.python.org/issue7362) \[https://bugs.python.org/issue7362\].)
- It's now possible to create weak references to old-style class objects. New-style classes were always weak-referenceable. (Fixed by Antoine Pitrou; [bpo-8268](https://bugs.python.org/issue8268) \[https://bugs.python.org/issue8268\].)
- When a module object is garbage-collected, the module's dictionary is now only cleared if no one else is holding a reference to the dictionary ([bpo-7140](https://bugs.python.org/issue7140) \[https://bugs.python.org/issue7140\]).
### Interpreter Changes
A new environment variable, [`PYTHONWARNINGS`](../using/cmdline.xhtml#envvar-PYTHONWARNINGS), allows controlling warnings. It should be set to a string containing warning settings, equivalent to those used with the [`-W`](../using/cmdline.xhtml#cmdoption-w) switch, separated by commas. (Contributed by Brian Curtin; [bpo-7301](https://bugs.python.org/issue7301) \[https://bugs.python.org/issue7301\].)
For example, the following setting will print warnings every time they occur, but turn warnings from the `Cookie` module into an error. (The exact syntax for setting an environment variable varies across operating systems and shells.)
```
export PYTHONWARNINGS=all,error:::Cookie:0
```
### 性能優化
Several performance enhancements have been added:
- A new opcode was added to perform the initial setup for [`with`](../reference/compound_stmts.xhtml#with) statements, looking up the [`__enter__()`](../reference/datamodel.xhtml#object.__enter__ "object.__enter__") and [`__exit__()`](../reference/datamodel.xhtml#object.__exit__ "object.__exit__") methods. (Contributed by Benjamin Peterson.)
- The garbage collector now performs better for one common usage pattern: when many objects are being allocated without deallocating any of them. This would previously take quadratic time for garbage collection, but now the number of full garbage collections is reduced as the number of objects on the heap grows. The new logic only performs a full garbage collection pass when the middle generation has been collected 10 times and when the number of survivor objects from the middle generation exceeds 10% of the number of objects in the oldest generation. (Suggested by Martin von L?wis and implemented by Antoine Pitrou; [bpo-4074](https://bugs.python.org/issue4074) \[https://bugs.python.org/issue4074\].)
- The garbage collector tries to avoid tracking simple containers which can't be part of a cycle. In Python 2.7, this is now true for tuples and dicts containing atomic types (such as ints, strings, etc.). Transitively, a dict containing tuples of atomic types won't be tracked either. This helps reduce the cost of each garbage collection by decreasing the number of objects to be considered and traversed by the collector. (Contributed by Antoine Pitrou; [bpo-4688](https://bugs.python.org/issue4688) \[https://bugs.python.org/issue4688\].)
- Long integers are now stored internally either in base 2\*\*15 or in base 2\*\*30, the base being determined at build time. Previously, they were always stored in base 2\*\*15. Using base 2\*\*30 gives significant performance improvements on 64-bit machines, but benchmark results on 32-bit machines have been mixed. Therefore, the default is to use base 2\*\*30 on 64-bit machines and base 2\*\*15 on 32-bit machines; on Unix, there's a new configure option `--enable-big-digits` that can be used to override this default.
Apart from the performance improvements this change should be invisible to end users, with one exception: for testing and debugging purposes there's a new structseq `sys.long_info` that provides information about the internal format, giving the number of bits per digit and the size in bytes of the C type used to store each digit:
```
>>> import sys
>>> sys.long_info
sys.long_info(bits_per_digit=30, sizeof_digit=4)
```
(Contributed by Mark Dickinson; [bpo-4258](https://bugs.python.org/issue4258) \[https://bugs.python.org/issue4258\].)
Another set of changes made long objects a few bytes smaller: 2 bytes smaller on 32-bit systems and 6 bytes on 64-bit. (Contributed by Mark Dickinson; [bpo-5260](https://bugs.python.org/issue5260) \[https://bugs.python.org/issue5260\].)
- The division algorithm for long integers has been made faster by tightening the inner loop, doing shifts instead of multiplications, and fixing an unnecessary extra iteration. Various benchmarks show speedups of between 50% and 150% for long integer divisions and modulo operations. (Contributed by Mark Dickinson; [bpo-5512](https://bugs.python.org/issue5512) \[https://bugs.python.org/issue5512\].) Bitwise operations are also significantly faster (initial patch by Gregory Smith; [bpo-1087418](https://bugs.python.org/issue1087418) \[https://bugs.python.org/issue1087418\]).
- The implementation of `%` checks for the left-side operand being a Python string and special-cases it; this results in a 1--3% performance increase for applications that frequently use `%`with strings, such as templating libraries. (Implemented by Collin Winter; [bpo-5176](https://bugs.python.org/issue5176) \[https://bugs.python.org/issue5176\].)
- List comprehensions with an `if` condition are compiled into faster bytecode. (Patch by Antoine Pitrou, back-ported to 2.7 by Jeffrey Yasskin; [bpo-4715](https://bugs.python.org/issue4715) \[https://bugs.python.org/issue4715\].)
- Converting an integer or long integer to a decimal string was made faster by special-casing base 10 instead of using a generalized conversion function that supports arbitrary bases. (Patch by Gawain Bolton; [bpo-6713](https://bugs.python.org/issue6713) \[https://bugs.python.org/issue6713\].)
- The `split()`, `replace()`, `rindex()`, `rpartition()`, and `rsplit()` methods of string-like types (strings, Unicode strings, and [`bytearray`](../library/stdtypes.xhtml#bytearray "bytearray") objects) now use a fast reverse-search algorithm instead of a character-by-character scan. This is sometimes faster by a factor of 10. (Added by Florent Xicluna; [bpo-7462](https://bugs.python.org/issue7462) \[https://bugs.python.org/issue7462\] and [bpo-7622](https://bugs.python.org/issue7622) \[https://bugs.python.org/issue7622\].)
- The [`pickle`](../library/pickle.xhtml#module-pickle "pickle: Convert Python objects to streams of bytes and back.") and `cPickle` modules now automatically intern the strings used for attribute names, reducing memory usage of the objects resulting from unpickling. (Contributed by Jake McGuire; [bpo-5084](https://bugs.python.org/issue5084) \[https://bugs.python.org/issue5084\].)
- The `cPickle` module now special-cases dictionaries, nearly halving the time required to pickle them. (Contributed by Collin Winter; [bpo-5670](https://bugs.python.org/issue5670) \[https://bugs.python.org/issue5670\].)
## New and Improved Modules
As in every release, Python's standard library received a number of enhancements and bug fixes. Here's a partial list of the most notable changes, sorted alphabetically by module name. Consult the `Misc/NEWS` file in the source tree for a more complete list of changes, or look through the Subversion logs for all the details.
- The [`bdb`](../library/bdb.xhtml#module-bdb "bdb: Debugger framework.") module's base debugging class [`Bdb`](../library/bdb.xhtml#bdb.Bdb "bdb.Bdb")gained a feature for skipping modules. The constructor now takes an iterable containing glob-style patterns such as `django.*`; the debugger will not step into stack frames from a module that matches one of these patterns. (Contributed by Maru Newby after a suggestion by Senthil Kumaran; [bpo-5142](https://bugs.python.org/issue5142) \[https://bugs.python.org/issue5142\].)
- The [`binascii`](../library/binascii.xhtml#module-binascii "binascii: Tools for converting between binary and various ASCII-encoded binary representations.") module now supports the buffer API, so it can be used with [`memoryview`](../library/stdtypes.xhtml#memoryview "memoryview") instances and other similar buffer objects. (Backported from 3.x by Florent Xicluna; [bpo-7703](https://bugs.python.org/issue7703) \[https://bugs.python.org/issue7703\].)
- Updated module: the `bsddb` module has been updated from 4.7.2devel9 to version 4.8.4 of [the pybsddb package](https://www.jcea.es/programacion/pybsddb.htm) \[https://www.jcea.es/programacion/pybsddb.htm\]. The new version features better Python 3.x compatibility, various bug fixes, and adds several new BerkeleyDB flags and methods. (Updated by Jesús Cea Avión; [bpo-8156](https://bugs.python.org/issue8156) \[https://bugs.python.org/issue8156\]. The pybsddb changelog can be read at <http://hg.jcea.es/pybsddb/file/tip/ChangeLog>.)
- The [`bz2`](../library/bz2.xhtml#module-bz2 "bz2: Interfaces for bzip2 compression and decompression.") module's [`BZ2File`](../library/bz2.xhtml#bz2.BZ2File "bz2.BZ2File") now supports the context management protocol, so you can write `with bz2.BZ2File(...) as f:`. (Contributed by Hagen Fürstenau; [bpo-3860](https://bugs.python.org/issue3860) \[https://bugs.python.org/issue3860\].)
- New class: the [`Counter`](../library/collections.xhtml#collections.Counter "collections.Counter") class in the [`collections`](../library/collections.xhtml#module-collections "collections: Container datatypes")module is useful for tallying data. [`Counter`](../library/collections.xhtml#collections.Counter "collections.Counter") instances behave mostly like dictionaries but return zero for missing keys instead of raising a [`KeyError`](../library/exceptions.xhtml#KeyError "KeyError"):
```
>>> from collections import Counter
>>> c = Counter()
>>> for letter in 'here is a sample of english text':
... c[letter] += 1
...
>>> c
Counter({' ': 6, 'e': 5, 's': 3, 'a': 2, 'i': 2, 'h': 2,
'l': 2, 't': 2, 'g': 1, 'f': 1, 'm': 1, 'o': 1, 'n': 1,
'p': 1, 'r': 1, 'x': 1})
>>> c['e']
5
>>> c['z']
0
```
There are three additional [`Counter`](../library/collections.xhtml#collections.Counter "collections.Counter") methods. [`most_common()`](../library/collections.xhtml#collections.Counter.most_common "collections.Counter.most_common") returns the N most common elements and their counts. [`elements()`](../library/collections.xhtml#collections.Counter.elements "collections.Counter.elements")returns an iterator over the contained elements, repeating each element as many times as its count. [`subtract()`](../library/collections.xhtml#collections.Counter.subtract "collections.Counter.subtract") takes an iterable and subtracts one for each element instead of adding; if the argument is a dictionary or another `Counter`, the counts are subtracted.
```
>>> c.most_common(5)
[(' ', 6), ('e', 5), ('s', 3), ('a', 2), ('i', 2)]
>>> c.elements() ->
'a', 'a', ' ', ' ', ' ', ' ', ' ', ' ',
'e', 'e', 'e', 'e', 'e', 'g', 'f', 'i', 'i',
'h', 'h', 'm', 'l', 'l', 'o', 'n', 'p', 's',
's', 's', 'r', 't', 't', 'x'
>>> c['e']
5
>>> c.subtract('very heavy on the letter e')
>>> c['e'] # Count is now lower
-1
```
Contributed by Raymond Hettinger; [bpo-1696199](https://bugs.python.org/issue1696199) \[https://bugs.python.org/issue1696199\].
New class: [`OrderedDict`](../library/collections.xhtml#collections.OrderedDict "collections.OrderedDict") is described in the earlier section [PEP 372: Adding an Ordered Dictionary to collections](#pep-0372).
New method: The [`deque`](../library/collections.xhtml#collections.deque "collections.deque") data type now has a [`count()`](../library/collections.xhtml#collections.deque.count "collections.deque.count") method that returns the number of contained elements equal to the supplied argument *x*, and a [`reverse()`](../library/collections.xhtml#collections.deque.reverse "collections.deque.reverse") method that reverses the elements of the deque in-place. [`deque`](../library/collections.xhtml#collections.deque "collections.deque") also exposes its maximum length as the read-only [`maxlen`](../library/collections.xhtml#collections.deque.maxlen "collections.deque.maxlen") attribute. (Both features added by Raymond Hettinger.)
The [`namedtuple`](../library/collections.xhtml#collections.namedtuple "collections.namedtuple") class now has an optional *rename* parameter. If *rename* is true, field names that are invalid because they've been repeated or aren't legal Python identifiers will be renamed to legal names that are derived from the field's position within the list of fields:
```
>>> from collections import namedtuple
>>> T = namedtuple('T', ['field1', '$illegal', 'for', 'field2'], rename=True)
>>> T._fields
('field1', '_1', '_2', 'field2')
```
(Added by Raymond Hettinger; [bpo-1818](https://bugs.python.org/issue1818) \[https://bugs.python.org/issue1818\].)
Finally, the `Mapping` abstract base class now returns [`NotImplemented`](../library/constants.xhtml#NotImplemented "NotImplemented") if a mapping is compared to another type that isn't a `Mapping`. (Fixed by Daniel Stutzbach; [bpo-8729](https://bugs.python.org/issue8729) \[https://bugs.python.org/issue8729\].)
- Constructors for the parsing classes in the `ConfigParser` module now take an *allow\_no\_value* parameter, defaulting to false; if true, options without values will be allowed. For example:
```
>>> import ConfigParser, StringIO
>>> sample_config = """
... [mysqld]
... user = mysql
... pid-file = /var/run/mysqld/mysqld.pid
... skip-bdb
... """
>>> config = ConfigParser.RawConfigParser(allow_no_value=True)
>>> config.readfp(StringIO.StringIO(sample_config))
>>> config.get('mysqld', 'user')
'mysql'
>>> print config.get('mysqld', 'skip-bdb')
None
>>> print config.get('mysqld', 'unknown')
Traceback (most recent call last):
...
NoOptionError: No option 'unknown' in section: 'mysqld'
```
(Contributed by Mats Kindahl; [bpo-7005](https://bugs.python.org/issue7005) \[https://bugs.python.org/issue7005\].)
- Deprecated function: `contextlib.nested()`, which allows handling more than one context manager with a single [`with`](../reference/compound_stmts.xhtml#with)statement, has been deprecated, because the `with` statement now supports multiple context managers.
- The `cookielib` module now ignores cookies that have an invalid version field, one that doesn't contain an integer value. (Fixed by John J. Lee; [bpo-3924](https://bugs.python.org/issue3924) \[https://bugs.python.org/issue3924\].)
- The [`copy`](../library/copy.xhtml#module-copy "copy: Shallow and deep copy operations.") module's [`deepcopy()`](../library/copy.xhtml#copy.deepcopy "copy.deepcopy") function will now correctly copy bound instance methods. (Implemented by Robert Collins; [bpo-1515](https://bugs.python.org/issue1515) \[https://bugs.python.org/issue1515\].)
- The [`ctypes`](../library/ctypes.xhtml#module-ctypes "ctypes: A foreign function library for Python.") module now always converts `None` to a C NULL pointer for arguments declared as pointers. (Changed by Thomas Heller; [bpo-4606](https://bugs.python.org/issue4606) \[https://bugs.python.org/issue4606\].) The underlying [libffi library](https://sourceware.org/libffi/) \[https://sourceware.org/libffi/\] has been updated to version 3.0.9, containing various fixes for different platforms. (Updated by Matthias Klose; [bpo-8142](https://bugs.python.org/issue8142) \[https://bugs.python.org/issue8142\].)
- New method: the [`datetime`](../library/datetime.xhtml#module-datetime "datetime: Basic date and time types.") module's [`timedelta`](../library/datetime.xhtml#datetime.timedelta "datetime.timedelta") class gained a [`total_seconds()`](../library/datetime.xhtml#datetime.timedelta.total_seconds "datetime.timedelta.total_seconds") method that returns the number of seconds in the duration. (Contributed by Brian Quinlan; [bpo-5788](https://bugs.python.org/issue5788) \[https://bugs.python.org/issue5788\].)
- New method: the [`Decimal`](../library/decimal.xhtml#decimal.Decimal "decimal.Decimal") class gained a [`from_float()`](../library/decimal.xhtml#decimal.Decimal.from_float "decimal.Decimal.from_float") class method that performs an exact conversion of a floating-point number to a [`Decimal`](../library/decimal.xhtml#decimal.Decimal "decimal.Decimal"). This exact conversion strives for the closest decimal approximation to the floating-point representation's value; the resulting decimal value will therefore still include the inaccuracy, if any. For example, `Decimal.from_float(0.1)` returns `Decimal('0.1000000000000000055511151231257827021181583404541015625')`. (Implemented by Raymond Hettinger; [bpo-4796](https://bugs.python.org/issue4796) \[https://bugs.python.org/issue4796\].)
Comparing instances of [`Decimal`](../library/decimal.xhtml#decimal.Decimal "decimal.Decimal") with floating-point numbers now produces sensible results based on the numeric values of the operands. Previously such comparisons would fall back to Python's default rules for comparing objects, which produced arbitrary results based on their type. Note that you still cannot combine `Decimal` and floating-point in other operations such as addition, since you should be explicitly choosing how to convert between float and [`Decimal`](../library/decimal.xhtml#decimal.Decimal "decimal.Decimal"). (Fixed by Mark Dickinson; [bpo-2531](https://bugs.python.org/issue2531) \[https://bugs.python.org/issue2531\].)
The constructor for [`Decimal`](../library/decimal.xhtml#decimal.Decimal "decimal.Decimal") now accepts floating-point numbers (added by Raymond Hettinger; [bpo-8257](https://bugs.python.org/issue8257) \[https://bugs.python.org/issue8257\]) and non-European Unicode characters such as Arabic-Indic digits (contributed by Mark Dickinson; [bpo-6595](https://bugs.python.org/issue6595) \[https://bugs.python.org/issue6595\]).
Most of the methods of the [`Context`](../library/decimal.xhtml#decimal.Context "decimal.Context") class now accept integers as well as [`Decimal`](../library/decimal.xhtml#decimal.Decimal "decimal.Decimal") instances; the only exceptions are the [`canonical()`](../library/decimal.xhtml#decimal.Context.canonical "decimal.Context.canonical") and [`is_canonical()`](../library/decimal.xhtml#decimal.Context.is_canonical "decimal.Context.is_canonical")methods. (Patch by Juan José Conti; [bpo-7633](https://bugs.python.org/issue7633) \[https://bugs.python.org/issue7633\].)
When using [`Decimal`](../library/decimal.xhtml#decimal.Decimal "decimal.Decimal") instances with a string's [`format()`](../library/stdtypes.xhtml#str.format "str.format") method, the default alignment was previously left-alignment. This has been changed to right-alignment, which is more sensible for numeric types. (Changed by Mark Dickinson; [bpo-6857](https://bugs.python.org/issue6857) \[https://bugs.python.org/issue6857\].)
Comparisons involving a signaling NaN value (or `sNAN`) now signal `InvalidOperation` instead of silently returning a true or false value depending on the comparison operator. Quiet NaN values (or `NaN`) are now hashable. (Fixed by Mark Dickinson; [bpo-7279](https://bugs.python.org/issue7279) \[https://bugs.python.org/issue7279\].)
- The [`difflib`](../library/difflib.xhtml#module-difflib "difflib: Helpers for computing differences between objects.") module now produces output that is more compatible with modern **diff**/**patch** tools through one small change, using a tab character instead of spaces as a separator in the header giving the filename. (Fixed by Anatoly Techtonik; [bpo-7585](https://bugs.python.org/issue7585) \[https://bugs.python.org/issue7585\].)
- The Distutils `sdist` command now always regenerates the `MANIFEST` file, since even if the `MANIFEST.in` or `setup.py` files haven't been modified, the user might have created some new files that should be included. (Fixed by Tarek Ziadé; [bpo-8688](https://bugs.python.org/issue8688) \[https://bugs.python.org/issue8688\].)
- The [`doctest`](../library/doctest.xhtml#module-doctest "doctest: Test pieces of code within docstrings.") module's `IGNORE_EXCEPTION_DETAIL` flag will now ignore the name of the module containing the exception being tested. (Patch by Lennart Regebro; [bpo-7490](https://bugs.python.org/issue7490) \[https://bugs.python.org/issue7490\].)
- The [`email`](../library/email.xhtml#module-email "email: Package supporting the parsing, manipulating, and generating email messages.") module's [`Message`](../library/email.compat32-message.xhtml#email.message.Message "email.message.Message") class will now accept a Unicode-valued payload, automatically converting the payload to the encoding specified by `output_charset`. (Added by R. David Murray; [bpo-1368247](https://bugs.python.org/issue1368247) \[https://bugs.python.org/issue1368247\].)
- The [`Fraction`](../library/fractions.xhtml#fractions.Fraction "fractions.Fraction") class now accepts a single float or [`Decimal`](../library/decimal.xhtml#decimal.Decimal "decimal.Decimal") instance, or two rational numbers, as arguments to its constructor. (Implemented by Mark Dickinson; rationals added in [bpo-5812](https://bugs.python.org/issue5812) \[https://bugs.python.org/issue5812\], and float/decimal in [bpo-8294](https://bugs.python.org/issue8294) \[https://bugs.python.org/issue8294\].)
Ordering comparisons (`<`, `<=`, `>`, `>=`) between fractions and complex numbers now raise a [`TypeError`](../library/exceptions.xhtml#TypeError "TypeError"). This fixes an oversight, making the [`Fraction`](../library/fractions.xhtml#fractions.Fraction "fractions.Fraction")match the other numeric types.
- New class: [`FTP_TLS`](../library/ftplib.xhtml#ftplib.FTP_TLS "ftplib.FTP_TLS") in the [`ftplib`](../library/ftplib.xhtml#module-ftplib "ftplib: FTP protocol client (requires sockets).") module provides secure FTP connections using TLS encapsulation of authentication as well as subsequent control and data transfers. (Contributed by Giampaolo Rodola; [bpo-2054](https://bugs.python.org/issue2054) \[https://bugs.python.org/issue2054\].)
The [`storbinary()`](../library/ftplib.xhtml#ftplib.FTP.storbinary "ftplib.FTP.storbinary") method for binary uploads can now restart uploads thanks to an added *rest* parameter (patch by Pablo Mouzo; [bpo-6845](https://bugs.python.org/issue6845) \[https://bugs.python.org/issue6845\].)
- New class decorator: [`total_ordering()`](../library/functools.xhtml#functools.total_ordering "functools.total_ordering") in the [`functools`](../library/functools.xhtml#module-functools "functools: Higher-order functions and operations on callable objects.")module takes a class that defines an [`__eq__()`](../reference/datamodel.xhtml#object.__eq__ "object.__eq__") method and one of [`__lt__()`](../reference/datamodel.xhtml#object.__lt__ "object.__lt__"), [`__le__()`](../reference/datamodel.xhtml#object.__le__ "object.__le__"), [`__gt__()`](../reference/datamodel.xhtml#object.__gt__ "object.__gt__"), or [`__ge__()`](../reference/datamodel.xhtml#object.__ge__ "object.__ge__"), and generates the missing comparison methods. Since the `__cmp__()` method is being deprecated in Python 3.x, this decorator makes it easier to define ordered classes. (Added by Raymond Hettinger; [bpo-5479](https://bugs.python.org/issue5479) \[https://bugs.python.org/issue5479\].)
New function: [`cmp_to_key()`](../library/functools.xhtml#functools.cmp_to_key "functools.cmp_to_key") will take an old-style comparison function that expects two arguments and return a new callable that can be used as the *key* parameter to functions such as [`sorted()`](../library/functions.xhtml#sorted "sorted"), [`min()`](../library/functions.xhtml#min "min") and [`max()`](../library/functions.xhtml#max "max"), etc. The primary intended use is to help with making code compatible with Python 3.x. (Added by Raymond Hettinger.)
- New function: the [`gc`](../library/gc.xhtml#module-gc "gc: Interface to the cycle-detecting garbage collector.") module's [`is_tracked()`](../library/gc.xhtml#gc.is_tracked "gc.is_tracked") returns true if a given instance is tracked by the garbage collector, false otherwise. (Contributed by Antoine Pitrou; [bpo-4688](https://bugs.python.org/issue4688) \[https://bugs.python.org/issue4688\].)
- The [`gzip`](../library/gzip.xhtml#module-gzip "gzip: Interfaces for gzip compression and decompression using file objects.") module's [`GzipFile`](../library/gzip.xhtml#gzip.GzipFile "gzip.GzipFile") now supports the context management protocol, so you can write `with gzip.GzipFile(...) as f:`(contributed by Hagen Fürstenau; [bpo-3860](https://bugs.python.org/issue3860) \[https://bugs.python.org/issue3860\]), and it now implements the [`io.BufferedIOBase`](../library/io.xhtml#io.BufferedIOBase "io.BufferedIOBase") ABC, so you can wrap it with [`io.BufferedReader`](../library/io.xhtml#io.BufferedReader "io.BufferedReader") for faster processing (contributed by Nir Aides; [bpo-7471](https://bugs.python.org/issue7471) \[https://bugs.python.org/issue7471\]). It's also now possible to override the modification time recorded in a gzipped file by providing an optional timestamp to the constructor. (Contributed by Jacques Frechet; [bpo-4272](https://bugs.python.org/issue4272) \[https://bugs.python.org/issue4272\].)
Files in gzip format can be padded with trailing zero bytes; the [`gzip`](../library/gzip.xhtml#module-gzip "gzip: Interfaces for gzip compression and decompression using file objects.") module will now consume these trailing bytes. (Fixed by Tadek Pietraszek and Brian Curtin; [bpo-2846](https://bugs.python.org/issue2846) \[https://bugs.python.org/issue2846\].)
- New attribute: the [`hashlib`](../library/hashlib.xhtml#module-hashlib "hashlib: Secure hash and message digest algorithms.") module now has an `algorithms`attribute containing a tuple naming the supported algorithms. In Python 2.7, `hashlib.algorithms` contains `('md5', 'sha1', 'sha224', 'sha256', 'sha384', 'sha512')`. (Contributed by Carl Chenet; [bpo-7418](https://bugs.python.org/issue7418) \[https://bugs.python.org/issue7418\].)
- The default `HTTPResponse` class used by the `httplib` module now supports buffering, resulting in much faster reading of HTTP responses. (Contributed by Kristján Valur Jónsson; [bpo-4879](https://bugs.python.org/issue4879) \[https://bugs.python.org/issue4879\].)
The `HTTPConnection` and `HTTPSConnection` classes now support a *source\_address* parameter, a `(host, port)` 2-tuple giving the source address that will be used for the connection. (Contributed by Eldon Ziegler; [bpo-3972](https://bugs.python.org/issue3972) \[https://bugs.python.org/issue3972\].)
- The `ihooks` module now supports relative imports. Note that `ihooks` is an older module for customizing imports, superseded by the `imputil` module added in Python 2.0. (Relative import support added by Neil Schemenauer.)
- The [`imaplib`](../library/imaplib.xhtml#module-imaplib "imaplib: IMAP4 protocol client (requires sockets).") module now supports IPv6 addresses. (Contributed by Derek Morr; [bpo-1655](https://bugs.python.org/issue1655) \[https://bugs.python.org/issue1655\].)
- New function: the [`inspect`](../library/inspect.xhtml#module-inspect "inspect: Extract information and source code from live objects.") module's [`getcallargs()`](../library/inspect.xhtml#inspect.getcallargs "inspect.getcallargs")takes a callable and its positional and keyword arguments, and figures out which of the callable's parameters will receive each argument, returning a dictionary mapping argument names to their values. For example:
```
>>> from inspect import getcallargs
>>> def f(a, b=1, *pos, **named):
... pass
>>> getcallargs(f, 1, 2, 3)
{'a': 1, 'b': 2, 'pos': (3,), 'named': {}}
>>> getcallargs(f, a=2, x=4)
{'a': 2, 'b': 1, 'pos': (), 'named': {'x': 4}}
>>> getcallargs(f)
Traceback (most recent call last):
...
TypeError: f() takes at least 1 argument (0 given)
```
Contributed by George Sakkis; [bpo-3135](https://bugs.python.org/issue3135) \[https://bugs.python.org/issue3135\].
- Updated module: The [`io`](../library/io.xhtml#module-io "io: Core tools for working with streams.") library has been upgraded to the version shipped with Python 3.1. For 3.1, the I/O library was entirely rewritten in C and is 2 to 20 times faster depending on the task being performed. The original Python version was renamed to the `_pyio` module.
One minor resulting change: the [`io.TextIOBase`](../library/io.xhtml#io.TextIOBase "io.TextIOBase") class now has an `errors` attribute giving the error setting used for encoding and decoding errors (one of `'strict'`, `'replace'`, `'ignore'`).
The [`io.FileIO`](../library/io.xhtml#io.FileIO "io.FileIO") class now raises an [`OSError`](../library/exceptions.xhtml#OSError "OSError") when passed an invalid file descriptor. (Implemented by Benjamin Peterson; [bpo-4991](https://bugs.python.org/issue4991) \[https://bugs.python.org/issue4991\].) The [`truncate()`](../library/io.xhtml#io.IOBase.truncate "io.IOBase.truncate") method now preserves the file position; previously it would change the file position to the end of the new file. (Fixed by Pascal Chambon; [bpo-6939](https://bugs.python.org/issue6939) \[https://bugs.python.org/issue6939\].)
- New function: `itertools.compress(data, selectors)` takes two iterators. Elements of *data* are returned if the corresponding value in *selectors* is true:
```
itertools.compress('ABCDEF', [1,0,1,0,1,1]) =>
A, C, E, F
```
New function: `itertools.combinations_with_replacement(iter, r)`returns all the possible *r*-length combinations of elements from the iterable *iter*. Unlike [`combinations()`](../library/itertools.xhtml#itertools.combinations "itertools.combinations"), individual elements can be repeated in the generated combinations:
```
itertools.combinations_with_replacement('abc', 2) =>
('a', 'a'), ('a', 'b'), ('a', 'c'),
('b', 'b'), ('b', 'c'), ('c', 'c')
```
Note that elements are treated as unique depending on their position in the input, not their actual values.
The [`itertools.count()`](../library/itertools.xhtml#itertools.count "itertools.count") function now has a *step* argument that allows incrementing by values other than 1. [`count()`](../library/itertools.xhtml#itertools.count "itertools.count") also now allows keyword arguments, and using non-integer values such as floats or [`Decimal`](../library/decimal.xhtml#decimal.Decimal "decimal.Decimal") instances. (Implemented by Raymond Hettinger; [bpo-5032](https://bugs.python.org/issue5032) \[https://bugs.python.org/issue5032\].)
[`itertools.combinations()`](../library/itertools.xhtml#itertools.combinations "itertools.combinations") and [`itertools.product()`](../library/itertools.xhtml#itertools.product "itertools.product")previously raised [`ValueError`](../library/exceptions.xhtml#ValueError "ValueError") for values of *r* larger than the input iterable. This was deemed a specification error, so they now return an empty iterator. (Fixed by Raymond Hettinger; [bpo-4816](https://bugs.python.org/issue4816) \[https://bugs.python.org/issue4816\].)
- Updated module: The [`json`](../library/json.xhtml#module-json "json: Encode and decode the JSON format.") module was upgraded to version 2.0.9 of the simplejson package, which includes a C extension that makes encoding and decoding faster. (Contributed by Bob Ippolito; [bpo-4136](https://bugs.python.org/issue4136) \[https://bugs.python.org/issue4136\].)
To support the new [`collections.OrderedDict`](../library/collections.xhtml#collections.OrderedDict "collections.OrderedDict") type, [`json.load()`](../library/json.xhtml#json.load "json.load")now has an optional *object\_pairs\_hook* parameter that will be called with any object literal that decodes to a list of pairs. (Contributed by Raymond Hettinger; [bpo-5381](https://bugs.python.org/issue5381) \[https://bugs.python.org/issue5381\].)
- The [`mailbox`](../library/mailbox.xhtml#module-mailbox "mailbox: Manipulate mailboxes in various formats") module's [`Maildir`](../library/mailbox.xhtml#mailbox.Maildir "mailbox.Maildir") class now records the timestamp on the directories it reads, and only re-reads them if the modification time has subsequently changed. This improves performance by avoiding unneeded directory scans. (Fixed by A.M. Kuchling and Antoine Pitrou; [bpo-1607951](https://bugs.python.org/issue1607951) \[https://bugs.python.org/issue1607951\], [bpo-6896](https://bugs.python.org/issue6896) \[https://bugs.python.org/issue6896\].)
- New functions: the [`math`](../library/math.xhtml#module-math "math: Mathematical functions (sin() etc.).") module gained [`erf()`](../library/math.xhtml#math.erf "math.erf") and [`erfc()`](../library/math.xhtml#math.erfc "math.erfc") for the error function and the complementary error function, [`expm1()`](../library/math.xhtml#math.expm1 "math.expm1") which computes `e**x - 1` with more precision than using [`exp()`](../library/math.xhtml#math.exp "math.exp") and subtracting 1, [`gamma()`](../library/math.xhtml#math.gamma "math.gamma") for the Gamma function, and [`lgamma()`](../library/math.xhtml#math.lgamma "math.lgamma") for the natural log of the Gamma function. (Contributed by Mark Dickinson and nirinA raseliarison; [bpo-3366](https://bugs.python.org/issue3366) \[https://bugs.python.org/issue3366\].)
- The [`multiprocessing`](../library/multiprocessing.xhtml#module-multiprocessing "multiprocessing: Process-based parallelism.") module's `Manager*` classes can now be passed a callable that will be called whenever a subprocess is started, along with a set of arguments that will be passed to the callable. (Contributed by lekma; [bpo-5585](https://bugs.python.org/issue5585) \[https://bugs.python.org/issue5585\].)
The `Pool` class, which controls a pool of worker processes, now has an optional *maxtasksperchild* parameter. Worker processes will perform the specified number of tasks and then exit, causing the `Pool` to start a new worker. This is useful if tasks may leak memory or other resources, or if some tasks will cause the worker to become very large. (Contributed by Charles Cazabon; [bpo-6963](https://bugs.python.org/issue6963) \[https://bugs.python.org/issue6963\].)
- The [`nntplib`](../library/nntplib.xhtml#module-nntplib "nntplib: NNTP protocol client (requires sockets).") module now supports IPv6 addresses. (Contributed by Derek Morr; [bpo-1664](https://bugs.python.org/issue1664) \[https://bugs.python.org/issue1664\].)
- New functions: the [`os`](../library/os.xhtml#module-os "os: Miscellaneous operating system interfaces.") module wraps the following POSIX system calls: [`getresgid()`](../library/os.xhtml#os.getresgid "os.getresgid") and [`getresuid()`](../library/os.xhtml#os.getresuid "os.getresuid"), which return the real, effective, and saved GIDs and UIDs; [`setresgid()`](../library/os.xhtml#os.setresgid "os.setresgid") and [`setresuid()`](../library/os.xhtml#os.setresuid "os.setresuid"), which set real, effective, and saved GIDs and UIDs to new values; [`initgroups()`](../library/os.xhtml#os.initgroups "os.initgroups"), which initialize the group access list for the current process. (GID/UID functions contributed by Travis H.; [bpo-6508](https://bugs.python.org/issue6508) \[https://bugs.python.org/issue6508\]. Support for initgroups added by Jean-Paul Calderone; [bpo-7333](https://bugs.python.org/issue7333) \[https://bugs.python.org/issue7333\].)
The [`os.fork()`](../library/os.xhtml#os.fork "os.fork") function now re-initializes the import lock in the child process; this fixes problems on Solaris when [`fork()`](../library/os.xhtml#os.fork "os.fork")is called from a thread. (Fixed by Zsolt Cserna; [bpo-7242](https://bugs.python.org/issue7242) \[https://bugs.python.org/issue7242\].)
- In the [`os.path`](../library/os.path.xhtml#module-os.path "os.path: Operations on pathnames.") module, the [`normpath()`](../library/os.path.xhtml#os.path.normpath "os.path.normpath") and [`abspath()`](../library/os.path.xhtml#os.path.abspath "os.path.abspath") functions now preserve Unicode; if their input path is a Unicode string, the return value is also a Unicode string. ([`normpath()`](../library/os.path.xhtml#os.path.normpath "os.path.normpath") fixed by Matt Giuca in [bpo-5827](https://bugs.python.org/issue5827) \[https://bugs.python.org/issue5827\]; [`abspath()`](../library/os.path.xhtml#os.path.abspath "os.path.abspath") fixed by Ezio Melotti in [bpo-3426](https://bugs.python.org/issue3426) \[https://bugs.python.org/issue3426\].)
- The [`pydoc`](../library/pydoc.xhtml#module-pydoc "pydoc: Documentation generator and online help system.") module now has help for the various symbols that Python uses. You can now do `help('<<')` or `help('@')`, for example. (Contributed by David Laban; [bpo-4739](https://bugs.python.org/issue4739) \[https://bugs.python.org/issue4739\].)
- The [`re`](../library/re.xhtml#module-re "re: Regular expression operations.") module's [`split()`](../library/re.xhtml#re.split "re.split"), [`sub()`](../library/re.xhtml#re.sub "re.sub"), and [`subn()`](../library/re.xhtml#re.subn "re.subn")now accept an optional *flags* argument, for consistency with the other functions in the module. (Added by Gregory P. Smith.)
- New function: [`run_path()`](../library/runpy.xhtml#runpy.run_path "runpy.run_path") in the [`runpy`](../library/runpy.xhtml#module-runpy "runpy: Locate and run Python modules without importing them first.") module will execute the code at a provided *path* argument. *path* can be the path of a Python source file (`example.py`), a compiled bytecode file (`example.pyc`), a directory (`./package/`), or a zip archive (`example.zip`). If a directory or zip path is provided, it will be added to the front of `sys.path` and the module [`__main__`](../library/__main__.xhtml#module-__main__ "__main__: The environment where the top-level script is run.") will be imported. It's expected that the directory or zip contains a `__main__.py`; if it doesn't, some other `__main__.py` might be imported from a location later in `sys.path`. This makes more of the machinery of [`runpy`](../library/runpy.xhtml#module-runpy "runpy: Locate and run Python modules without importing them first.") available to scripts that want to mimic the way Python's command line processes an explicit path name. (Added by Nick Coghlan; [bpo-6816](https://bugs.python.org/issue6816) \[https://bugs.python.org/issue6816\].)
- New function: in the [`shutil`](../library/shutil.xhtml#module-shutil "shutil: High-level file operations, including copying.") module, [`make_archive()`](../library/shutil.xhtml#shutil.make_archive "shutil.make_archive")takes a filename, archive type (zip or tar-format), and a directory path, and creates an archive containing the directory's contents. (Added by Tarek Ziadé.)
[`shutil`](../library/shutil.xhtml#module-shutil "shutil: High-level file operations, including copying.")'s [`copyfile()`](../library/shutil.xhtml#shutil.copyfile "shutil.copyfile") and [`copytree()`](../library/shutil.xhtml#shutil.copytree "shutil.copytree")functions now raise a `SpecialFileError` exception when asked to copy a named pipe. Previously the code would treat named pipes like a regular file by opening them for reading, and this would block indefinitely. (Fixed by Antoine Pitrou; [bpo-3002](https://bugs.python.org/issue3002) \[https://bugs.python.org/issue3002\].)
- The [`signal`](../library/signal.xhtml#module-signal "signal: Set handlers for asynchronous events.") module no longer re-installs the signal handler unless this is truly necessary, which fixes a bug that could make it impossible to catch the EINTR signal robustly. (Fixed by Charles-Francois Natali; [bpo-8354](https://bugs.python.org/issue8354) \[https://bugs.python.org/issue8354\].)
- New functions: in the [`site`](../library/site.xhtml#module-site "site: Module responsible for site-specific configuration.") module, three new functions return various site- and user-specific paths. [`getsitepackages()`](../library/site.xhtml#site.getsitepackages "site.getsitepackages") returns a list containing all global site-packages directories, [`getusersitepackages()`](../library/site.xhtml#site.getusersitepackages "site.getusersitepackages") returns the path of the user's site-packages directory, and [`getuserbase()`](../library/site.xhtml#site.getuserbase "site.getuserbase") returns the value of the `USER_BASE`environment variable, giving the path to a directory that can be used to store data. (Contributed by Tarek Ziadé; [bpo-6693](https://bugs.python.org/issue6693) \[https://bugs.python.org/issue6693\].)
The [`site`](../library/site.xhtml#module-site "site: Module responsible for site-specific configuration.") module now reports exceptions occurring when the `sitecustomize` module is imported, and will no longer catch and swallow the [`KeyboardInterrupt`](../library/exceptions.xhtml#KeyboardInterrupt "KeyboardInterrupt") exception. (Fixed by Victor Stinner; [bpo-3137](https://bugs.python.org/issue3137) \[https://bugs.python.org/issue3137\].)
- The [`create_connection()`](../library/socket.xhtml#socket.create_connection "socket.create_connection") function gained a *source\_address* parameter, a `(host, port)` 2-tuple giving the source address that will be used for the connection. (Contributed by Eldon Ziegler; [bpo-3972](https://bugs.python.org/issue3972) \[https://bugs.python.org/issue3972\].)
The [`recv_into()`](../library/socket.xhtml#socket.socket.recv_into "socket.socket.recv_into") and [`recvfrom_into()`](../library/socket.xhtml#socket.socket.recvfrom_into "socket.socket.recvfrom_into")methods will now write into objects that support the buffer API, most usefully the [`bytearray`](../library/stdtypes.xhtml#bytearray "bytearray") and [`memoryview`](../library/stdtypes.xhtml#memoryview "memoryview") objects. (Implemented by Antoine Pitrou; [bpo-8104](https://bugs.python.org/issue8104) \[https://bugs.python.org/issue8104\].)
- The `SocketServer` module's `TCPServer` class now supports socket timeouts and disabling the Nagle algorithm. The `disable_nagle_algorithm` class attribute defaults to `False`; if overridden to be true, new request connections will have the TCP\_NODELAY option set to prevent buffering many small sends into a single TCP packet. The `timeout` class attribute can hold a timeout in seconds that will be applied to the request socket; if no request is received within that time, `handle_timeout()`will be called and `handle_request()` will return. (Contributed by Kristján Valur Jónsson; [bpo-6192](https://bugs.python.org/issue6192) \[https://bugs.python.org/issue6192\] and [bpo-6267](https://bugs.python.org/issue6267) \[https://bugs.python.org/issue6267\].)
- Updated module: the [`sqlite3`](../library/sqlite3.xhtml#module-sqlite3 "sqlite3: A DB-API 2.0 implementation using SQLite 3.x.") module has been updated to version 2.6.0 of the [pysqlite package](https://github.com/ghaering/pysqlite) \[https://github.com/ghaering/pysqlite\]. Version 2.6.0 includes a number of bugfixes, and adds the ability to load SQLite extensions from shared libraries. Call the `enable_load_extension(True)` method to enable extensions, and then call [`load_extension()`](../library/sqlite3.xhtml#sqlite3.Connection.load_extension "sqlite3.Connection.load_extension") to load a particular shared library. (Updated by Gerhard H?ring.)
- The [`ssl`](../library/ssl.xhtml#module-ssl "ssl: TLS/SSL wrapper for socket objects") module's [`SSLSocket`](../library/ssl.xhtml#ssl.SSLSocket "ssl.SSLSocket") objects now support the buffer API, which fixed a test suite failure (fix by Antoine Pitrou; [bpo-7133](https://bugs.python.org/issue7133) \[https://bugs.python.org/issue7133\]) and automatically set OpenSSL's `SSL_MODE_AUTO_RETRY`, which will prevent an error code being returned from `recv()` operations that trigger an SSL renegotiation (fix by Antoine Pitrou; [bpo-8222](https://bugs.python.org/issue8222) \[https://bugs.python.org/issue8222\]).
The [`ssl.wrap_socket()`](../library/ssl.xhtml#ssl.wrap_socket "ssl.wrap_socket") constructor function now takes a *ciphers* argument that's a string listing the encryption algorithms to be allowed; the format of the string is described [in the OpenSSL documentation](https://www.openssl.org/docs/manmaster/man1/ciphers.html#CIPHER-LIST-FORMAT) \[https://www.openssl.org/docs/manmaster/man1/ciphers.html#CIPHER-LIST-FORMAT\]. (Added by Antoine Pitrou; [bpo-8322](https://bugs.python.org/issue8322) \[https://bugs.python.org/issue8322\].)
Another change makes the extension load all of OpenSSL's ciphers and digest algorithms so that they're all available. Some SSL certificates couldn't be verified, reporting an "unknown algorithm" error. (Reported by Beda Kosata, and fixed by Antoine Pitrou; [bpo-8484](https://bugs.python.org/issue8484) \[https://bugs.python.org/issue8484\].)
The version of OpenSSL being used is now available as the module attributes [`ssl.OPENSSL_VERSION`](../library/ssl.xhtml#ssl.OPENSSL_VERSION "ssl.OPENSSL_VERSION") (a string), [`ssl.OPENSSL_VERSION_INFO`](../library/ssl.xhtml#ssl.OPENSSL_VERSION_INFO "ssl.OPENSSL_VERSION_INFO") (a 5-tuple), and [`ssl.OPENSSL_VERSION_NUMBER`](../library/ssl.xhtml#ssl.OPENSSL_VERSION_NUMBER "ssl.OPENSSL_VERSION_NUMBER") (an integer). (Added by Antoine Pitrou; [bpo-8321](https://bugs.python.org/issue8321) \[https://bugs.python.org/issue8321\].)
- The [`struct`](../library/struct.xhtml#module-struct "struct: Interpret bytes as packed binary data.") module will no longer silently ignore overflow errors when a value is too large for a particular integer format code (one of `bBhHiIlLqQ`); it now always raises a [`struct.error`](../library/struct.xhtml#struct.error "struct.error") exception. (Changed by Mark Dickinson; [bpo-1523](https://bugs.python.org/issue1523) \[https://bugs.python.org/issue1523\].) The [`pack()`](../library/struct.xhtml#struct.pack "struct.pack") function will also attempt to use [`__index__()`](../reference/datamodel.xhtml#object.__index__ "object.__index__") to convert and pack non-integers before trying the [`__int__()`](../reference/datamodel.xhtml#object.__int__ "object.__int__") method or reporting an error. (Changed by Mark Dickinson; [bpo-8300](https://bugs.python.org/issue8300) \[https://bugs.python.org/issue8300\].)
- New function: the [`subprocess`](../library/subprocess.xhtml#module-subprocess "subprocess: Subprocess management.") module's [`check_output()`](../library/subprocess.xhtml#subprocess.check_output "subprocess.check_output") runs a command with a specified set of arguments and returns the command's output as a string when the command runs without error, or raises a [`CalledProcessError`](../library/subprocess.xhtml#subprocess.CalledProcessError "subprocess.CalledProcessError") exception otherwise.
```
>>> subprocess.check_output(['df', '-h', '.'])
'Filesystem Size Used Avail Capacity Mounted on\n
/dev/disk0s2 52G 49G 3.0G 94% /\n'
>>> subprocess.check_output(['df', '-h', '/bogus'])
...
subprocess.CalledProcessError: Command '['df', '-h', '/bogus']' returned non-zero exit status 1
```
(Contributed by Gregory P. Smith.)
The [`subprocess`](../library/subprocess.xhtml#module-subprocess "subprocess: Subprocess management.") module will now retry its internal system calls on receiving an `EINTR` signal. (Reported by several people; final patch by Gregory P. Smith in [bpo-1068268](https://bugs.python.org/issue1068268) \[https://bugs.python.org/issue1068268\].)
- New function: [`is_declared_global()`](../library/symtable.xhtml#symtable.Symbol.is_declared_global "symtable.Symbol.is_declared_global") in the [`symtable`](../library/symtable.xhtml#module-symtable "symtable: Interface to the compiler's internal symbol tables.") module returns true for variables that are explicitly declared to be global, false for ones that are implicitly global. (Contributed by Jeremy Hylton.)
- The [`syslog`](../library/syslog.xhtml#module-syslog "syslog: An interface to the Unix syslog library routines. (Unix)") module will now use the value of `sys.argv[0]` as the identifier instead of the previous default value of `'python'`. (Changed by Sean Reifschneider; [bpo-8451](https://bugs.python.org/issue8451) \[https://bugs.python.org/issue8451\].)
- The `sys.version_info` value is now a named tuple, with attributes named `major`, `minor`, `micro`, `releaselevel`, and `serial`. (Contributed by Ross Light; [bpo-4285](https://bugs.python.org/issue4285) \[https://bugs.python.org/issue4285\].)
[`sys.getwindowsversion()`](../library/sys.xhtml#sys.getwindowsversion "sys.getwindowsversion") also returns a named tuple, with attributes named `major`, `minor`, `build`, [`platform`](../library/platform.xhtml#module-platform "platform: Retrieves as much platform identifying data as possible."), `service_pack`, `service_pack_major`, `service_pack_minor`, `suite_mask`, and `product_type`. (Contributed by Brian Curtin; [bpo-7766](https://bugs.python.org/issue7766) \[https://bugs.python.org/issue7766\].)
- The [`tarfile`](../library/tarfile.xhtml#module-tarfile "tarfile: Read and write tar-format archive files.") module's default error handling has changed, to no longer suppress fatal errors. The default error level was previously 0, which meant that errors would only result in a message being written to the debug log, but because the debug log is not activated by default, these errors go unnoticed. The default error level is now 1, which raises an exception if there's an error. (Changed by Lars Gust?bel; [bpo-7357](https://bugs.python.org/issue7357) \[https://bugs.python.org/issue7357\].)
[`tarfile`](../library/tarfile.xhtml#module-tarfile "tarfile: Read and write tar-format archive files.") now supports filtering the [`TarInfo`](../library/tarfile.xhtml#tarfile.TarInfo "tarfile.TarInfo")objects being added to a tar file. When you call [`add()`](../library/tarfile.xhtml#tarfile.TarFile.add "tarfile.TarFile.add"), you may supply an optional *filter* argument that's a callable. The *filter* callable will be passed the [`TarInfo`](../library/tarfile.xhtml#tarfile.TarInfo "tarfile.TarInfo") for every file being added, and can modify and return it. If the callable returns `None`, the file will be excluded from the resulting archive. This is more powerful than the existing *exclude* argument, which has therefore been deprecated. (Added by Lars Gust?bel; [bpo-6856](https://bugs.python.org/issue6856) \[https://bugs.python.org/issue6856\].) The [`TarFile`](../library/tarfile.xhtml#tarfile.TarFile "tarfile.TarFile") class also now supports the context management protocol. (Added by Lars Gust?bel; [bpo-7232](https://bugs.python.org/issue7232) \[https://bugs.python.org/issue7232\].)
- The [`wait()`](../library/threading.xhtml#threading.Event.wait "threading.Event.wait") method of the [`threading.Event`](../library/threading.xhtml#threading.Event "threading.Event") class now returns the internal flag on exit. This means the method will usually return true because [`wait()`](../library/threading.xhtml#threading.Event.wait "threading.Event.wait") is supposed to block until the internal flag becomes true. The return value will only be false if a timeout was provided and the operation timed out. (Contributed by Tim Lesher; [bpo-1674032](https://bugs.python.org/issue1674032) \[https://bugs.python.org/issue1674032\].)
- The Unicode database provided by the [`unicodedata`](../library/unicodedata.xhtml#module-unicodedata "unicodedata: Access the Unicode Database.") module is now used internally to determine which characters are numeric, whitespace, or represent line breaks. The database also includes information from the `Unihan.txt` data file (patch by Anders Chrigstr?m and Amaury Forgeot d'Arc; [bpo-1571184](https://bugs.python.org/issue1571184) \[https://bugs.python.org/issue1571184\]) and has been updated to version 5.2.0 (updated by Florent Xicluna; [bpo-8024](https://bugs.python.org/issue8024) \[https://bugs.python.org/issue8024\]).
- The `urlparse` module's `urlsplit()` now handles unknown URL schemes in a fashion compliant with [**RFC 3986**](https://tools.ietf.org/html/rfc3986.html) \[https://tools.ietf.org/html/rfc3986.html\]: if the URL is of the form `"<something>://..."`, the text before the `://` is treated as the scheme, even if it's a made-up scheme that the module doesn't know about. This change may break code that worked around the old behaviour. For example, Python 2.6.4 or 2.5 will return the following:
```
>>> import urlparse
>>> urlparse.urlsplit('invented://host/filename?query')
('invented', '', '//host/filename?query', '', '')
```
Python 2.7 (and Python 2.6.5) will return:
```
>>> import urlparse
>>> urlparse.urlsplit('invented://host/filename?query')
('invented', 'host', '/filename?query', '', '')
```
(Python 2.7 actually produces slightly different output, since it returns a named tuple instead of a standard tuple.)
The `urlparse` module also supports IPv6 literal addresses as defined by [**RFC 2732**](https://tools.ietf.org/html/rfc2732.html) \[https://tools.ietf.org/html/rfc2732.html\] (contributed by Senthil Kumaran; [bpo-2987](https://bugs.python.org/issue2987) \[https://bugs.python.org/issue2987\]).
```
>>> urlparse.urlparse('http://[1080::8:800:200C:417A]/foo')
ParseResult(scheme='http', netloc='[1080::8:800:200C:417A]',
path='/foo', params='', query='', fragment='')
```
- New class: the [`WeakSet`](../library/weakref.xhtml#weakref.WeakSet "weakref.WeakSet") class in the [`weakref`](../library/weakref.xhtml#module-weakref "weakref: Support for weak references and weak dictionaries.")module is a set that only holds weak references to its elements; elements will be removed once there are no references pointing to them. (Originally implemented in Python 3.x by Raymond Hettinger, and backported to 2.7 by Michael Foord.)
- The ElementTree library, `xml.etree`, no longer escapes ampersands and angle brackets when outputting an XML processing instruction (which looks like `<?xml-stylesheet href="#style1"?>`) or comment (which looks like `\<!-- comment -->`). (Patch by Neil Muller; [bpo-2746](https://bugs.python.org/issue2746) \[https://bugs.python.org/issue2746\].)
- The XML-RPC client and server, provided by the `xmlrpclib` and `SimpleXMLRPCServer` modules, have improved performance by supporting HTTP/1.1 keep-alive and by optionally using gzip encoding to compress the XML being exchanged. The gzip compression is controlled by the `encode_threshold` attribute of `SimpleXMLRPCRequestHandler`, which contains a size in bytes; responses larger than this will be compressed. (Contributed by Kristján Valur Jónsson; [bpo-6267](https://bugs.python.org/issue6267) \[https://bugs.python.org/issue6267\].)
- The [`zipfile`](../library/zipfile.xhtml#module-zipfile "zipfile: Read and write ZIP-format archive files.") module's [`ZipFile`](../library/zipfile.xhtml#zipfile.ZipFile "zipfile.ZipFile") now supports the context management protocol, so you can write `with zipfile.ZipFile(...) as f:`. (Contributed by Brian Curtin; [bpo-5511](https://bugs.python.org/issue5511) \[https://bugs.python.org/issue5511\].)
[`zipfile`](../library/zipfile.xhtml#module-zipfile "zipfile: Read and write ZIP-format archive files.") now also supports archiving empty directories and extracts them correctly. (Fixed by Kuba Wieczorek; [bpo-4710](https://bugs.python.org/issue4710) \[https://bugs.python.org/issue4710\].) Reading files out of an archive is faster, and interleaving [`read()`](../library/zipfile.xhtml#zipfile.ZipFile.read "zipfile.ZipFile.read") and `readline()` now works correctly. (Contributed by Nir Aides; [bpo-7610](https://bugs.python.org/issue7610) \[https://bugs.python.org/issue7610\].)
The [`is_zipfile()`](../library/zipfile.xhtml#zipfile.is_zipfile "zipfile.is_zipfile") function now accepts a file object, in addition to the path names accepted in earlier versions. (Contributed by Gabriel Genellina; [bpo-4756](https://bugs.python.org/issue4756) \[https://bugs.python.org/issue4756\].)
The [`writestr()`](../library/zipfile.xhtml#zipfile.ZipFile.writestr "zipfile.ZipFile.writestr") method now has an optional *compress\_type* parameter that lets you override the default compression method specified in the [`ZipFile`](../library/zipfile.xhtml#zipfile.ZipFile "zipfile.ZipFile") constructor. (Contributed by Ronald Oussoren; [bpo-6003](https://bugs.python.org/issue6003) \[https://bugs.python.org/issue6003\].)
### New module: importlib
Python 3.1 includes the [`importlib`](../library/importlib.xhtml#module-importlib "importlib: The implementation of the import machinery.") package, a re-implementation of the logic underlying Python's [`import`](../reference/simple_stmts.xhtml#import) statement. [`importlib`](../library/importlib.xhtml#module-importlib "importlib: The implementation of the import machinery.") is useful for implementors of Python interpreters and to users who wish to write new importers that can participate in the import process. Python 2.7 doesn't contain the complete [`importlib`](../library/importlib.xhtml#module-importlib "importlib: The implementation of the import machinery.") package, but instead has a tiny subset that contains a single function, [`import_module()`](../library/importlib.xhtml#importlib.import_module "importlib.import_module").
`import_module(name, package=None)` imports a module. *name* is a string containing the module or package's name. It's possible to do relative imports by providing a string that begins with a `.`character, such as `..utils.errors`. For relative imports, the *package* argument must be provided and is the name of the package that will be used as the anchor for the relative import. [`import_module()`](../library/importlib.xhtml#importlib.import_module "importlib.import_module") both inserts the imported module into `sys.modules` and returns the module object.
Here are some examples:
```
>>> from importlib import import_module
>>> anydbm = import_module('anydbm') # Standard absolute import
>>> anydbm
<module 'anydbm' from '/p/python/Lib/anydbm.py'>
>>> # Relative import
>>> file_util = import_module('..file_util', 'distutils.command')
>>> file_util
<module 'distutils.file_util' from '/python/Lib/distutils/file_util.pyc'>
```
[`importlib`](../library/importlib.xhtml#module-importlib "importlib: The implementation of the import machinery.") was implemented by Brett Cannon and introduced in Python 3.1.
### New module: sysconfig
The [`sysconfig`](../library/sysconfig.xhtml#module-sysconfig "sysconfig: Python's configuration information") module has been pulled out of the Distutils package, becoming a new top-level module in its own right. [`sysconfig`](../library/sysconfig.xhtml#module-sysconfig "sysconfig: Python's configuration information") provides functions for getting information about Python's build process: compiler switches, installation paths, the platform name, and whether Python is running from its source directory.
Some of the functions in the module are:
- [`get_config_var()`](../library/sysconfig.xhtml#sysconfig.get_config_var "sysconfig.get_config_var") returns variables from Python's Makefile and the `pyconfig.h` file.
- [`get_config_vars()`](../library/sysconfig.xhtml#sysconfig.get_config_vars "sysconfig.get_config_vars") returns a dictionary containing all of the configuration variables.
- [`get_path()`](../library/sysconfig.xhtml#sysconfig.get_path "sysconfig.get_path") returns the configured path for a particular type of module: the standard library, site-specific modules, platform-specific modules, etc.
- [`is_python_build()`](../library/sysconfig.xhtml#sysconfig.is_python_build "sysconfig.is_python_build") returns true if you're running a binary from a Python source tree, and false otherwise.
Consult the [`sysconfig`](../library/sysconfig.xhtml#module-sysconfig "sysconfig: Python's configuration information") documentation for more details and for a complete list of functions.
The Distutils package and [`sysconfig`](../library/sysconfig.xhtml#module-sysconfig "sysconfig: Python's configuration information") are now maintained by Tarek Ziadé, who has also started a Distutils2 package (source repository at <https://hg.python.org/distutils2/>) for developing a next-generation version of Distutils.
### ttk: Themed Widgets for Tk
Tcl/Tk 8.5 includes a set of themed widgets that re-implement basic Tk widgets but have a more customizable appearance and can therefore more closely resemble the native platform's widgets. This widget set was originally called Tile, but was renamed to Ttk (for "themed Tk") on being added to Tcl/Tck release 8.5.
To learn more, read the `ttk` module documentation. You may also wish to read the Tcl/Tk manual page describing the Ttk theme engine, available at [https://www.tcl.tk/man/tcl8.5/TkCmd/ttk\_intro.htm](https://www.tcl.tk/man/tcl8.5/TkCmd/ttk_intro.htm). Some screenshots of the Python/Ttk code in use are at <https://code.google.com/archive/p/python-ttk/wikis/Screenshots.wiki>.
The `ttk` module was written by Guilherme Polo and added in [bpo-2983](https://bugs.python.org/issue2983) \[https://bugs.python.org/issue2983\]. An alternate version called `Tile.py`, written by Martin Franklin and maintained by Kevin Walzer, was proposed for inclusion in [bpo-2618](https://bugs.python.org/issue2618) \[https://bugs.python.org/issue2618\], but the authors argued that Guilherme Polo's work was more comprehensive.
### Updated module: unittest
The [`unittest`](../library/unittest.xhtml#module-unittest "unittest: Unit testing framework for Python.") module was greatly enhanced; many new features were added. Most of these features were implemented by Michael Foord, unless otherwise noted. The enhanced version of the module is downloadable separately for use with Python versions 2.4 to 2.6, packaged as the `unittest2` package, from <https://pypi.org/project/unittest2>.
When used from the command line, the module can automatically discover tests. It's not as fancy as [py.test](http://pytest.org) \[http://pytest.org\] or [nose](https://nose.readthedocs.io/) \[https://nose.readthedocs.io/\], but provides a simple way to run tests kept within a set of package directories. For example, the following command will search the `test/` subdirectory for any importable test files named `test*.py`:
```
python -m unittest discover -s test
```
Consult the [`unittest`](../library/unittest.xhtml#module-unittest "unittest: Unit testing framework for Python.") module documentation for more details. (Developed in [bpo-6001](https://bugs.python.org/issue6001) \[https://bugs.python.org/issue6001\].)
The [`main()`](../library/unittest.xhtml#unittest.main "unittest.main") function supports some other new options:
- [`-b`](../library/unittest.xhtml#cmdoption-unittest-b) or `--buffer` will buffer the standard output and standard error streams during each test. If the test passes, any resulting output will be discarded; on failure, the buffered output will be displayed.
- [`-c`](../library/unittest.xhtml#cmdoption-unittest-c) or `--catch` will cause the control-C interrupt to be handled more gracefully. Instead of interrupting the test process immediately, the currently running test will be completed and then the partial results up to the interruption will be reported. If you're impatient, a second press of control-C will cause an immediate interruption.
This control-C handler tries to avoid causing problems when the code being tested or the tests being run have defined a signal handler of their own, by noticing that a signal handler was already set and calling it. If this doesn't work for you, there's a [`removeHandler()`](../library/unittest.xhtml#unittest.removeHandler "unittest.removeHandler") decorator that can be used to mark tests that should have the control-C handling disabled.
- [`-f`](../library/unittest.xhtml#cmdoption-unittest-f) or `--failfast` makes test execution stop immediately when a test fails instead of continuing to execute further tests. (Suggested by Cliff Dyer and implemented by Michael Foord; [bpo-8074](https://bugs.python.org/issue8074) \[https://bugs.python.org/issue8074\].)
The progress messages now show 'x' for expected failures and 'u' for unexpected successes when run in verbose mode. (Contributed by Benjamin Peterson.)
Test cases can raise the [`SkipTest`](../library/unittest.xhtml#unittest.SkipTest "unittest.SkipTest") exception to skip a test ([bpo-1034053](https://bugs.python.org/issue1034053) \[https://bugs.python.org/issue1034053\]).
The error messages for [`assertEqual()`](../library/unittest.xhtml#unittest.TestCase.assertEqual "unittest.TestCase.assertEqual"), [`assertTrue()`](../library/unittest.xhtml#unittest.TestCase.assertTrue "unittest.TestCase.assertTrue"), and [`assertFalse()`](../library/unittest.xhtml#unittest.TestCase.assertFalse "unittest.TestCase.assertFalse")failures now provide more information. If you set the [`longMessage`](../library/unittest.xhtml#unittest.TestCase.longMessage "unittest.TestCase.longMessage") attribute of your [`TestCase`](../library/unittest.xhtml#unittest.TestCase "unittest.TestCase") classes to true, both the standard error message and any additional message you provide will be printed for failures. (Added by Michael Foord; [bpo-5663](https://bugs.python.org/issue5663) \[https://bugs.python.org/issue5663\].)
The [`assertRaises()`](../library/unittest.xhtml#unittest.TestCase.assertRaises "unittest.TestCase.assertRaises") method now returns a context handler when called without providing a callable object to run. For example, you can write this:
```
with self.assertRaises(KeyError):
{}['foo']
```
(Implemented by Antoine Pitrou; [bpo-4444](https://bugs.python.org/issue4444) \[https://bugs.python.org/issue4444\].)
Module- and class-level setup and teardown fixtures are now supported. Modules can contain `setUpModule()` and `tearDownModule()`functions. Classes can have [`setUpClass()`](../library/unittest.xhtml#unittest.TestCase.setUpClass "unittest.TestCase.setUpClass") and [`tearDownClass()`](../library/unittest.xhtml#unittest.TestCase.tearDownClass "unittest.TestCase.tearDownClass") methods that must be defined as class methods (using `@classmethod` or equivalent). These functions and methods are invoked when the test runner switches to a test case in a different module or class.
The methods [`addCleanup()`](../library/unittest.xhtml#unittest.TestCase.addCleanup "unittest.TestCase.addCleanup") and [`doCleanups()`](../library/unittest.xhtml#unittest.TestCase.doCleanups "unittest.TestCase.doCleanups") were added. [`addCleanup()`](../library/unittest.xhtml#unittest.TestCase.addCleanup "unittest.TestCase.addCleanup") lets you add cleanup functions that will be called unconditionally (after [`setUp()`](../library/unittest.xhtml#unittest.TestCase.setUp "unittest.TestCase.setUp") if [`setUp()`](../library/unittest.xhtml#unittest.TestCase.setUp "unittest.TestCase.setUp") fails, otherwise after [`tearDown()`](../library/unittest.xhtml#unittest.TestCase.tearDown "unittest.TestCase.tearDown")). This allows for much simpler resource allocation and deallocation during tests ([bpo-5679](https://bugs.python.org/issue5679) \[https://bugs.python.org/issue5679\]).
A number of new methods were added that provide more specialized tests. Many of these methods were written by Google engineers for use in their test suites; Gregory P. Smith, Michael Foord, and GvR worked on merging them into Python's version of [`unittest`](../library/unittest.xhtml#module-unittest "unittest: Unit testing framework for Python.").
- [`assertIsNone()`](../library/unittest.xhtml#unittest.TestCase.assertIsNone "unittest.TestCase.assertIsNone") and [`assertIsNotNone()`](../library/unittest.xhtml#unittest.TestCase.assertIsNotNone "unittest.TestCase.assertIsNotNone") take one expression and verify that the result is or is not `None`.
- [`assertIs()`](../library/unittest.xhtml#unittest.TestCase.assertIs "unittest.TestCase.assertIs") and [`assertIsNot()`](../library/unittest.xhtml#unittest.TestCase.assertIsNot "unittest.TestCase.assertIsNot")take two values and check whether the two values evaluate to the same object or not. (Added by Michael Foord; [bpo-2578](https://bugs.python.org/issue2578) \[https://bugs.python.org/issue2578\].)
- [`assertIsInstance()`](../library/unittest.xhtml#unittest.TestCase.assertIsInstance "unittest.TestCase.assertIsInstance") and [`assertNotIsInstance()`](../library/unittest.xhtml#unittest.TestCase.assertNotIsInstance "unittest.TestCase.assertNotIsInstance") check whether the resulting object is an instance of a particular class, or of one of a tuple of classes. (Added by Georg Brandl; [bpo-7031](https://bugs.python.org/issue7031) \[https://bugs.python.org/issue7031\].)
- [`assertGreater()`](../library/unittest.xhtml#unittest.TestCase.assertGreater "unittest.TestCase.assertGreater"), [`assertGreaterEqual()`](../library/unittest.xhtml#unittest.TestCase.assertGreaterEqual "unittest.TestCase.assertGreaterEqual"), [`assertLess()`](../library/unittest.xhtml#unittest.TestCase.assertLess "unittest.TestCase.assertLess"), and [`assertLessEqual()`](../library/unittest.xhtml#unittest.TestCase.assertLessEqual "unittest.TestCase.assertLessEqual") compare two quantities.
- [`assertMultiLineEqual()`](../library/unittest.xhtml#unittest.TestCase.assertMultiLineEqual "unittest.TestCase.assertMultiLineEqual") compares two strings, and if they're not equal, displays a helpful comparison that highlights the differences in the two strings. This comparison is now used by default when Unicode strings are compared with [`assertEqual()`](../library/unittest.xhtml#unittest.TestCase.assertEqual "unittest.TestCase.assertEqual").
- `assertRegexpMatches()` and `assertNotRegexpMatches()` checks whether the first argument is a string matching or not matching the regular expression provided as the second argument ([bpo-8038](https://bugs.python.org/issue8038) \[https://bugs.python.org/issue8038\]).
- `assertRaisesRegexp()` checks whether a particular exception is raised, and then also checks that the string representation of the exception matches the provided regular expression.
- [`assertIn()`](../library/unittest.xhtml#unittest.TestCase.assertIn "unittest.TestCase.assertIn") and [`assertNotIn()`](../library/unittest.xhtml#unittest.TestCase.assertNotIn "unittest.TestCase.assertNotIn")tests whether *first* is or is not in *second*.
- `assertItemsEqual()` tests whether two provided sequences contain the same elements.
- [`assertSetEqual()`](../library/unittest.xhtml#unittest.TestCase.assertSetEqual "unittest.TestCase.assertSetEqual") compares whether two sets are equal, and only reports the differences between the sets in case of error.
- Similarly, [`assertListEqual()`](../library/unittest.xhtml#unittest.TestCase.assertListEqual "unittest.TestCase.assertListEqual") and [`assertTupleEqual()`](../library/unittest.xhtml#unittest.TestCase.assertTupleEqual "unittest.TestCase.assertTupleEqual")compare the specified types and explain any differences without necessarily printing their full values; these methods are now used by default when comparing lists and tuples using [`assertEqual()`](../library/unittest.xhtml#unittest.TestCase.assertEqual "unittest.TestCase.assertEqual"). More generally, [`assertSequenceEqual()`](../library/unittest.xhtml#unittest.TestCase.assertSequenceEqual "unittest.TestCase.assertSequenceEqual") compares two sequences and can optionally check whether both sequences are of a particular type.
- [`assertDictEqual()`](../library/unittest.xhtml#unittest.TestCase.assertDictEqual "unittest.TestCase.assertDictEqual") compares two dictionaries and reports the differences; it's now used by default when you compare two dictionaries using [`assertEqual()`](../library/unittest.xhtml#unittest.TestCase.assertEqual "unittest.TestCase.assertEqual"). `assertDictContainsSubset()` checks whether all of the key/value pairs in *first* are found in *second*.
- [`assertAlmostEqual()`](../library/unittest.xhtml#unittest.TestCase.assertAlmostEqual "unittest.TestCase.assertAlmostEqual") and [`assertNotAlmostEqual()`](../library/unittest.xhtml#unittest.TestCase.assertNotAlmostEqual "unittest.TestCase.assertNotAlmostEqual") test whether *first* and *second* are approximately equal. This method can either round their difference to an optionally-specified number of *places* (the default is 7) and compare it to zero, or require the difference to be smaller than a supplied *delta* value.
- [`loadTestsFromName()`](../library/unittest.xhtml#unittest.TestLoader.loadTestsFromName "unittest.TestLoader.loadTestsFromName") properly honors the [`suiteClass`](../library/unittest.xhtml#unittest.TestLoader.suiteClass "unittest.TestLoader.suiteClass") attribute of the [`TestLoader`](../library/unittest.xhtml#unittest.TestLoader "unittest.TestLoader"). (Fixed by Mark Roddy; [bpo-6866](https://bugs.python.org/issue6866) \[https://bugs.python.org/issue6866\].)
- A new hook lets you extend the [`assertEqual()`](../library/unittest.xhtml#unittest.TestCase.assertEqual "unittest.TestCase.assertEqual") method to handle new data types. The [`addTypeEqualityFunc()`](../library/unittest.xhtml#unittest.TestCase.addTypeEqualityFunc "unittest.TestCase.addTypeEqualityFunc") method takes a type object and a function. The function will be used when both of the objects being compared are of the specified type. This function should compare the two objects and raise an exception if they don't match; it's a good idea for the function to provide additional information about why the two objects aren't matching, much as the new sequence comparison methods do.
[`unittest.main()`](../library/unittest.xhtml#unittest.main "unittest.main") now takes an optional `exit` argument. If false, [`main()`](../library/unittest.xhtml#unittest.main "unittest.main") doesn't call [`sys.exit()`](../library/sys.xhtml#sys.exit "sys.exit"), allowing [`main()`](../library/unittest.xhtml#unittest.main "unittest.main") to be used from the interactive interpreter. (Contributed by J. Pablo Fernández; [bpo-3379](https://bugs.python.org/issue3379) \[https://bugs.python.org/issue3379\].)
[`TestResult`](../library/unittest.xhtml#unittest.TestResult "unittest.TestResult") has new [`startTestRun()`](../library/unittest.xhtml#unittest.TestResult.startTestRun "unittest.TestResult.startTestRun") and [`stopTestRun()`](../library/unittest.xhtml#unittest.TestResult.stopTestRun "unittest.TestResult.stopTestRun") methods that are called immediately before and after a test run. (Contributed by Robert Collins; [bpo-5728](https://bugs.python.org/issue5728) \[https://bugs.python.org/issue5728\].)
With all these changes, the `unittest.py` was becoming awkwardly large, so the module was turned into a package and the code split into several files (by Benjamin Peterson). This doesn't affect how the module is imported or used.
參見
<http://www.voidspace.org.uk/python/articles/unittest2.shtml>Describes the new features, how to use them, and the rationale for various design decisions. (By Michael Foord.)
### Updated module: ElementTree 1.3
The version of the ElementTree library included with Python was updated to version 1.3. Some of the new features are:
- The various parsing functions now take a *parser* keyword argument giving an [`XMLParser`](../library/xml.etree.elementtree.xhtml#xml.etree.ElementTree.XMLParser "xml.etree.ElementTree.XMLParser") instance that will be used. This makes it possible to override the file's internal encoding:
```
p = ET.XMLParser(encoding='utf-8')
t = ET.XML("""<root/>""", parser=p)
```
Errors in parsing XML now raise a `ParseError` exception, whose instances have a `position` attribute containing a (*line*, *column*) tuple giving the location of the problem.
- ElementTree's code for converting trees to a string has been significantly reworked, making it roughly twice as fast in many cases. The [`ElementTree.write()`](../library/xml.etree.elementtree.xhtml#xml.etree.ElementTree.ElementTree.write "xml.etree.ElementTree.ElementTree.write")and `Element.write()` methods now have a *method* parameter that can be "xml" (the default), "html", or "text". HTML mode will output empty elements as `<empty></empty>` instead of `<empty/>`, and text mode will skip over elements and only output the text chunks. If you set the `tag` attribute of an element to `None` but leave its children in place, the element will be omitted when the tree is written out, so you don't need to do more extensive rearrangement to remove a single element.
Namespace handling has also been improved. All `xmlns:<whatever>`declarations are now output on the root element, not scattered throughout the resulting XML. You can set the default namespace for a tree by setting the `default_namespace` attribute and can register new prefixes with [`register_namespace()`](../library/xml.etree.elementtree.xhtml#xml.etree.ElementTree.register_namespace "xml.etree.ElementTree.register_namespace"). In XML mode, you can use the true/false *xml\_declaration* parameter to suppress the XML declaration.
- New [`Element`](../library/xml.etree.elementtree.xhtml#xml.etree.ElementTree.Element "xml.etree.ElementTree.Element") method: [`extend()`](../library/xml.etree.elementtree.xhtml#xml.etree.ElementTree.Element.extend "xml.etree.ElementTree.Element.extend") appends the items from a sequence to the element's children. Elements themselves behave like sequences, so it's easy to move children from one element to another:
```
from xml.etree import ElementTree as ET
t = ET.XML("""<list>
<item>1</item> <item>2</item> <item>3</item>
</list>""")
new = ET.XML('<root/>')
new.extend(t)
# Outputs <root><item>1</item>...</root>
print ET.tostring(new)
```
- New `Element` method: [`iter()`](../library/xml.etree.elementtree.xhtml#xml.etree.ElementTree.Element.iter "xml.etree.ElementTree.Element.iter") yields the children of the element as a generator. It's also possible to write
```
for child in
elem:
```
to loop over an element's children. The existing method `getiterator()` is now deprecated, as is `getchildren()`which constructs and returns a list of children.
- New `Element` method: [`itertext()`](../library/xml.etree.elementtree.xhtml#xml.etree.ElementTree.Element.itertext "xml.etree.ElementTree.Element.itertext") yields all chunks of text that are descendants of the element. For example:
```
t = ET.XML("""<list>
<item>1</item> <item>2</item> <item>3</item>
</list>""")
# Outputs ['\n ', '1', ' ', '2', ' ', '3', '\n']
print list(t.itertext())
```
- Deprecated: using an element as a Boolean (i.e., `if elem:`) would return true if the element had any children, or false if there were no children. This behaviour is confusing -- `None` is false, but so is a childless element? -- so it will now trigger a [`FutureWarning`](../library/exceptions.xhtml#FutureWarning "FutureWarning"). In your code, you should be explicit: write `len(elem) != 0` if you're interested in the number of children, or `elem is not None`.
Fredrik Lundh develops ElementTree and produced the 1.3 version; you can read his article describing 1.3 at <http://effbot.org/zone/elementtree-13-intro.htm>. Florent Xicluna updated the version included with Python, after discussions on python-dev and in [bpo-6472](https://bugs.python.org/issue6472) \[https://bugs.python.org/issue6472\].)
## Build and C API Changes
Changes to Python's build process and to the C API include:
- The latest release of the GNU Debugger, GDB 7, can be [scripted using Python](https://sourceware.org/gdb/current/onlinedocs/gdb/Python.html) \[https://sourceware.org/gdb/current/onlinedocs/gdb/Python.html\]. When you begin debugging an executable program P, GDB will look for a file named `P-gdb.py` and automatically read it. Dave Malcolm contributed a `python-gdb.py` that adds a number of commands useful when debugging Python itself. For example, `py-up` and `py-down` go up or down one Python stack frame, which usually corresponds to several C stack frames. `py-print`prints the value of a Python variable, and `py-bt` prints the Python stack trace. (Added as a result of [bpo-8032](https://bugs.python.org/issue8032) \[https://bugs.python.org/issue8032\].)
- If you use the `.gdbinit` file provided with Python, the "pyo" macro in the 2.7 version now works correctly when the thread being debugged doesn't hold the GIL; the macro now acquires it before printing. (Contributed by Victor Stinner; [bpo-3632](https://bugs.python.org/issue3632) \[https://bugs.python.org/issue3632\].)
- [`Py_AddPendingCall()`](../c-api/init.xhtml#c.Py_AddPendingCall "Py_AddPendingCall") is now thread-safe, letting any worker thread submit notifications to the main Python thread. This is particularly useful for asynchronous IO operations. (Contributed by Kristján Valur Jónsson; [bpo-4293](https://bugs.python.org/issue4293) \[https://bugs.python.org/issue4293\].)
- New function: [`PyCode_NewEmpty()`](../c-api/code.xhtml#c.PyCode_NewEmpty "PyCode_NewEmpty") creates an empty code object; only the filename, function name, and first line number are required. This is useful for extension modules that are attempting to construct a more useful traceback stack. Previously such extensions needed to call [`PyCode_New()`](../c-api/code.xhtml#c.PyCode_New "PyCode_New"), which had many more arguments. (Added by Jeffrey Yasskin.)
- New function: [`PyErr_NewExceptionWithDoc()`](../c-api/exceptions.xhtml#c.PyErr_NewExceptionWithDoc "PyErr_NewExceptionWithDoc") creates a new exception class, just as the existing [`PyErr_NewException()`](../c-api/exceptions.xhtml#c.PyErr_NewException "PyErr_NewException") does, but takes an extra `char *` argument containing the docstring for the new exception class. (Added by 'lekma' on the Python bug tracker; [bpo-7033](https://bugs.python.org/issue7033) \[https://bugs.python.org/issue7033\].)
- New function: [`PyFrame_GetLineNumber()`](../c-api/reflection.xhtml#c.PyFrame_GetLineNumber "PyFrame_GetLineNumber") takes a frame object and returns the line number that the frame is currently executing. Previously code would need to get the index of the bytecode instruction currently executing, and then look up the line number corresponding to that address. (Added by Jeffrey Yasskin.)
- New functions: [`PyLong_AsLongAndOverflow()`](../c-api/long.xhtml#c.PyLong_AsLongAndOverflow "PyLong_AsLongAndOverflow") and [`PyLong_AsLongLongAndOverflow()`](../c-api/long.xhtml#c.PyLong_AsLongLongAndOverflow "PyLong_AsLongLongAndOverflow") approximates a Python long integer as a C `long` or `long long`. If the number is too large to fit into the output type, an *overflow* flag is set and returned to the caller. (Contributed by Case Van Horsen; [bpo-7528](https://bugs.python.org/issue7528) \[https://bugs.python.org/issue7528\] and [bpo-7767](https://bugs.python.org/issue7767) \[https://bugs.python.org/issue7767\].)
- New function: stemming from the rewrite of string-to-float conversion, a new [`PyOS_string_to_double()`](../c-api/conversion.xhtml#c.PyOS_string_to_double "PyOS_string_to_double") function was added. The old `PyOS_ascii_strtod()` and `PyOS_ascii_atof()` functions are now deprecated.
- New function: [`PySys_SetArgvEx()`](../c-api/init.xhtml#c.PySys_SetArgvEx "PySys_SetArgvEx") sets the value of `sys.argv` and can optionally update `sys.path` to include the directory containing the script named by `sys.argv[0]` depending on the value of an *updatepath* parameter.
This function was added to close a security hole for applications that embed Python. The old function, [`PySys_SetArgv()`](../c-api/init.xhtml#c.PySys_SetArgv "PySys_SetArgv"), would always update `sys.path`, and sometimes it would add the current directory. This meant that, if you ran an application embedding Python in a directory controlled by someone else, attackers could put a Trojan-horse module in the directory (say, a file named `os.py`) that your application would then import and run.
If you maintain a C/C++ application that embeds Python, check whether you're calling [`PySys_SetArgv()`](../c-api/init.xhtml#c.PySys_SetArgv "PySys_SetArgv") and carefully consider whether the application should be using [`PySys_SetArgvEx()`](../c-api/init.xhtml#c.PySys_SetArgvEx "PySys_SetArgvEx")with *updatepath* set to false.
Security issue reported as [CVE-2008-5983](https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2008-5983) \[https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2008-5983\]; discussed in [bpo-5753](https://bugs.python.org/issue5753) \[https://bugs.python.org/issue5753\], and fixed by Antoine Pitrou.
- New macros: the Python header files now define the following macros: `Py_ISALNUM`, `Py_ISALPHA`, `Py_ISDIGIT`, `Py_ISLOWER`, `Py_ISSPACE`, `Py_ISUPPER`, `Py_ISXDIGIT`, `Py_TOLOWER`, and `Py_TOUPPER`. All of these functions are analogous to the C standard macros for classifying characters, but ignore the current locale setting, because in several places Python needs to analyze characters in a locale-independent way. (Added by Eric Smith; [bpo-5793](https://bugs.python.org/issue5793) \[https://bugs.python.org/issue5793\].)
- Removed function: `PyEval_CallObject` is now only available as a macro. A function version was being kept around to preserve ABI linking compatibility, but that was in 1997; it can certainly be deleted by now. (Removed by Antoine Pitrou; [bpo-8276](https://bugs.python.org/issue8276) \[https://bugs.python.org/issue8276\].)
- New format codes: the `PyFormat_FromString()`, `PyFormat_FromStringV()`, and [`PyErr_Format()`](../c-api/exceptions.xhtml#c.PyErr_Format "PyErr_Format") functions now accept `%lld` and `%llu` format codes for displaying C's `long long` types. (Contributed by Mark Dickinson; [bpo-7228](https://bugs.python.org/issue7228) \[https://bugs.python.org/issue7228\].)
- The complicated interaction between threads and process forking has been changed. Previously, the child process created by [`os.fork()`](../library/os.xhtml#os.fork "os.fork") might fail because the child is created with only a single thread running, the thread performing the [`os.fork()`](../library/os.xhtml#os.fork "os.fork"). If other threads were holding a lock, such as Python's import lock, when the fork was performed, the lock would still be marked as "held" in the new process. But in the child process nothing would ever release the lock, since the other threads weren't replicated, and the child process would no longer be able to perform imports.
Python 2.7 acquires the import lock before performing an [`os.fork()`](../library/os.xhtml#os.fork "os.fork"), and will also clean up any locks created using the [`threading`](../library/threading.xhtml#module-threading "threading: Thread-based parallelism.") module. C extension modules that have internal locks, or that call `fork()` themselves, will not benefit from this clean-up.
(Fixed by Thomas Wouters; [bpo-1590864](https://bugs.python.org/issue1590864) \[https://bugs.python.org/issue1590864\].)
- The [`Py_Finalize()`](../c-api/init.xhtml#c.Py_Finalize "Py_Finalize") function now calls the internal `threading._shutdown()` function; this prevents some exceptions from being raised when an interpreter shuts down. (Patch by Adam Olsen; [bpo-1722344](https://bugs.python.org/issue1722344) \[https://bugs.python.org/issue1722344\].)
- When using the [`PyMemberDef`](../c-api/structures.xhtml#c.PyMemberDef "PyMemberDef") structure to define attributes of a type, Python will no longer let you try to delete or set a `T_STRING_INPLACE` attribute.
- Global symbols defined by the [`ctypes`](../library/ctypes.xhtml#module-ctypes "ctypes: A foreign function library for Python.") module are now prefixed with `Py`, or with `_ctypes`. (Implemented by Thomas Heller; [bpo-3102](https://bugs.python.org/issue3102) \[https://bugs.python.org/issue3102\].)
- New configure option: the `--with-system-expat` switch allows building the `pyexpat` module to use the system Expat library. (Contributed by Arfrever Frehtes Taifersar Arahesis; [bpo-7609](https://bugs.python.org/issue7609) \[https://bugs.python.org/issue7609\].)
- New configure option: the `--with-valgrind` option will now disable the pymalloc allocator, which is difficult for the Valgrind memory-error detector to analyze correctly. Valgrind will therefore be better at detecting memory leaks and overruns. (Contributed by James Henstridge; [bpo-2422](https://bugs.python.org/issue2422) \[https://bugs.python.org/issue2422\].)
- New configure option: you can now supply an empty string to `--with-dbmliborder=` in order to disable all of the various DBM modules. (Added by Arfrever Frehtes Taifersar Arahesis; [bpo-6491](https://bugs.python.org/issue6491) \[https://bugs.python.org/issue6491\].)
- The **configure** script now checks for floating-point rounding bugs on certain 32-bit Intel chips and defines a `X87_DOUBLE_ROUNDING`preprocessor definition. No code currently uses this definition, but it's available if anyone wishes to use it. (Added by Mark Dickinson; [bpo-2937](https://bugs.python.org/issue2937) \[https://bugs.python.org/issue2937\].)
**configure** also now sets a `LDCXXSHARED` Makefile variable for supporting C++ linking. (Contributed by Arfrever Frehtes Taifersar Arahesis; [bpo-1222585](https://bugs.python.org/issue1222585) \[https://bugs.python.org/issue1222585\].)
- The build process now creates the necessary files for pkg-config support. (Contributed by Clinton Roy; [bpo-3585](https://bugs.python.org/issue3585) \[https://bugs.python.org/issue3585\].)
- The build process now supports Subversion 1.7. (Contributed by Arfrever Frehtes Taifersar Arahesis; [bpo-6094](https://bugs.python.org/issue6094) \[https://bugs.python.org/issue6094\].)
### 膠囊
Python 3.1 adds a new C datatype, [`PyCapsule`](../c-api/capsule.xhtml#c.PyCapsule "PyCapsule"), for providing a C API to an extension module. A capsule is essentially the holder of a C `void *` pointer, and is made available as a module attribute; for example, the [`socket`](../library/socket.xhtml#module-socket "socket: Low-level networking interface.") module's API is exposed as `socket.CAPI`, and [`unicodedata`](../library/unicodedata.xhtml#module-unicodedata "unicodedata: Access the Unicode Database.") exposes `ucnhash_CAPI`. Other extensions can import the module, access its dictionary to get the capsule object, and then get the `void *` pointer, which will usually point to an array of pointers to the module's various API functions.
There is an existing data type already used for this, `PyCObject`, but it doesn't provide type safety. Evil code written in pure Python could cause a segmentation fault by taking a `PyCObject` from module A and somehow substituting it for the `PyCObject` in module B. Capsules know their own name, and getting the pointer requires providing the name:
```
void *vtable;
if (!PyCapsule_IsValid(capsule, "mymodule.CAPI") {
PyErr_SetString(PyExc_ValueError, "argument type invalid");
return NULL;
}
vtable = PyCapsule_GetPointer(capsule, "mymodule.CAPI");
```
You are assured that `vtable` points to whatever you're expecting. If a different capsule was passed in, [`PyCapsule_IsValid()`](../c-api/capsule.xhtml#c.PyCapsule_IsValid "PyCapsule_IsValid") would detect the mismatched name and return false. Refer to [給擴展模塊提供C API](../extending/extending.xhtml#using-capsules) for more information on using these objects.
Python 2.7 now uses capsules internally to provide various extension-module APIs, but the `PyCObject_AsVoidPtr()` was modified to handle capsules, preserving compile-time compatibility with the `CObject` interface. Use of `PyCObject_AsVoidPtr()` will signal a [`PendingDeprecationWarning`](../library/exceptions.xhtml#PendingDeprecationWarning "PendingDeprecationWarning"), which is silent by default.
Implemented in Python 3.1 and backported to 2.7 by Larry Hastings; discussed in [bpo-5630](https://bugs.python.org/issue5630) \[https://bugs.python.org/issue5630\].
### Port-Specific Changes: Windows
- The [`msvcrt`](../library/msvcrt.xhtml#module-msvcrt "msvcrt: Miscellaneous useful routines from the MS VC++ runtime. (Windows)") module now contains some constants from the `crtassem.h` header file: `CRT_ASSEMBLY_VERSION`, `VC_ASSEMBLY_PUBLICKEYTOKEN`, and `LIBRARIES_ASSEMBLY_NAME_PREFIX`. (Contributed by David Cournapeau; [bpo-4365](https://bugs.python.org/issue4365) \[https://bugs.python.org/issue4365\].)
- The `_winreg` module for accessing the registry now implements the `CreateKeyEx()` and `DeleteKeyEx()`functions, extended versions of previously-supported functions that take several extra arguments. The `DisableReflectionKey()`, `EnableReflectionKey()`, and `QueryReflectionKey()`were also tested and documented. (Implemented by Brian Curtin: [bpo-7347](https://bugs.python.org/issue7347) \[https://bugs.python.org/issue7347\].)
- The new `_beginthreadex()` API is used to start threads, and the native thread-local storage functions are now used. (Contributed by Kristján Valur Jónsson; [bpo-3582](https://bugs.python.org/issue3582) \[https://bugs.python.org/issue3582\].)
- The [`os.kill()`](../library/os.xhtml#os.kill "os.kill") function now works on Windows. The signal value can be the constants `CTRL_C_EVENT`, `CTRL_BREAK_EVENT`, or any integer. The first two constants will send Control-C and Control-Break keystroke events to subprocesses; any other value will use the `TerminateProcess()`API. (Contributed by Miki Tebeka; [bpo-1220212](https://bugs.python.org/issue1220212) \[https://bugs.python.org/issue1220212\].)
- The [`os.listdir()`](../library/os.xhtml#os.listdir "os.listdir") function now correctly fails for an empty path. (Fixed by Hirokazu Yamamoto; [bpo-5913](https://bugs.python.org/issue5913) \[https://bugs.python.org/issue5913\].)
- The `mimelib` module will now read the MIME database from the Windows registry when initializing. (Patch by Gabriel Genellina; [bpo-4969](https://bugs.python.org/issue4969) \[https://bugs.python.org/issue4969\].)
### Port-Specific Changes: Mac OS X
- The path `/Library/Python/2.7/site-packages` is now appended to `sys.path`, in order to share added packages between the system installation and a user-installed copy of the same version. (Changed by Ronald Oussoren; [bpo-4865](https://bugs.python.org/issue4865) \[https://bugs.python.org/issue4865\].)
> 在 2.7.13 版更改: As of 2.7.13, this change was removed. `/Library/Python/2.7/site-packages`, the site-packages directory used by the Apple-supplied system Python 2.7 is no longer appended to `sys.path` for user-installed Pythons such as from the python.org installers. As of macOS 10.12, Apple changed how the system site-packages directory is configured, which could cause installation of pip components, like setuptools, to fail. Packages installed for the system Python will no longer be shared with user-installed Pythons. ([bpo-28440](https://bugs.python.org/issue28440) \[https://bugs.python.org/issue28440\])
### Port-Specific Changes: FreeBSD
- FreeBSD 7.1's `SO_SETFIB` constant, used with `getsockopt()`/`setsockopt()` to select an alternate routing table, is now available in the [`socket`](../library/socket.xhtml#module-socket "socket: Low-level networking interface.")module. (Added by Kyle VanderBeek; [bpo-8235](https://bugs.python.org/issue8235) \[https://bugs.python.org/issue8235\].)
## Other Changes and Fixes
- Two benchmark scripts, `iobench` and `ccbench`, were added to the `Tools` directory. `iobench` measures the speed of the built-in file I/O objects returned by [`open()`](../library/functions.xhtml#open "open")while performing various operations, and `ccbench` is a concurrency benchmark that tries to measure computing throughput, thread switching latency, and IO processing bandwidth when performing several tasks using a varying number of threads.
- The `Tools/i18n/msgfmt.py` script now understands plural forms in `.po` files. (Fixed by Martin von L?wis; [bpo-5464](https://bugs.python.org/issue5464) \[https://bugs.python.org/issue5464\].)
- When importing a module from a `.pyc` or `.pyo` file with an existing `.py` counterpart, the `co_filename`attributes of the resulting code objects are overwritten when the original filename is obsolete. This can happen if the file has been renamed, moved, or is accessed through different paths. (Patch by Ziga Seilnacht and Jean-Paul Calderone; [bpo-1180193](https://bugs.python.org/issue1180193) \[https://bugs.python.org/issue1180193\].)
- The `regrtest.py` script now takes a `--randseed=`switch that takes an integer that will be used as the random seed for the `-r` option that executes tests in random order. The `-r` option also reports the seed that was used (Added by Collin Winter.)
- Another `regrtest.py` switch is `-j`, which takes an integer specifying how many tests run in parallel. This allows reducing the total runtime on multi-core machines. This option is compatible with several other options, including the `-R` switch which is known to produce long runtimes. (Added by Antoine Pitrou, [bpo-6152](https://bugs.python.org/issue6152) \[https://bugs.python.org/issue6152\].) This can also be used with a new `-F` switch that runs selected tests in a loop until they fail. (Added by Antoine Pitrou; [bpo-7312](https://bugs.python.org/issue7312) \[https://bugs.python.org/issue7312\].)
- When executed as a script, the `py_compile.py` module now accepts `'-'` as an argument, which will read standard input for the list of filenames to be compiled. (Contributed by Piotr O?arowski; [bpo-8233](https://bugs.python.org/issue8233) \[https://bugs.python.org/issue8233\].)
## Porting to Python 2.7
This section lists previously described changes and other bugfixes that may require changes to your code:
- The [`range()`](../library/stdtypes.xhtml#range "range") function processes its arguments more consistently; it will now call [`__int__()`](../reference/datamodel.xhtml#object.__int__ "object.__int__") on non-float, non-integer arguments that are supplied to it. (Fixed by Alexander Belopolsky; [bpo-1533](https://bugs.python.org/issue1533) \[https://bugs.python.org/issue1533\].)
- The string [`format()`](../library/functions.xhtml#format "format") method changed the default precision used for floating-point and complex numbers from 6 decimal places to 12, which matches the precision used by [`str()`](../library/stdtypes.xhtml#str "str"). (Changed by Eric Smith; [bpo-5920](https://bugs.python.org/issue5920) \[https://bugs.python.org/issue5920\].)
- Because of an optimization for the [`with`](../reference/compound_stmts.xhtml#with) statement, the special methods [`__enter__()`](../reference/datamodel.xhtml#object.__enter__ "object.__enter__") and [`__exit__()`](../reference/datamodel.xhtml#object.__exit__ "object.__exit__") must belong to the object's type, and cannot be directly attached to the object's instance. This affects new-style classes (derived from [`object`](../library/functions.xhtml#object "object")) and C extension types. ([bpo-6101](https://bugs.python.org/issue6101) \[https://bugs.python.org/issue6101\].)
- Due to a bug in Python 2.6, the *exc\_value* parameter to [`__exit__()`](../reference/datamodel.xhtml#object.__exit__ "object.__exit__") methods was often the string representation of the exception, not an instance. This was fixed in 2.7, so *exc\_value*will be an instance as expected. (Fixed by Florent Xicluna; [bpo-7853](https://bugs.python.org/issue7853) \[https://bugs.python.org/issue7853\].)
- When a restricted set of attributes were set using `__slots__`, deleting an unset attribute would not raise [`AttributeError`](../library/exceptions.xhtml#AttributeError "AttributeError")as you would expect. Fixed by Benjamin Peterson; [bpo-7604](https://bugs.python.org/issue7604) \[https://bugs.python.org/issue7604\].)
In the standard library:
- Operations with [`datetime`](../library/datetime.xhtml#datetime.datetime "datetime.datetime") instances that resulted in a year falling outside the supported range didn't always raise [`OverflowError`](../library/exceptions.xhtml#OverflowError "OverflowError"). Such errors are now checked more carefully and will now raise the exception. (Reported by Mark Leander, patch by Anand B. Pillai and Alexander Belopolsky; [bpo-7150](https://bugs.python.org/issue7150) \[https://bugs.python.org/issue7150\].)
- When using [`Decimal`](../library/decimal.xhtml#decimal.Decimal "decimal.Decimal") instances with a string's [`format()`](../library/functions.xhtml#format "format") method, the default alignment was previously left-alignment. This has been changed to right-alignment, which might change the output of your programs. (Changed by Mark Dickinson; [bpo-6857](https://bugs.python.org/issue6857) \[https://bugs.python.org/issue6857\].)
Comparisons involving a signaling NaN value (or `sNAN`) now signal [`InvalidOperation`](../library/decimal.xhtml#decimal.InvalidOperation "decimal.InvalidOperation") instead of silently returning a true or false value depending on the comparison operator. Quiet NaN values (or `NaN`) are now hashable. (Fixed by Mark Dickinson; [bpo-7279](https://bugs.python.org/issue7279) \[https://bugs.python.org/issue7279\].)
- The ElementTree library, `xml.etree`, no longer escapes ampersands and angle brackets when outputting an XML processing instruction (which looks like <?xml-stylesheet href="#style1"?>) or comment (which looks like \<!-- comment -->). (Patch by Neil Muller; [bpo-2746](https://bugs.python.org/issue2746) \[https://bugs.python.org/issue2746\].)
- The `readline()` method of `StringIO` objects now does nothing when a negative length is requested, as other file-like objects do. ([bpo-7348](https://bugs.python.org/issue7348) \[https://bugs.python.org/issue7348\]).
- The [`syslog`](../library/syslog.xhtml#module-syslog "syslog: An interface to the Unix syslog library routines. (Unix)") module will now use the value of `sys.argv[0]` as the identifier instead of the previous default value of `'python'`. (Changed by Sean Reifschneider; [bpo-8451](https://bugs.python.org/issue8451) \[https://bugs.python.org/issue8451\].)
- The [`tarfile`](../library/tarfile.xhtml#module-tarfile "tarfile: Read and write tar-format archive files.") module's default error handling has changed, to no longer suppress fatal errors. The default error level was previously 0, which meant that errors would only result in a message being written to the debug log, but because the debug log is not activated by default, these errors go unnoticed. The default error level is now 1, which raises an exception if there's an error. (Changed by Lars Gust?bel; [bpo-7357](https://bugs.python.org/issue7357) \[https://bugs.python.org/issue7357\].)
- The `urlparse` module's `urlsplit()` now handles unknown URL schemes in a fashion compliant with [**RFC 3986**](https://tools.ietf.org/html/rfc3986.html) \[https://tools.ietf.org/html/rfc3986.html\]: if the URL is of the form `"<something>://..."`, the text before the `://` is treated as the scheme, even if it's a made-up scheme that the module doesn't know about. This change may break code that worked around the old behaviour. For example, Python 2.6.4 or 2.5 will return the following:
```
>>> import urlparse
>>> urlparse.urlsplit('invented://host/filename?query')
('invented', '', '//host/filename?query', '', '')
```
Python 2.7 (and Python 2.6.5) will return:
```
>>> import urlparse
>>> urlparse.urlsplit('invented://host/filename?query')
('invented', 'host', '/filename?query', '', '')
```
(Python 2.7 actually produces slightly different output, since it returns a named tuple instead of a standard tuple.)
For C extensions:
- C extensions that use integer format codes with the `PyArg_Parse*`family of functions will now raise a [`TypeError`](../library/exceptions.xhtml#TypeError "TypeError") exception instead of triggering a [`DeprecationWarning`](../library/exceptions.xhtml#DeprecationWarning "DeprecationWarning") ([bpo-5080](https://bugs.python.org/issue5080) \[https://bugs.python.org/issue5080\]).
- Use the new [`PyOS_string_to_double()`](../c-api/conversion.xhtml#c.PyOS_string_to_double "PyOS_string_to_double") function instead of the old `PyOS_ascii_strtod()` and `PyOS_ascii_atof()` functions, which are now deprecated.
For applications that embed Python:
- The [`PySys_SetArgvEx()`](../c-api/init.xhtml#c.PySys_SetArgvEx "PySys_SetArgvEx") function was added, letting applications close a security hole when the existing [`PySys_SetArgv()`](../c-api/init.xhtml#c.PySys_SetArgv "PySys_SetArgv") function was used. Check whether you're calling [`PySys_SetArgv()`](../c-api/init.xhtml#c.PySys_SetArgv "PySys_SetArgv") and carefully consider whether the application should be using [`PySys_SetArgvEx()`](../c-api/init.xhtml#c.PySys_SetArgvEx "PySys_SetArgvEx") with *updatepath* set to false.
## New Features Added to Python 2.7 Maintenance Releases
New features may be added to Python 2.7 maintenance releases when the situation genuinely calls for it. Any such additions must go through the Python Enhancement Proposal process, and make a compelling case for why they can't be adequately addressed by either adding the new feature solely to Python 3, or else by publishing it on the Python Package Index.
In addition to the specific proposals listed below, there is a general exemption allowing new `-3` warnings to be added in any Python 2.7 maintenance release.
### Two new environment variables for debug mode
In debug mode, the `[xxx refs]` statistic is not written by default, the `PYTHONSHOWREFCOUNT` environment variable now must also be set. (Contributed by Victor Stinner; [bpo-31733](https://bugs.python.org/issue31733) \[https://bugs.python.org/issue31733\].)
When Python is compiled with `COUNT_ALLOC` defined, allocation counts are no longer dumped by default anymore: the `PYTHONSHOWALLOCCOUNT` environment variable must now also be set. Moreover, allocation counts are now dumped into stderr, rather than stdout. (Contributed by Victor Stinner; [bpo-31692](https://bugs.python.org/issue31692) \[https://bugs.python.org/issue31692\].)
2\.7.15 新版功能.
### PEP 434: IDLE Enhancement Exception for All Branches
[**PEP 434**](https://www.python.org/dev/peps/pep-0434) \[https://www.python.org/dev/peps/pep-0434\] describes a general exemption for changes made to the IDLE development environment shipped along with Python. This exemption makes it possible for the IDLE developers to provide a more consistent user experience across all supported versions of Python 2 and 3.
For details of any IDLE changes, refer to the NEWS file for the specific release.
### PEP 466: Network Security Enhancements for Python 2.7
[**PEP 466**](https://www.python.org/dev/peps/pep-0466) \[https://www.python.org/dev/peps/pep-0466\] describes a number of network security enhancement proposals that have been approved for inclusion in Python 2.7 maintenance releases, with the first of those changes appearing in the Python 2.7.7 release.
[**PEP 466**](https://www.python.org/dev/peps/pep-0466) \[https://www.python.org/dev/peps/pep-0466\] related features added in Python 2.7.7:
- [`hmac.compare_digest()`](../library/hmac.xhtml#hmac.compare_digest "hmac.compare_digest") was backported from Python 3 to make a timing attack resistant comparison operation available to Python 2 applications. (Contributed by Alex Gaynor; [bpo-21306](https://bugs.python.org/issue21306) \[https://bugs.python.org/issue21306\].)
- OpenSSL 1.0.1g was upgraded in the official Windows installers published on python.org. (Contributed by Zachary Ware; [bpo-21462](https://bugs.python.org/issue21462) \[https://bugs.python.org/issue21462\].)
[**PEP 466**](https://www.python.org/dev/peps/pep-0466) \[https://www.python.org/dev/peps/pep-0466\] related features added in Python 2.7.8:
- [`hashlib.pbkdf2_hmac()`](../library/hashlib.xhtml#hashlib.pbkdf2_hmac "hashlib.pbkdf2_hmac") was backported from Python 3 to make a hashing algorithm suitable for secure password storage broadly available to Python 2 applications. (Contributed by Alex Gaynor; [bpo-21304](https://bugs.python.org/issue21304) \[https://bugs.python.org/issue21304\].)
- OpenSSL 1.0.1h was upgraded for the official Windows installers published on python.org. (contributed by Zachary Ware in [bpo-21671](https://bugs.python.org/issue21671) \[https://bugs.python.org/issue21671\] for CVE-2014-0224)
[**PEP 466**](https://www.python.org/dev/peps/pep-0466) \[https://www.python.org/dev/peps/pep-0466\] related features added in Python 2.7.9:
- Most of Python 3.4's [`ssl`](../library/ssl.xhtml#module-ssl "ssl: TLS/SSL wrapper for socket objects") module was backported. This means [`ssl`](../library/ssl.xhtml#module-ssl "ssl: TLS/SSL wrapper for socket objects")now supports Server Name Indication, TLS1.x settings, access to the platform certificate store, the [`SSLContext`](../library/ssl.xhtml#ssl.SSLContext "ssl.SSLContext") class, and other features. (Contributed by Alex Gaynor and David Reid; [bpo-21308](https://bugs.python.org/issue21308) \[https://bugs.python.org/issue21308\].)
Refer to the "Version added: 2.7.9" notes in the module documentation for specific details.
- [`os.urandom()`](../library/os.xhtml#os.urandom "os.urandom") was changed to cache a file descriptor to `/dev/urandom`instead of reopening `/dev/urandom` on every call. (Contributed by Alex Gaynor; [bpo-21305](https://bugs.python.org/issue21305) \[https://bugs.python.org/issue21305\].)
- [`hashlib.algorithms_guaranteed`](../library/hashlib.xhtml#hashlib.algorithms_guaranteed "hashlib.algorithms_guaranteed") and [`hashlib.algorithms_available`](../library/hashlib.xhtml#hashlib.algorithms_available "hashlib.algorithms_available") were backported from Python 3 to make it easier for Python 2 applications to select the strongest available hash algorithm. (Contributed by Alex Gaynor in [bpo-21307](https://bugs.python.org/issue21307) \[https://bugs.python.org/issue21307\])
### PEP 477: Backport ensurepip (PEP 453) to Python 2.7
[**PEP 477**](https://www.python.org/dev/peps/pep-0477) \[https://www.python.org/dev/peps/pep-0477\] approves the inclusion of the [**PEP 453**](https://www.python.org/dev/peps/pep-0453) \[https://www.python.org/dev/peps/pep-0453\] ensurepip module and the improved documentation that was enabled by it in the Python 2.7 maintenance releases, appearing first in the Python 2.7.9 release.
#### Bootstrapping pip By Default
The new [`ensurepip`](../library/ensurepip.xhtml#module-ensurepip "ensurepip: Bootstrapping the "pip" installer into an existing Python installation or virtual environment.") module (defined in [**PEP 453**](https://www.python.org/dev/peps/pep-0453) \[https://www.python.org/dev/peps/pep-0453\]) provides a standard cross-platform mechanism to bootstrap the pip installer into Python installations. The version of `pip` included with Python 2.7.9 is `pip`1.5.6, and future 2.7.x maintenance releases will update the bundled version to the latest version of `pip` that is available at the time of creating the release candidate.
By default, the commands `pip`, `pipX` and `pipX.Y` will be installed on all platforms (where X.Y stands for the version of the Python installation), along with the `pip` Python package and its dependencies.
For CPython [source builds on POSIX systems](../using/unix.xhtml#building-python-on-unix), the `make install` and `make altinstall` commands do not bootstrap `pip`by default. This behaviour can be controlled through configure options, and overridden through Makefile options.
On Windows and Mac OS X, the CPython installers now default to installing `pip` along with CPython itself (users may opt out of installing it during the installation process). Window users will need to opt in to the automatic `PATH` modifications to have `pip` available from the command line by default, otherwise it can still be accessed through the Python launcher for Windows as `py -m pip`.
As [discussed in the PEP](https://www.python.org/dev/peps/pep-0477/#disabling-ensurepip-by-downstream-distributors) \[https://www.python.org/dev/peps/pep-0477/#disabling-ensurepip-by-downstream-distributors\], platform packagers may choose not to install these commands by default, as long as, when invoked, they provide clear and simple directions on how to install them on that platform (usually using the system package manager).
#### Documentation Changes
As part of this change, the [安裝 Python 模塊](../installing/index.xhtml#installing-index) and [分發 Python 模塊](../distributing/index.xhtml#distributing-index) sections of the documentation have been completely redesigned as short getting started and FAQ documents. Most packaging documentation has now been moved out to the Python Packaging Authority maintained [Python Packaging User Guide](http://packaging.python.org) \[http://packaging.python.org\] and the documentation of the individual projects.
However, as this migration is currently still incomplete, the legacy versions of those guides remaining available as [安裝Python模塊(舊版)](../install/index.xhtml#install-index)and [分發 Python 模塊(遺留版本)](../distutils/index.xhtml#distutils-index).
參見
[**PEP 453**](https://www.python.org/dev/peps/pep-0453) \[https://www.python.org/dev/peps/pep-0453\] -- Explicit bootstrapping of pip in Python installationsPEP written by Donald Stufft and Nick Coghlan, implemented by Donald Stufft, Nick Coghlan, Martin von L?wis and Ned Deily.
### PEP 476: Enabling certificate verification by default for stdlib http clients
[**PEP 476**](https://www.python.org/dev/peps/pep-0476) \[https://www.python.org/dev/peps/pep-0476\] updated `httplib` and modules which use it, such as `urllib2` and `xmlrpclib`, to now verify that the server presents a certificate which is signed by a Certificate Authority in the platform trust store and whose hostname matches the hostname being requested by default, significantly improving security for many applications. This change was made in the Python 2.7.9 release.
For applications which require the old previous behavior, they can pass an alternate context:
```
import urllib2
import ssl
# This disables all verification
context = ssl._create_unverified_context()
# This allows using a specific certificate for the host, which doesn't need
# to be in the trust store
context = ssl.create_default_context(cafile="/path/to/file.crt")
urllib2.urlopen("https://invalid-cert", context=context)
```
### PEP 493: HTTPS verification migration tools for Python 2.7
[**PEP 493**](https://www.python.org/dev/peps/pep-0493) \[https://www.python.org/dev/peps/pep-0493\] provides additional migration tools to support a more incremental infrastructure upgrade process for environments containing applications and services relying on the historically permissive processing of server certificates when establishing client HTTPS connections. These additions were made in the Python 2.7.12 release.
These tools are intended for use in cases where affected applications and services can't be modified to explicitly pass a more permissive SSL context when establishing the connection.
For applications and services which can't be modified at all, the new `PYTHONHTTPSVERIFY` environment variable may be set to `0` to revert an entire Python process back to the default permissive behaviour of Python 2.7.8 and earlier.
For cases where the connection establishment code can't be modified, but the overall application can be, the new `ssl._https_verify_certificates()`function can be used to adjust the default behaviour at runtime.
### New `make regen-all` build target
To simplify cross-compilation, and to ensure that CPython can reliably be compiled without requiring an existing version of Python to already be available, the autotools-based build system no longer attempts to implicitly recompile generated files based on file modification times.
Instead, a new `make regen-all` command has been added to force regeneration of these files when desired (e.g. after an initial version of Python has already been built based on the pregenerated versions).
More selective regeneration targets are also defined - see [Makefile.pre.in](https://github.com/python/cpython/tree/3.7/Makefile.pre.in) \[https://github.com/python/cpython/tree/3.7/Makefile.pre.in\] for details.
(Contributed by Victor Stinner in [bpo-23404](https://bugs.python.org/issue23404) \[https://bugs.python.org/issue23404\].)
2\.7.14 新版功能.
### Removal of `make touch` build target
The `make touch` build target previously used to request implicit regeneration of generated files by updating their modification times has been removed.
It has been replaced by the new `make regen-all` target.
(Contributed by Victor Stinner in [bpo-23404](https://bugs.python.org/issue23404) \[https://bugs.python.org/issue23404\].)
在 2.7.14 版更改.
## Acknowledgements
The author would like to thank the following people for offering suggestions, corrections and assistance with various drafts of this article: Nick Coghlan, Philip Jenvey, Ryan Lovett, R. David Murray, Hugh Secker-Walker.
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- [模塊](../py-modindex.xhtml "Python 模塊索引") |
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- Python文檔內容
- Python 有什么新變化?
- Python 3.7 有什么新變化
- 摘要 - 發布重點
- 新的特性
- 其他語言特性修改
- 新增模塊
- 改進的模塊
- C API 的改變
- 構建的改變
- 性能優化
- 其他 CPython 實現的改變
- 已棄用的 Python 行為
- 已棄用的 Python 模塊、函數和方法
- 已棄用的 C API 函數和類型
- 平臺支持的移除
- API 與特性的移除
- 移除的模塊
- Windows 專屬的改變
- 移植到 Python 3.7
- Python 3.7.1 中的重要變化
- Python 3.7.2 中的重要變化
- Python 3.6 有什么新變化A
- 摘要 - 發布重點
- 新的特性
- 其他語言特性修改
- 新增模塊
- 改進的模塊
- 性能優化
- Build and C API Changes
- 其他改進
- 棄用
- 移除
- 移植到Python 3.6
- Python 3.6.2 中的重要變化
- Python 3.6.4 中的重要變化
- Python 3.6.5 中的重要變化
- Python 3.6.7 中的重要變化
- Python 3.5 有什么新變化
- 摘要 - 發布重點
- 新的特性
- 其他語言特性修改
- 新增模塊
- 改進的模塊
- Other module-level changes
- 性能優化
- Build and C API Changes
- 棄用
- 移除
- Porting to Python 3.5
- Notable changes in Python 3.5.4
- What's New In Python 3.4
- 摘要 - 發布重點
- 新的特性
- 新增模塊
- 改進的模塊
- CPython Implementation Changes
- 棄用
- 移除
- Porting to Python 3.4
- Changed in 3.4.3
- What's New In Python 3.3
- 摘要 - 發布重點
- PEP 405: Virtual Environments
- PEP 420: Implicit Namespace Packages
- PEP 3118: New memoryview implementation and buffer protocol documentation
- PEP 393: Flexible String Representation
- PEP 397: Python Launcher for Windows
- PEP 3151: Reworking the OS and IO exception hierarchy
- PEP 380: Syntax for Delegating to a Subgenerator
- PEP 409: Suppressing exception context
- PEP 414: Explicit Unicode literals
- PEP 3155: Qualified name for classes and functions
- PEP 412: Key-Sharing Dictionary
- PEP 362: Function Signature Object
- PEP 421: Adding sys.implementation
- Using importlib as the Implementation of Import
- 其他語言特性修改
- A Finer-Grained Import Lock
- Builtin functions and types
- 新增模塊
- 改進的模塊
- 性能優化
- Build and C API Changes
- 棄用
- Porting to Python 3.3
- What's New In Python 3.2
- PEP 384: Defining a Stable ABI
- PEP 389: Argparse Command Line Parsing Module
- PEP 391: Dictionary Based Configuration for Logging
- PEP 3148: The concurrent.futures module
- PEP 3147: PYC Repository Directories
- PEP 3149: ABI Version Tagged .so Files
- PEP 3333: Python Web Server Gateway Interface v1.0.1
- 其他語言特性修改
- New, Improved, and Deprecated Modules
- 多線程
- 性能優化
- Unicode
- Codecs
- 文檔
- IDLE
- Code Repository
- Build and C API Changes
- Porting to Python 3.2
- What's New In Python 3.1
- PEP 372: Ordered Dictionaries
- PEP 378: Format Specifier for Thousands Separator
- 其他語言特性修改
- New, Improved, and Deprecated Modules
- 性能優化
- IDLE
- Build and C API Changes
- Porting to Python 3.1
- What's New In Python 3.0
- Common Stumbling Blocks
- Overview Of Syntax Changes
- Changes Already Present In Python 2.6
- Library Changes
- PEP 3101: A New Approach To String Formatting
- Changes To Exceptions
- Miscellaneous Other Changes
- Build and C API Changes
- 性能
- Porting To Python 3.0
- What's New in Python 2.7
- The Future for Python 2.x
- Changes to the Handling of Deprecation Warnings
- Python 3.1 Features
- PEP 372: Adding an Ordered Dictionary to collections
- PEP 378: Format Specifier for Thousands Separator
- PEP 389: The argparse Module for Parsing Command Lines
- PEP 391: Dictionary-Based Configuration For Logging
- PEP 3106: Dictionary Views
- PEP 3137: The memoryview Object
- 其他語言特性修改
- New and Improved Modules
- Build and C API Changes
- Other Changes and Fixes
- Porting to Python 2.7
- New Features Added to Python 2.7 Maintenance Releases
- Acknowledgements
- Python 2.6 有什么新變化
- Python 3.0
- Changes to the Development Process
- PEP 343: The 'with' statement
- PEP 366: Explicit Relative Imports From a Main Module
- PEP 370: Per-user site-packages Directory
- PEP 371: The multiprocessing Package
- PEP 3101: Advanced String Formatting
- PEP 3105: print As a Function
- PEP 3110: Exception-Handling Changes
- PEP 3112: Byte Literals
- PEP 3116: New I/O Library
- PEP 3118: Revised Buffer Protocol
- PEP 3119: Abstract Base Classes
- PEP 3127: Integer Literal Support and Syntax
- PEP 3129: Class Decorators
- PEP 3141: A Type Hierarchy for Numbers
- 其他語言特性修改
- New and Improved Modules
- Deprecations and Removals
- Build and C API Changes
- Porting to Python 2.6
- Acknowledgements
- What's New in Python 2.5
- PEP 308: Conditional Expressions
- PEP 309: Partial Function Application
- PEP 314: Metadata for Python Software Packages v1.1
- PEP 328: Absolute and Relative Imports
- PEP 338: Executing Modules as Scripts
- PEP 341: Unified try/except/finally
- PEP 342: New Generator Features
- PEP 343: The 'with' statement
- PEP 352: Exceptions as New-Style Classes
- PEP 353: Using ssize_t as the index type
- PEP 357: The 'index' method
- 其他語言特性修改
- New, Improved, and Removed Modules
- Build and C API Changes
- Porting to Python 2.5
- Acknowledgements
- What's New in Python 2.4
- PEP 218: Built-In Set Objects
- PEP 237: Unifying Long Integers and Integers
- PEP 289: Generator Expressions
- PEP 292: Simpler String Substitutions
- PEP 318: Decorators for Functions and Methods
- PEP 322: Reverse Iteration
- PEP 324: New subprocess Module
- PEP 327: Decimal Data Type
- PEP 328: Multi-line Imports
- PEP 331: Locale-Independent Float/String Conversions
- 其他語言特性修改
- New, Improved, and Deprecated Modules
- Build and C API Changes
- Porting to Python 2.4
- Acknowledgements
- What's New in Python 2.3
- PEP 218: A Standard Set Datatype
- PEP 255: Simple Generators
- PEP 263: Source Code Encodings
- PEP 273: Importing Modules from ZIP Archives
- PEP 277: Unicode file name support for Windows NT
- PEP 278: Universal Newline Support
- PEP 279: enumerate()
- PEP 282: The logging Package
- PEP 285: A Boolean Type
- PEP 293: Codec Error Handling Callbacks
- PEP 301: Package Index and Metadata for Distutils
- PEP 302: New Import Hooks
- PEP 305: Comma-separated Files
- PEP 307: Pickle Enhancements
- Extended Slices
- 其他語言特性修改
- New, Improved, and Deprecated Modules
- Pymalloc: A Specialized Object Allocator
- Build and C API Changes
- Other Changes and Fixes
- Porting to Python 2.3
- Acknowledgements
- What's New in Python 2.2
- 概述
- PEPs 252 and 253: Type and Class Changes
- PEP 234: Iterators
- PEP 255: Simple Generators
- PEP 237: Unifying Long Integers and Integers
- PEP 238: Changing the Division Operator
- Unicode Changes
- PEP 227: Nested Scopes
- New and Improved Modules
- Interpreter Changes and Fixes
- Other Changes and Fixes
- Acknowledgements
- What's New in Python 2.1
- 概述
- PEP 227: Nested Scopes
- PEP 236: future Directives
- PEP 207: Rich Comparisons
- PEP 230: Warning Framework
- PEP 229: New Build System
- PEP 205: Weak References
- PEP 232: Function Attributes
- PEP 235: Importing Modules on Case-Insensitive Platforms
- PEP 217: Interactive Display Hook
- PEP 208: New Coercion Model
- PEP 241: Metadata in Python Packages
- New and Improved Modules
- Other Changes and Fixes
- Acknowledgements
- What's New in Python 2.0
- 概述
- What About Python 1.6?
- New Development Process
- Unicode
- 列表推導式
- Augmented Assignment
- 字符串的方法
- Garbage Collection of Cycles
- Other Core Changes
- Porting to 2.0
- Extending/Embedding Changes
- Distutils: Making Modules Easy to Install
- XML Modules
- Module changes
- New modules
- IDLE Improvements
- Deleted and Deprecated Modules
- Acknowledgements
- 更新日志
- Python 下一版
- Python 3.7.3 最終版
- Python 3.7.3 發布候選版 1
- Python 3.7.2 最終版
- Python 3.7.2 發布候選版 1
- Python 3.7.1 最終版
- Python 3.7.1 RC 2版本
- Python 3.7.1 發布候選版 1
- Python 3.7.0 正式版
- Python 3.7.0 release candidate 1
- Python 3.7.0 beta 5
- Python 3.7.0 beta 4
- Python 3.7.0 beta 3
- Python 3.7.0 beta 2
- Python 3.7.0 beta 1
- Python 3.7.0 alpha 4
- Python 3.7.0 alpha 3
- Python 3.7.0 alpha 2
- Python 3.7.0 alpha 1
- Python 3.6.6 final
- Python 3.6.6 RC 1
- Python 3.6.5 final
- Python 3.6.5 release candidate 1
- Python 3.6.4 final
- Python 3.6.4 release candidate 1
- Python 3.6.3 final
- Python 3.6.3 release candidate 1
- Python 3.6.2 final
- Python 3.6.2 release candidate 2
- Python 3.6.2 release candidate 1
- Python 3.6.1 final
- Python 3.6.1 release candidate 1
- Python 3.6.0 final
- Python 3.6.0 release candidate 2
- Python 3.6.0 release candidate 1
- Python 3.6.0 beta 4
- Python 3.6.0 beta 3
- Python 3.6.0 beta 2
- Python 3.6.0 beta 1
- Python 3.6.0 alpha 4
- Python 3.6.0 alpha 3
- Python 3.6.0 alpha 2
- Python 3.6.0 alpha 1
- Python 3.5.5 final
- Python 3.5.5 release candidate 1
- Python 3.5.4 final
- Python 3.5.4 release candidate 1
- Python 3.5.3 final
- Python 3.5.3 release candidate 1
- Python 3.5.2 final
- Python 3.5.2 release candidate 1
- Python 3.5.1 final
- Python 3.5.1 release candidate 1
- Python 3.5.0 final
- Python 3.5.0 release candidate 4
- Python 3.5.0 release candidate 3
- Python 3.5.0 release candidate 2
- Python 3.5.0 release candidate 1
- Python 3.5.0 beta 4
- Python 3.5.0 beta 3
- Python 3.5.0 beta 2
- Python 3.5.0 beta 1
- Python 3.5.0 alpha 4
- Python 3.5.0 alpha 3
- Python 3.5.0 alpha 2
- Python 3.5.0 alpha 1
- Python 教程
- 課前甜點
- 使用 Python 解釋器
- 調用解釋器
- 解釋器的運行環境
- Python 的非正式介紹
- Python 作為計算器使用
- 走向編程的第一步
- 其他流程控制工具
- if 語句
- for 語句
- range() 函數
- break 和 continue 語句,以及循環中的 else 子句
- pass 語句
- 定義函數
- 函數定義的更多形式
- 小插曲:編碼風格
- 數據結構
- 列表的更多特性
- del 語句
- 元組和序列
- 集合
- 字典
- 循環的技巧
- 深入條件控制
- 序列和其它類型的比較
- 模塊
- 有關模塊的更多信息
- 標準模塊
- dir() 函數
- 包
- 輸入輸出
- 更漂亮的輸出格式
- 讀寫文件
- 錯誤和異常
- 語法錯誤
- 異常
- 處理異常
- 拋出異常
- 用戶自定義異常
- 定義清理操作
- 預定義的清理操作
- 類
- 名稱和對象
- Python 作用域和命名空間
- 初探類
- 補充說明
- 繼承
- 私有變量
- 雜項說明
- 迭代器
- 生成器
- 生成器表達式
- 標準庫簡介
- 操作系統接口
- 文件通配符
- 命令行參數
- 錯誤輸出重定向和程序終止
- 字符串模式匹配
- 數學
- 互聯網訪問
- 日期和時間
- 數據壓縮
- 性能測量
- 質量控制
- 自帶電池
- 標準庫簡介 —— 第二部分
- 格式化輸出
- 模板
- 使用二進制數據記錄格式
- 多線程
- 日志
- 弱引用
- 用于操作列表的工具
- 十進制浮點運算
- 虛擬環境和包
- 概述
- 創建虛擬環境
- 使用pip管理包
- 接下來?
- 交互式編輯和編輯歷史
- Tab 補全和編輯歷史
- 默認交互式解釋器的替代品
- 浮點算術:爭議和限制
- 表示性錯誤
- 附錄
- 交互模式
- 安裝和使用 Python
- 命令行與環境
- 命令行
- 環境變量
- 在Unix平臺中使用Python
- 獲取最新版本的Python
- 構建Python
- 與Python相關的路徑和文件
- 雜項
- 編輯器和集成開發環境
- 在Windows上使用 Python
- 完整安裝程序
- Microsoft Store包
- nuget.org 安裝包
- 可嵌入的包
- 替代捆綁包
- 配置Python
- 適用于Windows的Python啟動器
- 查找模塊
- 附加模塊
- 在Windows上編譯Python
- 其他平臺
- 在蘋果系統上使用 Python
- 獲取和安裝 MacPython
- IDE
- 安裝額外的 Python 包
- Mac 上的圖形界面編程
- 在 Mac 上分發 Python 應用程序
- 其他資源
- Python 語言參考
- 概述
- 其他實現
- 標注
- 詞法分析
- 行結構
- 其他形符
- 標識符和關鍵字
- 字面值
- 運算符
- 分隔符
- 數據模型
- 對象、值與類型
- 標準類型層級結構
- 特殊方法名稱
- 協程
- 執行模型
- 程序的結構
- 命名與綁定
- 異常
- 導入系統
- importlib
- 包
- 搜索
- 加載
- 基于路徑的查找器
- 替換標準導入系統
- Package Relative Imports
- 有關 main 的特殊事項
- 開放問題項
- 參考文獻
- 表達式
- 算術轉換
- 原子
- 原型
- await 表達式
- 冪運算符
- 一元算術和位運算
- 二元算術運算符
- 移位運算
- 二元位運算
- 比較運算
- 布爾運算
- 條件表達式
- lambda 表達式
- 表達式列表
- 求值順序
- 運算符優先級
- 簡單語句
- 表達式語句
- 賦值語句
- assert 語句
- pass 語句
- del 語句
- return 語句
- yield 語句
- raise 語句
- break 語句
- continue 語句
- import 語句
- global 語句
- nonlocal 語句
- 復合語句
- if 語句
- while 語句
- for 語句
- try 語句
- with 語句
- 函數定義
- 類定義
- 協程
- 最高層級組件
- 完整的 Python 程序
- 文件輸入
- 交互式輸入
- 表達式輸入
- 完整的語法規范
- Python 標準庫
- 概述
- 可用性注釋
- 內置函數
- 內置常量
- 由 site 模塊添加的常量
- 內置類型
- 邏輯值檢測
- 布爾運算 — and, or, not
- 比較
- 數字類型 — int, float, complex
- 迭代器類型
- 序列類型 — list, tuple, range
- 文本序列類型 — str
- 二進制序列類型 — bytes, bytearray, memoryview
- 集合類型 — set, frozenset
- 映射類型 — dict
- 上下文管理器類型
- 其他內置類型
- 特殊屬性
- 內置異常
- 基類
- 具體異常
- 警告
- 異常層次結構
- 文本處理服務
- string — 常見的字符串操作
- re — 正則表達式操作
- 模塊 difflib 是一個計算差異的助手
- textwrap — Text wrapping and filling
- unicodedata — Unicode 數據庫
- stringprep — Internet String Preparation
- readline — GNU readline interface
- rlcompleter — GNU readline的完成函數
- 二進制數據服務
- struct — Interpret bytes as packed binary data
- codecs — Codec registry and base classes
- 數據類型
- datetime — 基礎日期/時間數據類型
- calendar — General calendar-related functions
- collections — 容器數據類型
- collections.abc — 容器的抽象基類
- heapq — 堆隊列算法
- bisect — Array bisection algorithm
- array — Efficient arrays of numeric values
- weakref — 弱引用
- types — Dynamic type creation and names for built-in types
- copy — 淺層 (shallow) 和深層 (deep) 復制操作
- pprint — 數據美化輸出
- reprlib — Alternate repr() implementation
- enum — Support for enumerations
- 數字和數學模塊
- numbers — 數字的抽象基類
- math — 數學函數
- cmath — Mathematical functions for complex numbers
- decimal — 十進制定點和浮點運算
- fractions — 分數
- random — 生成偽隨機數
- statistics — Mathematical statistics functions
- 函數式編程模塊
- itertools — 為高效循環而創建迭代器的函數
- functools — 高階函數和可調用對象上的操作
- operator — 標準運算符替代函數
- 文件和目錄訪問
- pathlib — 面向對象的文件系統路徑
- os.path — 常見路徑操作
- fileinput — Iterate over lines from multiple input streams
- stat — Interpreting stat() results
- filecmp — File and Directory Comparisons
- tempfile — Generate temporary files and directories
- glob — Unix style pathname pattern expansion
- fnmatch — Unix filename pattern matching
- linecache — Random access to text lines
- shutil — High-level file operations
- macpath — Mac OS 9 路徑操作函數
- 數據持久化
- pickle —— Python 對象序列化
- copyreg — Register pickle support functions
- shelve — Python object persistence
- marshal — Internal Python object serialization
- dbm — Interfaces to Unix “databases”
- sqlite3 — SQLite 數據庫 DB-API 2.0 接口模塊
- 數據壓縮和存檔
- zlib — 與 gzip 兼容的壓縮
- gzip — 對 gzip 格式的支持
- bz2 — 對 bzip2 壓縮算法的支持
- lzma — 用 LZMA 算法壓縮
- zipfile — 在 ZIP 歸檔中工作
- tarfile — Read and write tar archive files
- 文件格式
- csv — CSV 文件讀寫
- configparser — Configuration file parser
- netrc — netrc file processing
- xdrlib — Encode and decode XDR data
- plistlib — Generate and parse Mac OS X .plist files
- 加密服務
- hashlib — 安全哈希與消息摘要
- hmac — 基于密鑰的消息驗證
- secrets — Generate secure random numbers for managing secrets
- 通用操作系統服務
- os — 操作系統接口模塊
- io — 處理流的核心工具
- time — 時間的訪問和轉換
- argparse — 命令行選項、參數和子命令解析器
- getopt — C-style parser for command line options
- 模塊 logging — Python 的日志記錄工具
- logging.config — 日志記錄配置
- logging.handlers — Logging handlers
- getpass — 便攜式密碼輸入工具
- curses — 終端字符單元顯示的處理
- curses.textpad — Text input widget for curses programs
- curses.ascii — Utilities for ASCII characters
- curses.panel — A panel stack extension for curses
- platform — Access to underlying platform's identifying data
- errno — Standard errno system symbols
- ctypes — Python 的外部函數庫
- 并發執行
- threading — 基于線程的并行
- multiprocessing — 基于進程的并行
- concurrent 包
- concurrent.futures — 啟動并行任務
- subprocess — 子進程管理
- sched — 事件調度器
- queue — 一個同步的隊列類
- _thread — 底層多線程 API
- _dummy_thread — _thread 的替代模塊
- dummy_threading — 可直接替代 threading 模塊。
- contextvars — Context Variables
- Context Variables
- Manual Context Management
- asyncio support
- 網絡和進程間通信
- asyncio — 異步 I/O
- socket — 底層網絡接口
- ssl — TLS/SSL wrapper for socket objects
- select — Waiting for I/O completion
- selectors — 高級 I/O 復用庫
- asyncore — 異步socket處理器
- asynchat — 異步 socket 指令/響應 處理器
- signal — Set handlers for asynchronous events
- mmap — Memory-mapped file support
- 互聯網數據處理
- email — 電子郵件與 MIME 處理包
- json — JSON 編碼和解碼器
- mailcap — Mailcap file handling
- mailbox — Manipulate mailboxes in various formats
- mimetypes — Map filenames to MIME types
- base64 — Base16, Base32, Base64, Base85 數據編碼
- binhex — 對binhex4文件進行編碼和解碼
- binascii — 二進制和 ASCII 碼互轉
- quopri — Encode and decode MIME quoted-printable data
- uu — Encode and decode uuencode files
- 結構化標記處理工具
- html — 超文本標記語言支持
- html.parser — 簡單的 HTML 和 XHTML 解析器
- html.entities — HTML 一般實體的定義
- XML處理模塊
- xml.etree.ElementTree — The ElementTree XML API
- xml.dom — The Document Object Model API
- xml.dom.minidom — Minimal DOM implementation
- xml.dom.pulldom — Support for building partial DOM trees
- xml.sax — Support for SAX2 parsers
- xml.sax.handler — Base classes for SAX handlers
- xml.sax.saxutils — SAX Utilities
- xml.sax.xmlreader — Interface for XML parsers
- xml.parsers.expat — Fast XML parsing using Expat
- 互聯網協議和支持
- webbrowser — 方便的Web瀏覽器控制器
- cgi — Common Gateway Interface support
- cgitb — Traceback manager for CGI scripts
- wsgiref — WSGI Utilities and Reference Implementation
- urllib — URL 處理模塊
- urllib.request — 用于打開 URL 的可擴展庫
- urllib.response — Response classes used by urllib
- urllib.parse — Parse URLs into components
- urllib.error — Exception classes raised by urllib.request
- urllib.robotparser — Parser for robots.txt
- http — HTTP 模塊
- http.client — HTTP協議客戶端
- ftplib — FTP protocol client
- poplib — POP3 protocol client
- imaplib — IMAP4 protocol client
- nntplib — NNTP protocol client
- smtplib —SMTP協議客戶端
- smtpd — SMTP Server
- telnetlib — Telnet client
- uuid — UUID objects according to RFC 4122
- socketserver — A framework for network servers
- http.server — HTTP 服務器
- http.cookies — HTTP state management
- http.cookiejar — Cookie handling for HTTP clients
- xmlrpc — XMLRPC 服務端與客戶端模塊
- xmlrpc.client — XML-RPC client access
- xmlrpc.server — Basic XML-RPC servers
- ipaddress — IPv4/IPv6 manipulation library
- 多媒體服務
- audioop — Manipulate raw audio data
- aifc — Read and write AIFF and AIFC files
- sunau — 讀寫 Sun AU 文件
- wave — 讀寫WAV格式文件
- chunk — Read IFF chunked data
- colorsys — Conversions between color systems
- imghdr — 推測圖像類型
- sndhdr — 推測聲音文件的類型
- ossaudiodev — Access to OSS-compatible audio devices
- 國際化
- gettext — 多語種國際化服務
- locale — 國際化服務
- 程序框架
- turtle — 海龜繪圖
- cmd — 支持面向行的命令解釋器
- shlex — Simple lexical analysis
- Tk圖形用戶界面(GUI)
- tkinter — Tcl/Tk的Python接口
- tkinter.ttk — Tk themed widgets
- tkinter.tix — Extension widgets for Tk
- tkinter.scrolledtext — 滾動文字控件
- IDLE
- 其他圖形用戶界面(GUI)包
- 開發工具
- typing — 類型標注支持
- pydoc — Documentation generator and online help system
- doctest — Test interactive Python examples
- unittest — 單元測試框架
- unittest.mock — mock object library
- unittest.mock 上手指南
- 2to3 - 自動將 Python 2 代碼轉為 Python 3 代碼
- test — Regression tests package for Python
- test.support — Utilities for the Python test suite
- test.support.script_helper — Utilities for the Python execution tests
- 調試和分析
- bdb — Debugger framework
- faulthandler — Dump the Python traceback
- pdb — The Python Debugger
- The Python Profilers
- timeit — 測量小代碼片段的執行時間
- trace — Trace or track Python statement execution
- tracemalloc — Trace memory allocations
- 軟件打包和分發
- distutils — 構建和安裝 Python 模塊
- ensurepip — Bootstrapping the pip installer
- venv — 創建虛擬環境
- zipapp — Manage executable Python zip archives
- Python運行時服務
- sys — 系統相關的參數和函數
- sysconfig — Provide access to Python's configuration information
- builtins — 內建對象
- main — 頂層腳本環境
- warnings — Warning control
- dataclasses — 數據類
- contextlib — Utilities for with-statement contexts
- abc — 抽象基類
- atexit — 退出處理器
- traceback — Print or retrieve a stack traceback
- future — Future 語句定義
- gc — 垃圾回收器接口
- inspect — 檢查對象
- site — Site-specific configuration hook
- 自定義 Python 解釋器
- code — Interpreter base classes
- codeop — Compile Python code
- 導入模塊
- zipimport — Import modules from Zip archives
- pkgutil — Package extension utility
- modulefinder — 查找腳本使用的模塊
- runpy — Locating and executing Python modules
- importlib — The implementation of import
- Python 語言服務
- parser — Access Python parse trees
- ast — 抽象語法樹
- symtable — Access to the compiler's symbol tables
- symbol — 與 Python 解析樹一起使用的常量
- token — 與Python解析樹一起使用的常量
- keyword — 檢驗Python關鍵字
- tokenize — Tokenizer for Python source
- tabnanny — 模糊縮進檢測
- pyclbr — Python class browser support
- py_compile — Compile Python source files
- compileall — Byte-compile Python libraries
- dis — Python 字節碼反匯編器
- pickletools — Tools for pickle developers
- 雜項服務
- formatter — Generic output formatting
- Windows系統相關模塊
- msilib — Read and write Microsoft Installer files
- msvcrt — Useful routines from the MS VC++ runtime
- winreg — Windows 注冊表訪問
- winsound — Sound-playing interface for Windows
- Unix 專有服務
- posix — The most common POSIX system calls
- pwd — 用戶密碼數據庫
- spwd — The shadow password database
- grp — The group database
- crypt — Function to check Unix passwords
- termios — POSIX style tty control
- tty — 終端控制功能
- pty — Pseudo-terminal utilities
- fcntl — The fcntl and ioctl system calls
- pipes — Interface to shell pipelines
- resource — Resource usage information
- nis — Interface to Sun's NIS (Yellow Pages)
- Unix syslog 庫例程
- 被取代的模塊
- optparse — Parser for command line options
- imp — Access the import internals
- 未創建文檔的模塊
- 平臺特定模塊
- 擴展和嵌入 Python 解釋器
- 推薦的第三方工具
- 不使用第三方工具創建擴展
- 使用 C 或 C++ 擴展 Python
- 自定義擴展類型:教程
- 定義擴展類型:已分類主題
- 構建C/C++擴展
- 在Windows平臺編譯C和C++擴展
- 在更大的應用程序中嵌入 CPython 運行時
- Embedding Python in Another Application
- Python/C API 參考手冊
- 概述
- 代碼標準
- 包含文件
- 有用的宏
- 對象、類型和引用計數
- 異常
- 嵌入Python
- 調試構建
- 穩定的應用程序二進制接口
- The Very High Level Layer
- Reference Counting
- 異常處理
- Printing and clearing
- 拋出異常
- Issuing warnings
- Querying the error indicator
- Signal Handling
- Exception Classes
- Exception Objects
- Unicode Exception Objects
- Recursion Control
- 標準異常
- 標準警告類別
- 工具
- 操作系統實用程序
- 系統功能
- 過程控制
- 導入模塊
- Data marshalling support
- 語句解釋及變量編譯
- 字符串轉換與格式化
- 反射
- 編解碼器注冊與支持功能
- 抽象對象層
- Object Protocol
- 數字協議
- Sequence Protocol
- Mapping Protocol
- 迭代器協議
- 緩沖協議
- Old Buffer Protocol
- 具體的對象層
- 基本對象
- 數值對象
- 序列對象
- 容器對象
- 函數對象
- 其他對象
- Initialization, Finalization, and Threads
- 在Python初始化之前
- 全局配置變量
- Initializing and finalizing the interpreter
- Process-wide parameters
- Thread State and the Global Interpreter Lock
- Sub-interpreter support
- Asynchronous Notifications
- Profiling and Tracing
- Advanced Debugger Support
- Thread Local Storage Support
- 內存管理
- 概述
- 原始內存接口
- Memory Interface
- 對象分配器
- 默認內存分配器
- Customize Memory Allocators
- The pymalloc allocator
- tracemalloc C API
- 示例
- 對象實現支持
- 在堆中分配對象
- Common Object Structures
- Type 對象
- Number Object Structures
- Mapping Object Structures
- Sequence Object Structures
- Buffer Object Structures
- Async Object Structures
- 使對象類型支持循環垃圾回收
- API 和 ABI 版本管理
- 分發 Python 模塊
- 關鍵術語
- 開源許可與協作
- 安裝工具
- 閱讀指南
- 我該如何...?
- ...為我的項目選擇一個名字?
- ...創建和分發二進制擴展?
- 安裝 Python 模塊
- 關鍵術語
- 基本使用
- 我應如何 ...?
- ... 在 Python 3.4 之前的 Python 版本中安裝 pip ?
- ... 只為當前用戶安裝軟件包?
- ... 安裝科學計算類 Python 軟件包?
- ... 使用并行安裝的多個 Python 版本?
- 常見的安裝問題
- 在 Linux 的系統 Python 版本上安裝
- 未安裝 pip
- 安裝二進制編譯擴展
- Python 常用指引
- 將 Python 2 代碼遷移到 Python 3
- 簡要說明
- 詳情
- 將擴展模塊移植到 Python 3
- 條件編譯
- 對象API的更改
- 模塊初始化和狀態
- CObject 替換為 Capsule
- 其他選項
- Curses Programming with Python
- What is curses?
- Starting and ending a curses application
- Windows and Pads
- Displaying Text
- User Input
- For More Information
- 實現描述器
- 摘要
- 定義和簡介
- 描述器協議
- 發起調用描述符
- 描述符示例
- Properties
- 函數和方法
- Static Methods and Class Methods
- 函數式編程指引
- 概述
- 迭代器
- 生成器表達式和列表推導式
- 生成器
- 內置函數
- itertools 模塊
- The functools module
- Small functions and the lambda expression
- Revision History and Acknowledgements
- 引用文獻
- 日志 HOWTO
- 日志基礎教程
- 進階日志教程
- 日志級別
- 有用的處理程序
- 記錄日志中引發的異常
- 使用任意對象作為消息
- 優化
- 日志操作手冊
- 在多個模塊中使用日志
- 在多線程中使用日志
- 使用多個日志處理器和多種格式化
- 在多個地方記錄日志
- 日志服務器配置示例
- 處理日志處理器的阻塞
- Sending and receiving logging events across a network
- Adding contextual information to your logging output
- Logging to a single file from multiple processes
- Using file rotation
- Use of alternative formatting styles
- Customizing LogRecord
- Subclassing QueueHandler - a ZeroMQ example
- Subclassing QueueListener - a ZeroMQ example
- An example dictionary-based configuration
- Using a rotator and namer to customize log rotation processing
- A more elaborate multiprocessing example
- Inserting a BOM into messages sent to a SysLogHandler
- Implementing structured logging
- Customizing handlers with dictConfig()
- Using particular formatting styles throughout your application
- Configuring filters with dictConfig()
- Customized exception formatting
- Speaking logging messages
- Buffering logging messages and outputting them conditionally
- Formatting times using UTC (GMT) via configuration
- Using a context manager for selective logging
- 正則表達式HOWTO
- 概述
- 簡單模式
- 使用正則表達式
- 更多模式能力
- 修改字符串
- 常見問題
- 反饋
- 套接字編程指南
- 套接字
- 創建套接字
- 使用一個套接字
- 斷開連接
- 非阻塞的套接字
- 排序指南
- 基本排序
- 關鍵函數
- Operator 模塊函數
- 升序和降序
- 排序穩定性和排序復雜度
- 使用裝飾-排序-去裝飾的舊方法
- 使用 cmp 參數的舊方法
- 其它
- Unicode 指南
- Unicode 概述
- Python's Unicode Support
- Reading and Writing Unicode Data
- Acknowledgements
- 如何使用urllib包獲取網絡資源
- 概述
- Fetching URLs
- 處理異常
- info and geturl
- Openers and Handlers
- Basic Authentication
- Proxies
- Sockets and Layers
- 腳注
- Argparse 教程
- 概念
- 基礎
- 位置參數介紹
- Introducing Optional arguments
- Combining Positional and Optional arguments
- Getting a little more advanced
- Conclusion
- ipaddress模塊介紹
- 創建 Address/Network/Interface 對象
- 審查 Address/Network/Interface 對象
- Network 作為 Address 列表
- 比較
- 將IP地址與其他模塊一起使用
- 實例創建失敗時獲取更多詳細信息
- Argument Clinic How-To
- The Goals Of Argument Clinic
- Basic Concepts And Usage
- Converting Your First Function
- Advanced Topics
- 使用 DTrace 和 SystemTap 檢測CPython
- Enabling the static markers
- Static DTrace probes
- Static SystemTap markers
- Available static markers
- SystemTap Tapsets
- 示例
- Python 常見問題
- Python常見問題
- 一般信息
- 現實世界中的 Python
- 編程常見問題
- 一般問題
- 核心語言
- 數字和字符串
- 性能
- 序列(元組/列表)
- 對象
- 模塊
- 設計和歷史常見問題
- 為什么Python使用縮進來分組語句?
- 為什么簡單的算術運算得到奇怪的結果?
- 為什么浮點計算不準確?
- 為什么Python字符串是不可變的?
- 為什么必須在方法定義和調用中顯式使用“self”?
- 為什么不能在表達式中賦值?
- 為什么Python對某些功能(例如list.index())使用方法來實現,而其他功能(例如len(List))使用函數實現?
- 為什么 join()是一個字符串方法而不是列表或元組方法?
- 異常有多快?
- 為什么Python中沒有switch或case語句?
- 難道不能在解釋器中模擬線程,而非得依賴特定于操作系統的線程實現嗎?
- 為什么lambda表達式不能包含語句?
- 可以將Python編譯為機器代碼,C或其他語言嗎?
- Python如何管理內存?
- 為什么CPython不使用更傳統的垃圾回收方案?
- CPython退出時為什么不釋放所有內存?
- 為什么有單獨的元組和列表數據類型?
- 列表是如何在CPython中實現的?
- 字典是如何在CPython中實現的?
- 為什么字典key必須是不可變的?
- 為什么 list.sort() 沒有返回排序列表?
- 如何在Python中指定和實施接口規范?
- 為什么沒有goto?
- 為什么原始字符串(r-strings)不能以反斜杠結尾?
- 為什么Python沒有屬性賦值的“with”語句?
- 為什么 if/while/def/class語句需要冒號?
- 為什么Python在列表和元組的末尾允許使用逗號?
- 代碼庫和插件 FAQ
- 通用的代碼庫問題
- 通用任務
- 線程相關
- 輸入輸出
- 網絡 / Internet 編程
- 數據庫
- 數學和數字
- 擴展/嵌入常見問題
- 可以使用C語言中創建自己的函數嗎?
- 可以使用C++語言中創建自己的函數嗎?
- C很難寫,有沒有其他選擇?
- 如何從C執行任意Python語句?
- 如何從C中評估任意Python表達式?
- 如何從Python對象中提取C的值?
- 如何使用Py_BuildValue()創建任意長度的元組?
- 如何從C調用對象的方法?
- 如何捕獲PyErr_Print()(或打印到stdout / stderr的任何內容)的輸出?
- 如何從C訪問用Python編寫的模塊?
- 如何從Python接口到C ++對象?
- 我使用Setup文件添加了一個模塊,為什么make失敗了?
- 如何調試擴展?
- 我想在Linux系統上編譯一個Python模塊,但是缺少一些文件。為什么?
- 如何區分“輸入不完整”和“輸入無效”?
- 如何找到未定義的g++符號__builtin_new或__pure_virtual?
- 能否創建一個對象類,其中部分方法在C中實現,而其他方法在Python中實現(例如通過繼承)?
- Python在Windows上的常見問題
- 我怎樣在Windows下運行一個Python程序?
- 我怎么讓 Python 腳本可執行?
- 為什么有時候 Python 程序會啟動緩慢?
- 我怎樣使用Python腳本制作可執行文件?
- *.pyd 文件和DLL文件相同嗎?
- 我怎樣將Python嵌入一個Windows程序?
- 如何讓編輯器不要在我的 Python 源代碼中插入 tab ?
- 如何在不阻塞的情況下檢查按鍵?
- 圖形用戶界面(GUI)常見問題
- 圖形界面常見問題
- Python 是否有平臺無關的圖形界面工具包?
- 有哪些Python的GUI工具是某個平臺專用的?
- 有關Tkinter的問題
- “為什么我的電腦上安裝了 Python ?”
- 什么是Python?
- 為什么我的電腦上安裝了 Python ?
- 我能刪除 Python 嗎?
- 術語對照表
- 文檔說明
- Python 文檔貢獻者
- 解決 Bug
- 文檔錯誤
- 使用 Python 的錯誤追蹤系統
- 開始為 Python 貢獻您的知識
- 版權
- 歷史和許可證
- 軟件歷史
- 訪問Python或以其他方式使用Python的條款和條件
- Python 3.7.3 的 PSF 許可協議
- Python 2.0 的 BeOpen.com 許可協議
- Python 1.6.1 的 CNRI 許可協議
- Python 0.9.0 至 1.2 的 CWI 許可協議
- 集成軟件的許可和認可
- Mersenne Twister
- 套接字
- Asynchronous socket services
- Cookie management
- Execution tracing
- UUencode and UUdecode functions
- XML Remote Procedure Calls
- test_epoll
- Select kqueue
- SipHash24
- strtod and dtoa
- OpenSSL
- expat
- libffi
- zlib
- cfuhash
- libmpdec