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# What's New in Python 2.4
作者A.M. Kuchling
This article explains the new features in Python 2.4.1, released on March 30, 2005.
Python 2.4 is a medium-sized release. It doesn't introduce as many changes as the radical Python 2.2, but introduces more features than the conservative 2.3 release. The most significant new language features are function decorators and generator expressions; most other changes are to the standard library.
According to the CVS change logs, there were 481 patches applied and 502 bugs fixed between Python 2.3 and 2.4. Both figures are likely to be underestimates.
This article doesn't attempt to provide a complete specification of every single new feature, but instead provides a brief introduction to each feature. For full details, you should refer to the documentation for Python 2.4, such as the Python Library Reference and the Python Reference Manual. Often you will be referred to the PEP for a particular new feature for explanations of the implementation and design rationale.
## PEP 218: Built-In Set Objects
Python 2.3 introduced the `sets` module. C implementations of set data types have now been added to the Python core as two new built-in types, `set(iterable)` and `frozenset(iterable)`. They provide high speed operations for membership testing, for eliminating duplicates from sequences, and for mathematical operations like unions, intersections, differences, and symmetric differences.
```
>>> a = set('abracadabra') # form a set from a string
>>> 'z' in a # fast membership testing
False
>>> a # unique letters in a
set(['a', 'r', 'b', 'c', 'd'])
>>> ''.join(a) # convert back into a string
'arbcd'
>>> b = set('alacazam') # form a second set
>>> a - b # letters in a but not in b
set(['r', 'd', 'b'])
>>> a | b # letters in either a or b
set(['a', 'c', 'r', 'd', 'b', 'm', 'z', 'l'])
>>> a & b # letters in both a and b
set(['a', 'c'])
>>> a ^ b # letters in a or b but not both
set(['r', 'd', 'b', 'm', 'z', 'l'])
>>> a.add('z') # add a new element
>>> a.update('wxy') # add multiple new elements
>>> a
set(['a', 'c', 'b', 'd', 'r', 'w', 'y', 'x', 'z'])
>>> a.remove('x') # take one element out
>>> a
set(['a', 'c', 'b', 'd', 'r', 'w', 'y', 'z'])
```
The [`frozenset()`](../library/stdtypes.xhtml#frozenset "frozenset") type is an immutable version of [`set()`](../library/stdtypes.xhtml#set "set"). Since it is immutable and hashable, it may be used as a dictionary key or as a member of another set.
The `sets` module remains in the standard library, and may be useful if you wish to subclass the `Set` or `ImmutableSet` classes. There are currently no plans to deprecate the module.
參見
[**PEP 218**](https://www.python.org/dev/peps/pep-0218) \[https://www.python.org/dev/peps/pep-0218\] - Adding a Built-In Set Object TypeOriginally proposed by Greg Wilson and ultimately implemented by Raymond Hettinger.
## PEP 237: Unifying Long Integers and Integers
The lengthy transition process for this PEP, begun in Python 2.2, takes another step forward in Python 2.4. In 2.3, certain integer operations that would behave differently after int/long unification triggered [`FutureWarning`](../library/exceptions.xhtml#FutureWarning "FutureWarning")warnings and returned values limited to 32 or 64 bits (depending on your platform). In 2.4, these expressions no longer produce a warning and instead produce a different result that's usually a long integer.
The problematic expressions are primarily left shifts and lengthy hexadecimal and octal constants. For example, `2 << 32` results in a warning in 2.3, evaluating to 0 on 32-bit platforms. In Python 2.4, this expression now returns the correct answer, 8589934592.
參見
[**PEP 237**](https://www.python.org/dev/peps/pep-0237) \[https://www.python.org/dev/peps/pep-0237\] - Unifying Long Integers and IntegersOriginal PEP written by Moshe Zadka and GvR. The changes for 2.4 were implemented by Kalle Svensson.
## PEP 289: Generator Expressions
The iterator feature introduced in Python 2.2 and the [`itertools`](../library/itertools.xhtml#module-itertools "itertools: Functions creating iterators for efficient looping.") module make it easier to write programs that loop through large data sets without having the entire data set in memory at one time. List comprehensions don't fit into this picture very well because they produce a Python list object containing all of the items. This unavoidably pulls all of the objects into memory, which can be a problem if your data set is very large. When trying to write a functionally-styled program, it would be natural to write something like:
```
links = [link for link in get_all_links() if not link.followed]
for link in links:
...
```
instead of
```
for link in get_all_links():
if link.followed:
continue
...
```
The first form is more concise and perhaps more readable, but if you're dealing with a large number of link objects you'd have to write the second form to avoid having all link objects in memory at the same time.
Generator expressions work similarly to list comprehensions but don't materialize the entire list; instead they create a generator that will return elements one by one. The above example could be written as:
```
links = (link for link in get_all_links() if not link.followed)
for link in links:
...
```
Generator expressions always have to be written inside parentheses, as in the above example. The parentheses signalling a function call also count, so if you want to create an iterator that will be immediately passed to a function you could write:
```
print sum(obj.count for obj in list_all_objects())
```
Generator expressions differ from list comprehensions in various small ways. Most notably, the loop variable (*obj* in the above example) is not accessible outside of the generator expression. List comprehensions leave the variable assigned to its last value; future versions of Python will change this, making list comprehensions match generator expressions in this respect.
參見
[**PEP 289**](https://www.python.org/dev/peps/pep-0289) \[https://www.python.org/dev/peps/pep-0289\] - Generator ExpressionsProposed by Raymond Hettinger and implemented by Jiwon Seo with early efforts steered by Hye-Shik Chang.
## PEP 292: Simpler String Substitutions
Some new classes in the standard library provide an alternative mechanism for substituting variables into strings; this style of substitution may be better for applications where untrained users need to edit templates.
The usual way of substituting variables by name is the `%` operator:
```
>>> '%(page)i: %(title)s' % {'page':2, 'title': 'The Best of Times'}
'2: The Best of Times'
```
When writing the template string, it can be easy to forget the `i` or `s`after the closing parenthesis. This isn't a big problem if the template is in a Python module, because you run the code, get an "Unsupported format character" [`ValueError`](../library/exceptions.xhtml#ValueError "ValueError"), and fix the problem. However, consider an application such as Mailman where template strings or translations are being edited by users who aren't aware of the Python language. The format string's syntax is complicated to explain to such users, and if they make a mistake, it's difficult to provide helpful feedback to them.
PEP 292 adds a `Template` class to the [`string`](../library/string.xhtml#module-string "string: Common string operations.") module that uses `$` to indicate a substitution:
```
>>> import string
>>> t = string.Template('$page: $title')
>>> t.substitute({'page':2, 'title': 'The Best of Times'})
'2: The Best of Times'
```
If a key is missing from the dictionary, the `substitute()` method will raise a [`KeyError`](../library/exceptions.xhtml#KeyError "KeyError"). There's also a `safe_substitute()` method that ignores missing keys:
```
>>> t = string.Template('$page: $title')
>>> t.safe_substitute({'page':3})
'3: $title'
```
參見
[**PEP 292**](https://www.python.org/dev/peps/pep-0292) \[https://www.python.org/dev/peps/pep-0292\] - Simpler String SubstitutionsWritten and implemented by Barry Warsaw.
## PEP 318: Decorators for Functions and Methods
Python 2.2 extended Python's object model by adding static methods and class methods, but it didn't extend Python's syntax to provide any new way of defining static or class methods. Instead, you had to write a [`def`](../reference/compound_stmts.xhtml#def) statement in the usual way, and pass the resulting method to a [`staticmethod()`](../library/functions.xhtml#staticmethod "staticmethod") or [`classmethod()`](../library/functions.xhtml#classmethod "classmethod") function that would wrap up the function as a method of the new type. Your code would look like this:
```
class C:
def meth (cls):
...
meth = classmethod(meth) # Rebind name to wrapped-up class method
```
If the method was very long, it would be easy to miss or forget the [`classmethod()`](../library/functions.xhtml#classmethod "classmethod") invocation after the function body.
The intention was always to add some syntax to make such definitions more readable, but at the time of 2.2's release a good syntax was not obvious. Today a good syntax *still* isn't obvious but users are asking for easier access to the feature; a new syntactic feature has been added to meet this need.
The new feature is called "function decorators". The name comes from the idea that [`classmethod()`](../library/functions.xhtml#classmethod "classmethod"), [`staticmethod()`](../library/functions.xhtml#staticmethod "staticmethod"), and friends are storing additional information on a function object; they're *decorating* functions with more details.
The notation borrows from Java and uses the `'@'` character as an indicator. Using the new syntax, the example above would be written:
```
class C:
@classmethod
def meth (cls):
...
```
The `@classmethod` is shorthand for the `meth=classmethod(meth)` assignment. More generally, if you have the following:
```
@A
@B
@C
def f ():
...
```
It's equivalent to the following pre-decorator code:
```
def f(): ...
f = A(B(C(f)))
```
Decorators must come on the line before a function definition, one decorator per line, and can't be on the same line as the def statement, meaning that
```
@A def
f(): ...
```
is illegal. You can only decorate function definitions, either at the module level or inside a class; you can't decorate class definitions.
A decorator is just a function that takes the function to be decorated as an argument and returns either the same function or some new object. The return value of the decorator need not be callable (though it typically is), unless further decorators will be applied to the result. It's easy to write your own decorators. The following simple example just sets an attribute on the function object:
```
>>> def deco(func):
... func.attr = 'decorated'
... return func
...
>>> @deco
... def f(): pass
...
>>> f
<function f at 0x402ef0d4>
>>> f.attr
'decorated'
>>>
```
As a slightly more realistic example, the following decorator checks that the supplied argument is an integer:
```
def require_int (func):
def wrapper (arg):
assert isinstance(arg, int)
return func(arg)
return wrapper
@require_int
def p1 (arg):
print arg
@require_int
def p2(arg):
print arg*2
```
An example in [**PEP 318**](https://www.python.org/dev/peps/pep-0318) \[https://www.python.org/dev/peps/pep-0318\] contains a fancier version of this idea that lets you both specify the required type and check the returned type.
Decorator functions can take arguments. If arguments are supplied, your decorator function is called with only those arguments and must return a new decorator function; this function must take a single function and return a function, as previously described. In other words, `@A @B @C(args)` becomes:
```
def f(): ...
_deco = C(args)
f = A(B(_deco(f)))
```
Getting this right can be slightly brain-bending, but it's not too difficult.
A small related change makes the `func_name` attribute of functions writable. This attribute is used to display function names in tracebacks, so decorators should change the name of any new function that's constructed and returned.
參見
[**PEP 318**](https://www.python.org/dev/peps/pep-0318) \[https://www.python.org/dev/peps/pep-0318\] - Decorators for Functions, Methods and ClassesWritten by Kevin D. Smith, Jim Jewett, and Skip Montanaro. Several people wrote patches implementing function decorators, but the one that was actually checked in was patch #979728, written by Mark Russell.
<https://wiki.python.org/moin/PythonDecoratorLibrary>This Wiki page contains several examples of decorators.
## PEP 322: Reverse Iteration
A new built-in function, `reversed(seq)`, takes a sequence and returns an iterator that loops over the elements of the sequence in reverse order.
```
>>> for i in reversed(xrange(1,4)):
... print i
...
3
2
1
```
Compared to extended slicing, such as `range(1,4)[::-1]`, [`reversed()`](../library/functions.xhtml#reversed "reversed") is easier to read, runs faster, and uses substantially less memory.
Note that [`reversed()`](../library/functions.xhtml#reversed "reversed") only accepts sequences, not arbitrary iterators. If you want to reverse an iterator, first convert it to a list with [`list()`](../library/stdtypes.xhtml#list "list").
```
>>> input = open('/etc/passwd', 'r')
>>> for line in reversed(list(input)):
... print line
...
root:*:0:0:System Administrator:/var/root:/bin/tcsh
...
```
參見
[**PEP 322**](https://www.python.org/dev/peps/pep-0322) \[https://www.python.org/dev/peps/pep-0322\] - Reverse IterationWritten and implemented by Raymond Hettinger.
## PEP 324: New subprocess Module
The standard library provides a number of ways to execute a subprocess, offering different features and different levels of complexity. `os.system(command)` is easy to use, but slow (it runs a shell process which executes the command) and dangerous (you have to be careful about escaping the shell's metacharacters). The `popen2` module offers classes that can capture standard output and standard error from the subprocess, but the naming is confusing. The [`subprocess`](../library/subprocess.xhtml#module-subprocess "subprocess: Subprocess management.") module cleans this up, providing a unified interface that offers all the features you might need.
Instead of `popen2`'s collection of classes, [`subprocess`](../library/subprocess.xhtml#module-subprocess "subprocess: Subprocess management.") contains a single class called `Popen` whose constructor supports a number of different keyword arguments.
```
class Popen(args, bufsize=0, executable=None,
stdin=None, stdout=None, stderr=None,
preexec_fn=None, close_fds=False, shell=False,
cwd=None, env=None, universal_newlines=False,
startupinfo=None, creationflags=0):
```
*args* is commonly a sequence of strings that will be the arguments to the program executed as the subprocess. (If the *shell* argument is true, *args*can be a string which will then be passed on to the shell for interpretation, just as [`os.system()`](../library/os.xhtml#os.system "os.system") does.)
*stdin*, *stdout*, and *stderr* specify what the subprocess's input, output, and error streams will be. You can provide a file object or a file descriptor, or you can use the constant `subprocess.PIPE` to create a pipe between the subprocess and the parent.
The constructor has a number of handy options:
- *close\_fds* requests that all file descriptors be closed before running the subprocess.
- *cwd* specifies the working directory in which the subprocess will be executed (defaulting to whatever the parent's working directory is).
- *env* is a dictionary specifying environment variables.
- *preexec\_fn* is a function that gets called before the child is started.
- *universal\_newlines* opens the child's input and output using Python's [universal newlines](../glossary.xhtml#term-universal-newlines) feature.
Once you've created the `Popen` instance, you can call its `wait()`method to pause until the subprocess has exited, `poll()` to check if it's exited without pausing, or `communicate(data)` to send the string *data*to the subprocess's standard input. `communicate(data)` then reads any data that the subprocess has sent to its standard output or standard error, returning a tuple `(stdout_data, stderr_data)`.
`call()` is a shortcut that passes its arguments along to the `Popen`constructor, waits for the command to complete, and returns the status code of the subprocess. It can serve as a safer analog to [`os.system()`](../library/os.xhtml#os.system "os.system"):
```
sts = subprocess.call(['dpkg', '-i', '/tmp/new-package.deb'])
if sts == 0:
# Success
...
else:
# dpkg returned an error
...
```
The command is invoked without use of the shell. If you really do want to use the shell, you can add `shell=True` as a keyword argument and provide a string instead of a sequence:
```
sts = subprocess.call('dpkg -i /tmp/new-package.deb', shell=True)
```
The PEP takes various examples of shell and Python code and shows how they'd be translated into Python code that uses [`subprocess`](../library/subprocess.xhtml#module-subprocess "subprocess: Subprocess management."). Reading this section of the PEP is highly recommended.
參見
[**PEP 324**](https://www.python.org/dev/peps/pep-0324) \[https://www.python.org/dev/peps/pep-0324\] - subprocess - New process moduleWritten and implemented by Peter ?strand, with assistance from Fredrik Lundh and others.
## PEP 327: Decimal Data Type
Python has always supported floating-point (FP) numbers, based on the underlying C `double` type, as a data type. However, while most programming languages provide a floating-point type, many people (even programmers) are unaware that floating-point numbers don't represent certain decimal fractions accurately. The new `Decimal` type can represent these fractions accurately, up to a user-specified precision limit.
### Why is Decimal needed?
The limitations arise from the representation used for floating-point numbers. FP numbers are made up of three components:
- The sign, which is positive or negative.
- The mantissa, which is a single-digit binary number followed by a fractional part. For example, `1.01` in base-2 notation is `1 + 0/2 + 1/4`, or 1.25 in decimal notation.
- The exponent, which tells where the decimal point is located in the number represented.
For example, the number 1.25 has positive sign, a mantissa value of 1.01 (in binary), and an exponent of 0 (the decimal point doesn't need to be shifted). The number 5 has the same sign and mantissa, but the exponent is 2 because the mantissa is multiplied by 4 (2 to the power of the exponent 2); 1.25 \* 4 equals 5.
Modern systems usually provide floating-point support that conforms to a standard called IEEE 754. C's `double` type is usually implemented as a 64-bit IEEE 754 number, which uses 52 bits of space for the mantissa. This means that numbers can only be specified to 52 bits of precision. If you're trying to represent numbers whose expansion repeats endlessly, the expansion is cut off after 52 bits. Unfortunately, most software needs to produce output in base 10, and common fractions in base 10 are often repeating decimals in binary. For example, 1.1 decimal is binary `1.0001100110011 ...`; .1 = 1/16 + 1/32 + 1/256 plus an infinite number of additional terms. IEEE 754 has to chop off that infinitely repeated decimal after 52 digits, so the representation is slightly inaccurate.
Sometimes you can see this inaccuracy when the number is printed:
```
>>> 1.1
1.1000000000000001
```
The inaccuracy isn't always visible when you print the number because the FP-to-decimal-string conversion is provided by the C library, and most C libraries try to produce sensible output. Even if it's not displayed, however, the inaccuracy is still there and subsequent operations can magnify the error.
For many applications this doesn't matter. If I'm plotting points and displaying them on my monitor, the difference between 1.1 and 1.1000000000000001 is too small to be visible. Reports often limit output to a certain number of decimal places, and if you round the number to two or three or even eight decimal places, the error is never apparent. However, for applications where it does matter, it's a lot of work to implement your own custom arithmetic routines.
Hence, the `Decimal` type was created.
### The `Decimal` type
A new module, [`decimal`](../library/decimal.xhtml#module-decimal "decimal: Implementation of the General Decimal Arithmetic Specification."), was added to Python's standard library. It contains two classes, `Decimal` and `Context`. `Decimal`instances represent numbers, and `Context` instances are used to wrap up various settings such as the precision and default rounding mode.
`Decimal` instances are immutable, like regular Python integers and FP numbers; once it's been created, you can't change the value an instance represents. `Decimal` instances can be created from integers or strings:
```
>>> import decimal
>>> decimal.Decimal(1972)
Decimal("1972")
>>> decimal.Decimal("1.1")
Decimal("1.1")
```
You can also provide tuples containing the sign, the mantissa represented as a tuple of decimal digits, and the exponent:
```
>>> decimal.Decimal((1, (1, 4, 7, 5), -2))
Decimal("-14.75")
```
Cautionary note: the sign bit is a Boolean value, so 0 is positive and 1 is negative.
Converting from floating-point numbers poses a bit of a problem: should the FP number representing 1.1 turn into the decimal number for exactly 1.1, or for 1.1 plus whatever inaccuracies are introduced? The decision was to dodge the issue and leave such a conversion out of the API. Instead, you should convert the floating-point number into a string using the desired precision and pass the string to the `Decimal` constructor:
```
>>> f = 1.1
>>> decimal.Decimal(str(f))
Decimal("1.1")
>>> decimal.Decimal('%.12f' % f)
Decimal("1.100000000000")
```
Once you have `Decimal` instances, you can perform the usual mathematical operations on them. One limitation: exponentiation requires an integer exponent:
```
>>> a = decimal.Decimal('35.72')
>>> b = decimal.Decimal('1.73')
>>> a+b
Decimal("37.45")
>>> a-b
Decimal("33.99")
>>> a*b
Decimal("61.7956")
>>> a/b
Decimal("20.64739884393063583815028902")
>>> a ** 2
Decimal("1275.9184")
>>> a**b
Traceback (most recent call last):
...
decimal.InvalidOperation: x ** (non-integer)
```
You can combine `Decimal` instances with integers, but not with floating-point numbers:
```
>>> a + 4
Decimal("39.72")
>>> a + 4.5
Traceback (most recent call last):
...
TypeError: You can interact Decimal only with int, long or Decimal data types.
>>>
```
`Decimal` numbers can be used with the [`math`](../library/math.xhtml#module-math "math: Mathematical functions (sin() etc.).") and [`cmath`](../library/cmath.xhtml#module-cmath "cmath: Mathematical functions for complex numbers.")modules, but note that they'll be immediately converted to floating-point numbers before the operation is performed, resulting in a possible loss of precision and accuracy. You'll also get back a regular floating-point number and not a `Decimal`.
```
>>> import math, cmath
>>> d = decimal.Decimal('123456789012.345')
>>> math.sqrt(d)
351364.18288201344
>>> cmath.sqrt(-d)
351364.18288201344j
```
`Decimal` instances have a `sqrt()` method that returns a `Decimal`, but if you need other things such as trigonometric functions you'll have to implement them.
```
>>> d.sqrt()
Decimal("351364.1828820134592177245001")
```
### The `Context` type
Instances of the `Context` class encapsulate several settings for decimal operations:
- `prec` is the precision, the number of decimal places.
- `rounding` specifies the rounding mode. The [`decimal`](../library/decimal.xhtml#module-decimal "decimal: Implementation of the General Decimal Arithmetic Specification.") module has constants for the various possibilities: `ROUND_DOWN`, `ROUND_CEILING`, `ROUND_HALF_EVEN`, and various others.
- `traps` is a dictionary specifying what happens on encountering certain error conditions: either an exception is raised or a value is returned. Some examples of error conditions are division by zero, loss of precision, and overflow.
There's a thread-local default context available by calling `getcontext()`; you can change the properties of this context to alter the default precision, rounding, or trap handling. The following example shows the effect of changing the precision of the default context:
```
>>> decimal.getcontext().prec
28
>>> decimal.Decimal(1) / decimal.Decimal(7)
Decimal("0.1428571428571428571428571429")
>>> decimal.getcontext().prec = 9
>>> decimal.Decimal(1) / decimal.Decimal(7)
Decimal("0.142857143")
```
The default action for error conditions is selectable; the module can either return a special value such as infinity or not-a-number, or exceptions can be raised:
```
>>> decimal.Decimal(1) / decimal.Decimal(0)
Traceback (most recent call last):
...
decimal.DivisionByZero: x / 0
>>> decimal.getcontext().traps[decimal.DivisionByZero] = False
>>> decimal.Decimal(1) / decimal.Decimal(0)
Decimal("Infinity")
>>>
```
The `Context` instance also has various methods for formatting numbers such as `to_eng_string()` and `to_sci_string()`.
For more information, see the documentation for the [`decimal`](../library/decimal.xhtml#module-decimal "decimal: Implementation of the General Decimal Arithmetic Specification.") module, which includes a quick-start tutorial and a reference.
參見
[**PEP 327**](https://www.python.org/dev/peps/pep-0327) \[https://www.python.org/dev/peps/pep-0327\] - Decimal Data TypeWritten by Facundo Batista and implemented by Facundo Batista, Eric Price, Raymond Hettinger, Aahz, and Tim Peters.
<http://www.lahey.com/float.htm>The article uses Fortran code to illustrate many of the problems that floating-point inaccuracy can cause.
<http://speleotrove.com/decimal/>A description of a decimal-based representation. This representation is being proposed as a standard, and underlies the new Python decimal type. Much of this material was written by Mike Cowlishaw, designer of the Rexx language.
## PEP 328: Multi-line Imports
One language change is a small syntactic tweak aimed at making it easier to import many names from a module. In a `from module import names` statement, *names* is a sequence of names separated by commas. If the sequence is very long, you can either write multiple imports from the same module, or you can use backslashes to escape the line endings like this:
```
from SimpleXMLRPCServer import SimpleXMLRPCServer,\
SimpleXMLRPCRequestHandler,\
CGIXMLRPCRequestHandler,\
resolve_dotted_attribute
```
The syntactic change in Python 2.4 simply allows putting the names within parentheses. Python ignores newlines within a parenthesized expression, so the backslashes are no longer needed:
```
from SimpleXMLRPCServer import (SimpleXMLRPCServer,
SimpleXMLRPCRequestHandler,
CGIXMLRPCRequestHandler,
resolve_dotted_attribute)
```
The PEP also proposes that all [`import`](../reference/simple_stmts.xhtml#import) statements be absolute imports, with a leading `.` character to indicate a relative import. This part of the PEP was not implemented for Python 2.4, but was completed for Python 2.5.
參見
[**PEP 328**](https://www.python.org/dev/peps/pep-0328) \[https://www.python.org/dev/peps/pep-0328\] - Imports: Multi-Line and Absolute/RelativeWritten by Aahz. Multi-line imports were implemented by Dima Dorfman.
## PEP 331: Locale-Independent Float/String Conversions
The [`locale`](../library/locale.xhtml#module-locale "locale: Internationalization services.") modules lets Python software select various conversions and display conventions that are localized to a particular country or language. However, the module was careful to not change the numeric locale because various functions in Python's implementation required that the numeric locale remain set to the `'C'` locale. Often this was because the code was using the C library's `atof()` function.
Not setting the numeric locale caused trouble for extensions that used third-party C libraries, however, because they wouldn't have the correct locale set. The motivating example was GTK+, whose user interface widgets weren't displaying numbers in the current locale.
The solution described in the PEP is to add three new functions to the Python API that perform ASCII-only conversions, ignoring the locale setting:
- `PyOS_ascii_strtod(str, ptr)` and `PyOS_ascii_atof(str, ptr)`both convert a string to a C `double`.
- `PyOS_ascii_formatd(buffer, buf_len, format, d)` converts a `double` to an ASCII string.
The code for these functions came from the GLib library (<https://developer.gnome.org/glib/stable/>), whose developers kindly relicensed the relevant functions and donated them to the Python Software Foundation. The [`locale`](../library/locale.xhtml#module-locale "locale: Internationalization services.") module can now change the numeric locale, letting extensions such as GTK+ produce the correct results.
參見
[**PEP 331**](https://www.python.org/dev/peps/pep-0331) \[https://www.python.org/dev/peps/pep-0331\] - Locale-Independent Float/String ConversionsWritten by Christian R. Reis, and implemented by Gustavo Carneiro.
## 其他語言特性修改
Here are all of the changes that Python 2.4 makes to the core Python language.
- Decorators for functions and methods were added ([**PEP 318**](https://www.python.org/dev/peps/pep-0318) \[https://www.python.org/dev/peps/pep-0318\]).
- Built-in [`set()`](../library/stdtypes.xhtml#set "set") and [`frozenset()`](../library/stdtypes.xhtml#frozenset "frozenset") types were added ([**PEP 218**](https://www.python.org/dev/peps/pep-0218) \[https://www.python.org/dev/peps/pep-0218\]). Other new built-ins include the `reversed(seq)` function ([**PEP 322**](https://www.python.org/dev/peps/pep-0322) \[https://www.python.org/dev/peps/pep-0322\]).
- Generator expressions were added ([**PEP 289**](https://www.python.org/dev/peps/pep-0289) \[https://www.python.org/dev/peps/pep-0289\]).
- Certain numeric expressions no longer return values restricted to 32 or 64 bits ([**PEP 237**](https://www.python.org/dev/peps/pep-0237) \[https://www.python.org/dev/peps/pep-0237\]).
- You can now put parentheses around the list of names in a
```
from module import
names
```
statement ([**PEP 328**](https://www.python.org/dev/peps/pep-0328) \[https://www.python.org/dev/peps/pep-0328\]).
- The [`dict.update()`](../library/stdtypes.xhtml#dict.update "dict.update") method now accepts the same argument forms as the [`dict`](../library/stdtypes.xhtml#dict "dict") constructor. This includes any mapping, any iterable of key/value pairs, and keyword arguments. (Contributed by Raymond Hettinger.)
- The string methods `ljust()`, `rjust()`, and `center()` now take an optional argument for specifying a fill character other than a space. (Contributed by Raymond Hettinger.)
- Strings also gained an `rsplit()` method that works like the `split()`method but splits from the end of the string. (Contributed by Sean Reifschneider.)
```
>>> 'www.python.org'.split('.', 1)
['www', 'python.org']
'www.python.org'.rsplit('.', 1)
['www.python', 'org']
```
- Three keyword parameters, *cmp*, *key*, and *reverse*, were added to the `sort()` method of lists. These parameters make some common usages of `sort()` simpler. All of these parameters are optional.
For the *cmp* parameter, the value should be a comparison function that takes two parameters and returns -1, 0, or +1 depending on how the parameters compare. This function will then be used to sort the list. Previously this was the only parameter that could be provided to `sort()`.
*key* should be a single-parameter function that takes a list element and returns a comparison key for the element. The list is then sorted using the comparison keys. The following example sorts a list case-insensitively:
```
>>> L = ['A', 'b', 'c', 'D']
>>> L.sort() # Case-sensitive sort
>>> L
['A', 'D', 'b', 'c']
>>> # Using 'key' parameter to sort list
>>> L.sort(key=lambda x: x.lower())
>>> L
['A', 'b', 'c', 'D']
>>> # Old-fashioned way
>>> L.sort(cmp=lambda x,y: cmp(x.lower(), y.lower()))
>>> L
['A', 'b', 'c', 'D']
```
The last example, which uses the *cmp* parameter, is the old way to perform a case-insensitive sort. It works but is slower than using a *key* parameter. Using *key* calls `lower()` method once for each element in the list while using *cmp* will call it twice for each comparison, so using *key* saves on invocations of the `lower()` method.
For simple key functions and comparison functions, it is often possible to avoid a [`lambda`](../reference/expressions.xhtml#lambda) expression by using an unbound method instead. For example, the above case-insensitive sort is best written as:
```
>>> L.sort(key=str.lower)
>>> L
['A', 'b', 'c', 'D']
```
Finally, the *reverse* parameter takes a Boolean value. If the value is true, the list will be sorted into reverse order. Instead of
```
L.sort();
L.reverse()
```
, you can now write `L.sort(reverse=True)`.
The results of sorting are now guaranteed to be stable. This means that two entries with equal keys will be returned in the same order as they were input. For example, you can sort a list of people by name, and then sort the list by age, resulting in a list sorted by age where people with the same age are in name-sorted order.
(All changes to `sort()` contributed by Raymond Hettinger.)
- There is a new built-in function `sorted(iterable)` that works like the in-place [`list.sort()`](../library/stdtypes.xhtml#list.sort "list.sort") method but can be used in expressions. The differences are:
- the input may be any iterable;
- a newly formed copy is sorted, leaving the original intact; and
- the expression returns the new sorted copy
```
>>> L = [9,7,8,3,2,4,1,6,5]
>>> [10+i for i in sorted(L)] # usable in a list comprehension
[11, 12, 13, 14, 15, 16, 17, 18, 19]
>>> L # original is left unchanged
[9,7,8,3,2,4,1,6,5]
>>> sorted('Monty Python') # any iterable may be an input
[' ', 'M', 'P', 'h', 'n', 'n', 'o', 'o', 't', 't', 'y', 'y']
>>> # List the contents of a dict sorted by key values
>>> colormap = dict(red=1, blue=2, green=3, black=4, yellow=5)
>>> for k, v in sorted(colormap.iteritems()):
... print k, v
...
black 4
blue 2
green 3
red 1
yellow 5
```
(Contributed by Raymond Hettinger.)
- Integer operations will no longer trigger an `OverflowWarning`. The `OverflowWarning` warning will disappear in Python 2.5.
- The interpreter gained a new switch, [`-m`](../using/cmdline.xhtml#cmdoption-m), that takes a name, searches for the corresponding module on `sys.path`, and runs the module as a script. For example, you can now run the Python profiler with `python -m profile`. (Contributed by Nick Coghlan.)
- The `eval(expr, globals, locals)` and
```
execfile(filename, globals,
locals)
```
functions and the `exec` statement now accept any mapping type for the *locals* parameter. Previously this had to be a regular Python dictionary. (Contributed by Raymond Hettinger.)
- The [`zip()`](../library/functions.xhtml#zip "zip") built-in function and `itertools.izip()` now return an empty list if called with no arguments. Previously they raised a [`TypeError`](../library/exceptions.xhtml#TypeError "TypeError") exception. This makes them more suitable for use with variable length argument lists:
```
>>> def transpose(array):
... return zip(*array)
...
>>> transpose([(1,2,3), (4,5,6)])
[(1, 4), (2, 5), (3, 6)]
>>> transpose([])
[]
```
(Contributed by Raymond Hettinger.)
- Encountering a failure while importing a module no longer leaves a partially-initialized module object in `sys.modules`. The incomplete module object left behind would fool further imports of the same module into succeeding, leading to confusing errors. (Fixed by Tim Peters.)
- [`None`](../library/constants.xhtml#None "None") is now a constant; code that binds a new value to the name `None` is now a syntax error. (Contributed by Raymond Hettinger.)
### 性能優化
- The inner loops for list and tuple slicing were optimized and now run about one-third faster. The inner loops for dictionaries were also optimized, resulting in performance boosts for `keys()`, `values()`, `items()`, `iterkeys()`, `itervalues()`, and `iteritems()`. (Contributed by Raymond Hettinger.)
- The machinery for growing and shrinking lists was optimized for speed and for space efficiency. Appending and popping from lists now runs faster due to more efficient code paths and less frequent use of the underlying system `realloc()`. List comprehensions also benefit. `list.extend()` was also optimized and no longer converts its argument into a temporary list before extending the base list. (Contributed by Raymond Hettinger.)
- [`list()`](../library/stdtypes.xhtml#list "list"), [`tuple()`](../library/stdtypes.xhtml#tuple "tuple"), [`map()`](../library/functions.xhtml#map "map"), [`filter()`](../library/functions.xhtml#filter "filter"), and [`zip()`](../library/functions.xhtml#zip "zip") now run several times faster with non-sequence arguments that supply a [`__len__()`](../reference/datamodel.xhtml#object.__len__ "object.__len__") method. (Contributed by Raymond Hettinger.)
- The methods `list.__getitem__()`, `dict.__getitem__()`, and `dict.__contains__()` are now implemented as `method_descriptor`objects rather than `wrapper_descriptor` objects. This form of access doubles their performance and makes them more suitable for use as arguments to functionals: `map(mydict.__getitem__, keylist)`. (Contributed by Raymond Hettinger.)
- Added a new opcode, `LIST_APPEND`, that simplifies the generated bytecode for list comprehensions and speeds them up by about a third. (Contributed by Raymond Hettinger.)
- The peephole bytecode optimizer has been improved to produce shorter, faster bytecode; remarkably, the resulting bytecode is more readable. (Enhanced by Raymond Hettinger.)
- String concatenations in statements of the form `s = s + "abc"` and
```
s +=
"abc"
```
are now performed more efficiently in certain circumstances. This optimization won't be present in other Python implementations such as Jython, so you shouldn't rely on it; using the `join()` method of strings is still recommended when you want to efficiently glue a large number of strings together. (Contributed by Armin Rigo.)
The net result of the 2.4 optimizations is that Python 2.4 runs the pystone benchmark around 5% faster than Python 2.3 and 35% faster than Python 2.2. (pystone is not a particularly good benchmark, but it's the most commonly used measurement of Python's performance. Your own applications may show greater or smaller benefits from Python 2.4.)
## New, Improved, and Deprecated Modules
As usual, 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 CVS logs for all the details.
- The [`asyncore`](../library/asyncore.xhtml#module-asyncore "asyncore: A base class for developing asynchronous socket handling services.") module's `loop()` function now has a *count* parameter that lets you perform a limited number of passes through the polling loop. The default is still to loop forever.
- The [`base64`](../library/base64.xhtml#module-base64 "base64: RFC 3548: Base16, Base32, Base64 Data Encodings; Base85 and Ascii85") module now has more complete [**RFC 3548**](https://tools.ietf.org/html/rfc3548.html) \[https://tools.ietf.org/html/rfc3548.html\] support for Base64, Base32, and Base16 encoding and decoding, including optional case folding and optional alternative alphabets. (Contributed by Barry Warsaw.)
- The [`bisect`](../library/bisect.xhtml#module-bisect "bisect: Array bisection algorithms for binary searching.") module now has an underlying C implementation for improved performance. (Contributed by Dmitry Vasiliev.)
- The CJKCodecs collections of East Asian codecs, maintained by Hye-Shik Chang, was integrated into 2.4. The new encodings are:
- Chinese (PRC): gb2312, gbk, gb18030, big5hkscs, hz
- Chinese (ROC): big5, cp950
- Japanese: cp932, euc-jis-2004, euc-jp, euc-jisx0213, iso-2022-jp,iso-2022-jp-1, iso-2022-jp-2, iso-2022-jp-3, iso-2022-jp-ext, iso-2022-jp-2004, shift-jis, shift-jisx0213, shift-jis-2004
- Korean: cp949, euc-kr, johab, iso-2022-kr
- Some other new encodings were added: HP Roman8, ISO\_8859-11, ISO\_8859-16, PCTP-154, and TIS-620.
- The UTF-8 and UTF-16 codecs now cope better with receiving partial input. Previously the `StreamReader` class would try to read more data, making it impossible to resume decoding from the stream. The `read()` method will now return as much data as it can and future calls will resume decoding where previous ones left off. (Implemented by Walter D?rwald.)
- There is a new [`collections`](../library/collections.xhtml#module-collections "collections: Container datatypes") module for various specialized collection datatypes. Currently it contains just one type, `deque`, a double-ended queue that supports efficiently adding and removing elements from either end:
```
>>> from collections import deque
>>> d = deque('ghi') # make a new deque with three items
>>> d.append('j') # add a new entry to the right side
>>> d.appendleft('f') # add a new entry to the left side
>>> d # show the representation of the deque
deque(['f', 'g', 'h', 'i', 'j'])
>>> d.pop() # return and remove the rightmost item
'j'
>>> d.popleft() # return and remove the leftmost item
'f'
>>> list(d) # list the contents of the deque
['g', 'h', 'i']
>>> 'h' in d # search the deque
True
```
Several modules, such as the `Queue` and [`threading`](../library/threading.xhtml#module-threading "threading: Thread-based parallelism.") modules, now take advantage of [`collections.deque`](../library/collections.xhtml#collections.deque "collections.deque") for improved performance. (Contributed by Raymond Hettinger.)
- The `ConfigParser` classes have been enhanced slightly. The `read()`method now returns a list of the files that were successfully parsed, and the [`set()`](../library/stdtypes.xhtml#set "set") method raises [`TypeError`](../library/exceptions.xhtml#TypeError "TypeError") if passed a *value* argument that isn't a string. (Contributed by John Belmonte and David Goodger.)
- The [`curses`](../library/curses.xhtml#module-curses "curses: An interface to the curses library, providing portable terminal handling. (Unix)") module now supports the ncurses extension `use_default_colors()`. On platforms where the terminal supports transparency, this makes it possible to use a transparent background. (Contributed by J?rg Lehmann.)
- The [`difflib`](../library/difflib.xhtml#module-difflib "difflib: Helpers for computing differences between objects.") module now includes an `HtmlDiff` class that creates an HTML table showing a side by side comparison of two versions of a text. (Contributed by Dan Gass.)
- The [`email`](../library/email.xhtml#module-email "email: Package supporting the parsing, manipulating, and generating email messages.") package was updated to version 3.0, which dropped various deprecated APIs and removes support for Python versions earlier than 2.3. The 3.0 version of the package uses a new incremental parser for MIME messages, available in the `email.FeedParser` module. The new parser doesn't require reading the entire message into memory, and doesn't raise exceptions if a message is malformed; instead it records any problems in the `defect`attribute of the message. (Developed by Anthony Baxter, Barry Warsaw, Thomas Wouters, and others.)
- The [`heapq`](../library/heapq.xhtml#module-heapq "heapq: Heap queue algorithm (a.k.a. priority queue).") module has been converted to C. The resulting tenfold improvement in speed makes the module suitable for handling high volumes of data. In addition, the module has two new functions `nlargest()` and `nsmallest()` that use heaps to find the N largest or smallest values in a dataset without the expense of a full sort. (Contributed by Raymond Hettinger.)
- The `httplib` module now contains constants for HTTP status codes defined in various HTTP-related RFC documents. Constants have names such as `OK`, `CREATED`, `CONTINUE`, and `MOVED_PERMANENTLY`; use pydoc to get a full list. (Contributed by Andrew Eland.)
- The [`imaplib`](../library/imaplib.xhtml#module-imaplib "imaplib: IMAP4 protocol client (requires sockets).") module now supports IMAP's THREAD command (contributed by Yves Dionne) and new `deleteacl()` and `myrights()` methods (contributed by Arnaud Mazin).
- The [`itertools`](../library/itertools.xhtml#module-itertools "itertools: Functions creating iterators for efficient looping.") module gained a `groupby(iterable[, *func*])`function. *iterable* is something that can be iterated over to return a stream of elements, and the optional *func* parameter is a function that takes an element and returns a key value; if omitted, the key is simply the element itself. `groupby()` then groups the elements into subsequences which have matching values of the key, and returns a series of 2-tuples containing the key value and an iterator over the subsequence.
Here's an example to make this clearer. The *key* function simply returns whether a number is even or odd, so the result of `groupby()` is to return consecutive runs of odd or even numbers.
```
>>> import itertools
>>> L = [2, 4, 6, 7, 8, 9, 11, 12, 14]
>>> for key_val, it in itertools.groupby(L, lambda x: x % 2):
... print key_val, list(it)
...
0 [2, 4, 6]
1 [7]
0 [8]
1 [9, 11]
0 [12, 14]
>>>
```
`groupby()` is typically used with sorted input. The logic for `groupby()` is similar to the Unix `uniq` filter which makes it handy for eliminating, counting, or identifying duplicate elements:
```
>>> word = 'abracadabra'
>>> letters = sorted(word) # Turn string into a sorted list of letters
>>> letters
['a', 'a', 'a', 'a', 'a', 'b', 'b', 'c', 'd', 'r', 'r']
>>> for k, g in itertools.groupby(letters):
... print k, list(g)
...
a ['a', 'a', 'a', 'a', 'a']
b ['b', 'b']
c ['c']
d ['d']
r ['r', 'r']
>>> # List unique letters
>>> [k for k, g in groupby(letters)]
['a', 'b', 'c', 'd', 'r']
>>> # Count letter occurrences
>>> [(k, len(list(g))) for k, g in groupby(letters)]
[('a', 5), ('b', 2), ('c', 1), ('d', 1), ('r', 2)]
```
(Contributed by Hye-Shik Chang.)
- [`itertools`](../library/itertools.xhtml#module-itertools "itertools: Functions creating iterators for efficient looping.") also gained a function named `tee(iterator, N)` that returns *N* independent iterators that replicate *iterator*. If *N* is omitted, the default is 2.
```
>>> L = [1,2,3]
>>> i1, i2 = itertools.tee(L)
>>> i1,i2
(<itertools.tee object at 0x402c2080>, <itertools.tee object at 0x402c2090>)
>>> list(i1) # Run the first iterator to exhaustion
[1, 2, 3]
>>> list(i2) # Run the second iterator to exhaustion
[1, 2, 3]
```
Note that `tee()` has to keep copies of the values returned by the iterator; in the worst case, it may need to keep all of them. This should therefore be used carefully if the leading iterator can run far ahead of the trailing iterator in a long stream of inputs. If the separation is large, then you might as well use [`list()`](../library/stdtypes.xhtml#list "list") instead. When the iterators track closely with one another, `tee()` is ideal. Possible applications include bookmarking, windowing, or lookahead iterators. (Contributed by Raymond Hettinger.)
- A number of functions were added to the [`locale`](../library/locale.xhtml#module-locale "locale: Internationalization services.") module, such as `bind_textdomain_codeset()` to specify a particular encoding and a family of `l*gettext()` functions that return messages in the chosen encoding. (Contributed by Gustavo Niemeyer.)
- Some keyword arguments were added to the [`logging`](../library/logging.xhtml#module-logging "logging: Flexible event logging system for applications.") package's `basicConfig()` function to simplify log configuration. The default behavior is to log messages to standard error, but various keyword arguments can be specified to log to a particular file, change the logging format, or set the logging level. For example:
```
import logging
logging.basicConfig(filename='/var/log/application.log',
level=0, # Log all messages
format='%(levelname):%(process):%(thread):%(message)')
```
Other additions to the [`logging`](../library/logging.xhtml#module-logging "logging: Flexible event logging system for applications.") package include a `log(level, msg)`convenience method, as well as a `TimedRotatingFileHandler` class that rotates its log files at a timed interval. The module already had `RotatingFileHandler`, which rotated logs once the file exceeded a certain size. Both classes derive from a new `BaseRotatingHandler` class that can be used to implement other rotating handlers.
(Changes implemented by Vinay Sajip.)
- The [`marshal`](../library/marshal.xhtml#module-marshal "marshal: Convert Python objects to streams of bytes and back (with different constraints).") module now shares interned strings on unpacking a data structure. This may shrink the size of certain pickle strings, but the primary effect is to make `.pyc` files significantly smaller. (Contributed by Martin von L?wis.)
- The [`nntplib`](../library/nntplib.xhtml#module-nntplib "nntplib: NNTP protocol client (requires sockets).") module's `NNTP` class gained `description()` and `descriptions()` methods to retrieve newsgroup descriptions for a single group or for a range of groups. (Contributed by Jürgen A. Erhard.)
- Two new functions were added to the [`operator`](../library/operator.xhtml#module-operator "operator: Functions corresponding to the standard operators.") module, `attrgetter(attr)` and `itemgetter(index)`. Both functions return callables that take a single argument and return the corresponding attribute or item; these callables make excellent data extractors when used with [`map()`](../library/functions.xhtml#map "map")or [`sorted()`](../library/functions.xhtml#sorted "sorted"). For example:
```
>>> L = [('c', 2), ('d', 1), ('a', 4), ('b', 3)]
>>> map(operator.itemgetter(0), L)
['c', 'd', 'a', 'b']
>>> map(operator.itemgetter(1), L)
[2, 1, 4, 3]
>>> sorted(L, key=operator.itemgetter(1)) # Sort list by second tuple item
[('d', 1), ('c', 2), ('b', 3), ('a', 4)]
```
(Contributed by Raymond Hettinger.)
- The [`optparse`](../library/optparse.xhtml#module-optparse "optparse: Command-line option parsing library. (已移除)") module was updated in various ways. The module now passes its messages through [`gettext.gettext()`](../library/gettext.xhtml#gettext.gettext "gettext.gettext"), making it possible to internationalize Optik's help and error messages. Help messages for options can now include the string `'%default'`, which will be replaced by the option's default value. (Contributed by Greg Ward.)
- The long-term plan is to deprecate the `rfc822` module in some future Python release in favor of the [`email`](../library/email.xhtml#module-email "email: Package supporting the parsing, manipulating, and generating email messages.") package. To this end, the `email.Utils.formatdate()` function has been changed to make it usable as a replacement for `rfc822.formatdate()`. You may want to write new e-mail processing code with this in mind. (Change implemented by Anthony Baxter.)
- A new `urandom(n)` function was added to the [`os`](../library/os.xhtml#module-os "os: Miscellaneous operating system interfaces.") module, returning a string containing *n* bytes of random data. This function provides access to platform-specific sources of randomness such as `/dev/urandom` on Linux or the Windows CryptoAPI. (Contributed by Trevor Perrin.)
- Another new function: `os.path.lexists(path)` returns true if the file specified by *path* exists, whether or not it's a symbolic link. This differs from the existing `os.path.exists(path)` function, which returns false if *path* is a symlink that points to a destination that doesn't exist. (Contributed by Beni Cherniavsky.)
- A new `getsid()` function was added to the [`posix`](../library/posix.xhtml#module-posix "posix: The most common POSIX system calls (normally used via module os). (Unix)") module that underlies the [`os`](../library/os.xhtml#module-os "os: Miscellaneous operating system interfaces.") module. (Contributed by J. Raynor.)
- The [`poplib`](../library/poplib.xhtml#module-poplib "poplib: POP3 protocol client (requires sockets).") module now supports POP over SSL. (Contributed by Hector Urtubia.)
- The [`profile`](../library/profile.xhtml#module-profile "profile: Python source profiler.") module can now profile C extension functions. (Contributed by Nick Bastin.)
- The [`random`](../library/random.xhtml#module-random "random: Generate pseudo-random numbers with various common distributions.") module has a new method called `getrandbits(N)` that returns a long integer *N* bits in length. The existing `randrange()`method now uses `getrandbits()` where appropriate, making generation of arbitrarily large random numbers more efficient. (Contributed by Raymond Hettinger.)
- The regular expression language accepted by the [`re`](../library/re.xhtml#module-re "re: Regular expression operations.") module was extended with simple conditional expressions, written as `(?(group)A|B)`. *group* is either a numeric group ID or a group name defined with `(?P<group>...)`earlier in the expression. If the specified group matched, the regular expression pattern *A* will be tested against the string; if the group didn't match, the pattern *B* will be used instead. (Contributed by Gustavo Niemeyer.)
- The [`re`](../library/re.xhtml#module-re "re: Regular expression operations.") module is also no longer recursive, thanks to a massive amount of work by Gustavo Niemeyer. In a recursive regular expression engine, certain patterns result in a large amount of C stack space being consumed, and it was possible to overflow the stack. For example, if you matched a 30000-byte string of `a` characters against the expression `(a|b)+`, one stack frame was consumed per character. Python 2.3 tried to check for stack overflow and raise a [`RuntimeError`](../library/exceptions.xhtml#RuntimeError "RuntimeError") exception, but certain patterns could sidestep the checking and if you were unlucky Python could segfault. Python 2.4's regular expression engine can match this pattern without problems.
- The [`signal`](../library/signal.xhtml#module-signal "signal: Set handlers for asynchronous events.") module now performs tighter error-checking on the parameters to the [`signal.signal()`](../library/signal.xhtml#signal.signal "signal.signal") function. For example, you can't set a handler on the `SIGKILL` signal; previous versions of Python would quietly accept this, but 2.4 will raise a [`RuntimeError`](../library/exceptions.xhtml#RuntimeError "RuntimeError") exception.
- Two new functions were added to the [`socket`](../library/socket.xhtml#module-socket "socket: Low-level networking interface.") module. `socketpair()`returns a pair of connected sockets and `getservbyport(port)` looks up the service name for a given port number. (Contributed by Dave Cole and Barry Warsaw.)
- The `sys.exitfunc()` function has been deprecated. Code should be using the existing [`atexit`](../library/atexit.xhtml#module-atexit "atexit: Register and execute cleanup functions.") module, which correctly handles calling multiple exit functions. Eventually `sys.exitfunc()` will become a purely internal interface, accessed only by [`atexit`](../library/atexit.xhtml#module-atexit "atexit: Register and execute cleanup functions.").
- The [`tarfile`](../library/tarfile.xhtml#module-tarfile "tarfile: Read and write tar-format archive files.") module now generates GNU-format tar files by default. (Contributed by Lars Gust?bel.)
- The [`threading`](../library/threading.xhtml#module-threading "threading: Thread-based parallelism.") module now has an elegantly simple way to support thread-local data. The module contains a `local` class whose attribute values are local to different threads.
```
import threading
data = threading.local()
data.number = 42
data.url = ('www.python.org', 80)
```
Other threads can assign and retrieve their own values for the `number`and `url` attributes. You can subclass `local` to initialize attributes or to add methods. (Contributed by Jim Fulton.)
- The [`timeit`](../library/timeit.xhtml#module-timeit "timeit: Measure the execution time of small code snippets.") module now automatically disables periodic garbage collection during the timing loop. This change makes consecutive timings more comparable. (Contributed by Raymond Hettinger.)
- The [`weakref`](../library/weakref.xhtml#module-weakref "weakref: Support for weak references and weak dictionaries.") module now supports a wider variety of objects including Python functions, class instances, sets, frozensets, deques, arrays, files, sockets, and regular expression pattern objects. (Contributed by Raymond Hettinger.)
- The `xmlrpclib` module now supports a multi-call extension for transmitting multiple XML-RPC calls in a single HTTP operation. (Contributed by Brian Quinlan.)
- The `mpz`, `rotor`, and `xreadlines` modules have been removed.
### cookielib
The `cookielib` library supports client-side handling for HTTP cookies, mirroring the `Cookie` module's server-side cookie support. Cookies are stored in cookie jars; the library transparently stores cookies offered by the web server in the cookie jar, and fetches the cookie from the jar when connecting to the server. As in web browsers, policy objects control whether cookies are accepted or not.
In order to store cookies across sessions, two implementations of cookie jars are provided: one that stores cookies in the Netscape format so applications can use the Mozilla or Lynx cookie files, and one that stores cookies in the same format as the Perl libwww library.
`urllib2` has been changed to interact with `cookielib`: `HTTPCookieProcessor` manages a cookie jar that is used when accessing URLs.
This module was contributed by John J. Lee.
### doctest
The [`doctest`](../library/doctest.xhtml#module-doctest "doctest: Test pieces of code within docstrings.") module underwent considerable refactoring thanks to Edward Loper and Tim Peters. Testing can still be as simple as running [`doctest.testmod()`](../library/doctest.xhtml#doctest.testmod "doctest.testmod"), but the refactorings allow customizing the module's operation in various ways
The new `DocTestFinder` class extracts the tests from a given object's docstrings:
```
def f (x, y):
""">>> f(2,2)
4
>>> f(3,2)
6
"""
return x*y
finder = doctest.DocTestFinder()
# Get list of DocTest instances
tests = finder.find(f)
```
The new `DocTestRunner` class then runs individual tests and can produce a summary of the results:
```
runner = doctest.DocTestRunner()
for t in tests:
tried, failed = runner.run(t)
runner.summarize(verbose=1)
```
The above example produces the following output:
```
1 items passed all tests:
2 tests in f
2 tests in 1 items.
2 passed and 0 failed.
Test passed.
```
`DocTestRunner` uses an instance of the `OutputChecker` class to compare the expected output with the actual output. This class takes a number of different flags that customize its behaviour; ambitious users can also write a completely new subclass of `OutputChecker`.
The default output checker provides a number of handy features. For example, with the [`doctest.ELLIPSIS`](../library/doctest.xhtml#doctest.ELLIPSIS "doctest.ELLIPSIS") option flag, an ellipsis (`...`) in the expected output matches any substring, making it easier to accommodate outputs that vary in minor ways:
```
def o (n):
""">>> o(1)
<__main__.C instance at 0x...>
>>>
"""
```
Another special string, `<BLANKLINE>`, matches a blank line:
```
def p (n):
""">>> p(1)
<BLANKLINE>
>>>
"""
```
Another new capability is producing a diff-style display of the output by specifying the [`doctest.REPORT_UDIFF`](../library/doctest.xhtml#doctest.REPORT_UDIFF "doctest.REPORT_UDIFF") (unified diffs), [`doctest.REPORT_CDIFF`](../library/doctest.xhtml#doctest.REPORT_CDIFF "doctest.REPORT_CDIFF") (context diffs), or [`doctest.REPORT_NDIFF`](../library/doctest.xhtml#doctest.REPORT_NDIFF "doctest.REPORT_NDIFF")(delta-style) option flags. For example:
```
def g (n):
""">>> g(4)
here
is
a
lengthy
>>>"""
L = 'here is a rather lengthy list of words'.split()
for word in L[:n]:
print word
```
Running the above function's tests with [`doctest.REPORT_UDIFF`](../library/doctest.xhtml#doctest.REPORT_UDIFF "doctest.REPORT_UDIFF") specified, you get the following output:
```
**********************************************************************
File "t.py", line 15, in g
Failed example:
g(4)
Differences (unified diff with -expected +actual):
@@ -2,3 +2,3 @@
is
a
-lengthy
+rather
**********************************************************************
```
## Build and C API Changes
Some of the changes to Python's build process and to the C API are:
- Three new convenience macros were added for common return values from extension functions: [`Py_RETURN_NONE`](../c-api/none.xhtml#c.Py_RETURN_NONE "Py_RETURN_NONE"), [`Py_RETURN_TRUE`](../c-api/bool.xhtml#c.Py_RETURN_TRUE "Py_RETURN_TRUE"), and [`Py_RETURN_FALSE`](../c-api/bool.xhtml#c.Py_RETURN_FALSE "Py_RETURN_FALSE"). (Contributed by Brett Cannon.)
- Another new macro, `Py_CLEAR(obj)`, decreases the reference count of *obj* and sets *obj* to the null pointer. (Contributed by Jim Fulton.)
- A new function, `PyTuple_Pack(N, obj1, obj2, ..., objN)`, constructs tuples from a variable length argument list of Python objects. (Contributed by Raymond Hettinger.)
- A new function, `PyDict_Contains(d, k)`, implements fast dictionary lookups without masking exceptions raised during the look-up process. (Contributed by Raymond Hettinger.)
- The `Py_IS_NAN(X)` macro returns 1 if its float or double argument *X* is a NaN. (Contributed by Tim Peters.)
- C code can avoid unnecessary locking by using the new [`PyEval_ThreadsInitialized()`](../c-api/init.xhtml#c.PyEval_ThreadsInitialized "PyEval_ThreadsInitialized") function to tell if any thread operations have been performed. If this function returns false, no lock operations are needed. (Contributed by Nick Coghlan.)
- A new function, [`PyArg_VaParseTupleAndKeywords()`](../c-api/arg.xhtml#c.PyArg_VaParseTupleAndKeywords "PyArg_VaParseTupleAndKeywords"), is the same as [`PyArg_ParseTupleAndKeywords()`](../c-api/arg.xhtml#c.PyArg_ParseTupleAndKeywords "PyArg_ParseTupleAndKeywords") but takes a `va_list` instead of a number of arguments. (Contributed by Greg Chapman.)
- A new method flag, `METH_COEXISTS`, allows a function defined in slots to co-exist with a [`PyCFunction`](../c-api/structures.xhtml#c.PyCFunction "PyCFunction") having the same name. This can halve the access time for a method such as `set.__contains__()`. (Contributed by Raymond Hettinger.)
- Python can now be built with additional profiling for the interpreter itself, intended as an aid to people developing the Python core. Providing `--enable-profiling` to the **configure** script will let you profile the interpreter with **gprof**, and providing the `--with-tsc` switch enables profiling using the Pentium's Time-Stamp-Counter register. Note that the `--with-tsc` switch is slightly misnamed, because the profiling feature also works on the PowerPC platform, though that processor architecture doesn't call that register "the TSC register". (Contributed by Jeremy Hylton.)
- The `tracebackobject` type has been renamed to `PyTracebackObject`.
### Port-Specific Changes
- The Windows port now builds under MSVC++ 7.1 as well as version 6. (Contributed by Martin von L?wis.)
## Porting to Python 2.4
This section lists previously described changes that may require changes to your code:
- Left shifts and hexadecimal/octal constants that are too large no longer trigger a [`FutureWarning`](../library/exceptions.xhtml#FutureWarning "FutureWarning") and return a value limited to 32 or 64 bits; instead they return a long integer.
- Integer operations will no longer trigger an `OverflowWarning`. The `OverflowWarning` warning will disappear in Python 2.5.
- The [`zip()`](../library/functions.xhtml#zip "zip") built-in function and `itertools.izip()` now return an empty list instead of raising a [`TypeError`](../library/exceptions.xhtml#TypeError "TypeError") exception if called with no arguments.
- You can no longer compare the `date` and [`datetime`](../library/datetime.xhtml#datetime.datetime "datetime.datetime") instances provided by the [`datetime`](../library/datetime.xhtml#module-datetime "datetime: Basic date and time types.") module. Two instances of different classes will now always be unequal, and relative comparisons (`<`, `>`) will raise a [`TypeError`](../library/exceptions.xhtml#TypeError "TypeError").
- `dircache.listdir()` now passes exceptions to the caller instead of returning empty lists.
- `LexicalHandler.startDTD()` used to receive the public and system IDs in the wrong order. This has been corrected; applications relying on the wrong order need to be fixed.
- [`fcntl.ioctl()`](../library/fcntl.xhtml#fcntl.ioctl "fcntl.ioctl") now warns if the *mutate* argument is omitted and relevant.
- The [`tarfile`](../library/tarfile.xhtml#module-tarfile "tarfile: Read and write tar-format archive files.") module now generates GNU-format tar files by default.
- Encountering a failure while importing a module no longer leaves a partially-initialized module object in `sys.modules`.
- [`None`](../library/constants.xhtml#None "None") is now a constant; code that binds a new value to the name `None` is now a syntax error.
- The `signals.signal()` function now raises a [`RuntimeError`](../library/exceptions.xhtml#RuntimeError "RuntimeError") exception for certain illegal values; previously these errors would pass silently. For example, you can no longer set a handler on the `SIGKILL` signal.
## Acknowledgements
The author would like to thank the following people for offering suggestions, corrections and assistance with various drafts of this article: Koray Can, Hye-Shik Chang, Michael Dyck, Raymond Hettinger, Brian Hurt, Hamish Lawson, Fredrik Lundh, Sean Reifschneider, Sadruddin Rejeb.
### 導航
- [索引](../genindex.xhtml "總目錄")
- [模塊](../py-modindex.xhtml "Python 模塊索引") |
- [下一頁](2.3.xhtml "What's New in Python 2.3") |
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- [Python](https://www.python.org/) ?
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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?
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