Argparse 教程 · Python3.7.3官方文檔簡體中文

### 導航 - [索引](../genindex.xhtml "總目錄") - [模塊](../py-modindex.xhtml "Python 模塊索引") | - [下一頁](ipaddress.xhtml "ipaddress模塊介紹") | - [上一頁](urllib2.xhtml "如何使用urllib包獲取網絡資源") | - ![](https://box.kancloud.cn/a721fc7ec672275e257bbbfde49a4d4e_16x16.png) - [Python](https://www.python.org/) ? - zh\_CN 3.7.3 [文檔](../index.xhtml) ? - [Python 常用指引](index.xhtml) ? - $('.inline-search').show(0); | # Argparse 教程作者Tshepang Lekhonkhobe 這篇教程旨在作為 [`argparse`](../library/argparse.xhtml#module-argparse "argparse: Command-line option and argument parsing library.") 的入門介紹，此模塊是 Python 標準庫中推薦的命令行解析模塊。注解還有另外兩個模塊可以完成同樣的任務，它們的名字是 [`getopt`](../library/getopt.xhtml#module-getopt "getopt: Portable parser for command line options; support both short and long option names.") (對應于 C 語言中的 `getopt()` 函數) 以及已棄用的 [`optparse`](../library/optparse.xhtml#module-optparse "optparse: Command-line option parsing library. (已移除)"). 還要注意 [`argparse`](../library/argparse.xhtml#module-argparse "argparse: Command-line option and argument parsing library.") 是基于 [`optparse`](../library/optparse.xhtml#module-optparse "optparse: Command-line option parsing library. (已移除)") 的，因此在用法上與其非常相似。 ## 概念讓我們通過使用 **ls** 命令來展示我們將在本入門教程中探索的功能： ``` $ ls cpython devguide prog.py pypy rm-unused-function.patch $ ls pypy ctypes_configure demo dotviewer include lib_pypy lib-python ... $ ls -l total 20 drwxr-xr-x 19 wena wena 4096 Feb 18 18:51 cpython drwxr-xr-x 4 wena wena 4096 Feb 8 12:04 devguide -rwxr-xr-x 1 wena wena 535 Feb 19 00:05 prog.py drwxr-xr-x 14 wena wena 4096 Feb 7 00:59 pypy -rw-r--r-- 1 wena wena 741 Feb 18 01:01 rm-unused-function.patch $ ls --help Usage: ls [OPTION]... [FILE]... List information about the FILEs (the current directory by default). Sort entries alphabetically if none of -cftuvSUX nor --sort is specified. ... ``` 我們可以從這四個命令中學到幾個概念： - **ls** 是一個即使在運行的時候沒有提供任何選項，也非常有用的命令。在默認情況下他會輸出當前文件夾包含的文件和文件夾。 - 如果我們想要使用比它默認提供的更多功能，我們需要告訴該命令更多信息。在這個例子里，我們想要查看一個不同的目錄，`pypy`。我們所做的是指定所謂的位置參數。之所以這樣命名，是因為程序應該如何處理該參數值，完全取決于它在命令行出現的位置。更能體現這個概念的命令如 **cp**，它最基本的用法是 `cp SRC DEST`。第一個位置參數指的是\*你想要復制的\*，第二個位置參數指的是\*你想要復制到的位置\*。 - 現在假設我們想要改變這個程序的行為。在我們的例子中，我們不僅僅只是輸出每個文件的文件名，還輸出了更多信息。在這個例子中，`-l` 被稱為可選參數。 - 這是一段幫助文檔的文字。它是非常有用的，因為當你遇到一個你從未使用過的程序時，你可以通過閱讀它的幫助文檔來弄清楚它是如何運行的。 ## 基礎讓我們從一個非常簡單的例子開始： ``` import argparse parser = argparse.ArgumentParser() parser.parse_args() ``` 以下是該代碼的運行結果： ``` $ python3 prog.py $ python3 prog.py --help usage: prog.py [-h] optional arguments: -h, --help show this help message and exit $ python3 prog.py --verbose usage: prog.py [-h] prog.py: error: unrecognized arguments: --verbose $ python3 prog.py foo usage: prog.py [-h] prog.py: error: unrecognized arguments: foo ``` 程序運行情況如下： - 在沒有任何選項的情況下運行腳本不會在標準輸出顯示任何內容。這沒有什么用處。 - 第二行代碼開始展現出 [`argparse`](../library/argparse.xhtml#module-argparse "argparse: Command-line option and argument parsing library.") 模塊的作用。我們幾乎什么也沒有做，但已經得到一條很好的幫助信息。 - `--help``選項，也可縮寫為`-h``，是唯一一個可以免費獲得的選項（即不需要指定該選項的內容）。指定任何內容會導致錯誤。即便如此，我們也能免費得到一條有用的用法信息。 ## 位置參數介紹舉個例子： ``` import argparse parser = argparse.ArgumentParser() parser.add_argument("echo") args = parser.parse_args() print(args.echo) ``` 運行此程序： ``` $ python3 prog.py usage: prog.py [-h] echo prog.py: error: the following arguments are required: echo $ python3 prog.py --help usage: prog.py [-h] echo positional arguments: echo optional arguments: -h, --help show this help message and exit $ python3 prog.py foo foo ``` 程序運行情況如下： - 我們添加了 `add_argument()` 方法，該方法用于指定程序能夠接受哪些命令行選項。在這個例子中，我將選項命名為``echo``，與它的功能相一致。 - 現在調用我們的程序必須要指定一個選項。 - The `parse_args()` method actually returns some data from the options specified, in this case, `echo`. - The variable is some form of 'magic' that [`argparse`](../library/argparse.xhtml#module-argparse "argparse: Command-line option and argument parsing library.") performs for free (i.e. no need to specify which variable that value is stored in). You will also notice that its name matches the string argument given to the method, `echo`. Note however that, although the help display looks nice and all, it currently is not as helpful as it can be. For example we see that we got `echo` as a positional argument, but we don't know what it does, other than by guessing or by reading the source code. So, let's make it a bit more useful: ``` import argparse parser = argparse.ArgumentParser() parser.add_argument("echo", help="echo the string you use here") args = parser.parse_args() print(args.echo) ``` And we get: ``` $ python3 prog.py -h usage: prog.py [-h] echo positional arguments: echo echo the string you use here optional arguments: -h, --help show this help message and exit ``` Now, how about doing something even more useful: ``` import argparse parser = argparse.ArgumentParser() parser.add_argument("square", help="display a square of a given number") args = parser.parse_args() print(args.square**2) ``` 以下是該代碼的運行結果： ``` $ python3 prog.py 4 Traceback (most recent call last): File "prog.py", line 5, in <module> print(args.square**2) TypeError: unsupported operand type(s) for ** or pow(): 'str' and 'int' ``` That didn't go so well. That's because [`argparse`](../library/argparse.xhtml#module-argparse "argparse: Command-line option and argument parsing library.") treats the options we give it as strings, unless we tell it otherwise. So, let's tell [`argparse`](../library/argparse.xhtml#module-argparse "argparse: Command-line option and argument parsing library.") to treat that input as an integer: ``` import argparse parser = argparse.ArgumentParser() parser.add_argument("square", help="display a square of a given number", type=int) args = parser.parse_args() print(args.square**2) ``` 以下是該代碼的運行結果： ``` $ python3 prog.py 4 16 $ python3 prog.py four usage: prog.py [-h] square prog.py: error: argument square: invalid int value: 'four' ``` That went well. The program now even helpfully quits on bad illegal input before proceeding. ## Introducing Optional arguments So far we have been playing with positional arguments. Let us have a look on how to add optional ones: ``` import argparse parser = argparse.ArgumentParser() parser.add_argument("--verbosity", help="increase output verbosity") args = parser.parse_args() if args.verbosity: print("verbosity turned on") ``` And the output: ``` $ python3 prog.py --verbosity 1 verbosity turned on $ python3 prog.py $ python3 prog.py --help usage: prog.py [-h] [--verbosity VERBOSITY] optional arguments: -h, --help show this help message and exit --verbosity VERBOSITY increase output verbosity $ python3 prog.py --verbosity usage: prog.py [-h] [--verbosity VERBOSITY] prog.py: error: argument --verbosity: expected one argument ``` 程序運行情況如下： - The program is written so as to display something when `--verbosity` is specified and display nothing when not. - To show that the option is actually optional, there is no error when running the program without it. Note that by default, if an optional argument isn't used, the relevant variable, in this case `args.verbosity`, is given `None` as a value, which is the reason it fails the truth test of the [`if`](../reference/compound_stmts.xhtml#if) statement. - The help message is a bit different. - When using the `--verbosity` option, one must also specify some value, any value. The above example accepts arbitrary integer values for `--verbosity`, but for our simple program, only two values are actually useful, `True` or `False`. Let's modify the code accordingly: ``` import argparse parser = argparse.ArgumentParser() parser.add_argument("--verbose", help="increase output verbosity", action="store_true") args = parser.parse_args() if args.verbose: print("verbosity turned on") ``` And the output: ``` $ python3 prog.py --verbose verbosity turned on $ python3 prog.py --verbose 1 usage: prog.py [-h] [--verbose] prog.py: error: unrecognized arguments: 1 $ python3 prog.py --help usage: prog.py [-h] [--verbose] optional arguments: -h, --help show this help message and exit --verbose increase output verbosity ``` 程序運行情況如下： - The option is now more of a flag than something that requires a value. We even changed the name of the option to match that idea. Note that we now specify a new keyword, `action`, and give it the value `"store_true"`. This means that, if the option is specified, assign the value `True` to `args.verbose`. Not specifying it implies `False`. - It complains when you specify a value, in true spirit of what flags actually are. - Notice the different help text. ### Short options If you are familiar with command line usage, you will notice that I haven't yet touched on the topic of short versions of the options. It's quite simple: ``` import argparse parser = argparse.ArgumentParser() parser.add_argument("-v", "--verbose", help="increase output verbosity", action="store_true") args = parser.parse_args() if args.verbose: print("verbosity turned on") ``` And here goes: ``` $ python3 prog.py -v verbosity turned on $ python3 prog.py --help usage: prog.py [-h] [-v] optional arguments: -h, --help show this help message and exit -v, --verbose increase output verbosity ``` Note that the new ability is also reflected in the help text. ## Combining Positional and Optional arguments Our program keeps growing in complexity: ``` import argparse parser = argparse.ArgumentParser() parser.add_argument("square", type=int, help="display a square of a given number") parser.add_argument("-v", "--verbose", action="store_true", help="increase output verbosity") args = parser.parse_args() answer = args.square**2 if args.verbose: print("the square of {} equals {}".format(args.square, answer)) else: print(answer) ``` And now the output: ``` $ python3 prog.py usage: prog.py [-h] [-v] square prog.py: error: the following arguments are required: square $ python3 prog.py 4 16 $ python3 prog.py 4 --verbose the square of 4 equals 16 $ python3 prog.py --verbose 4 the square of 4 equals 16 ``` - We've brought back a positional argument, hence the complaint. - Note that the order does not matter. How about we give this program of ours back the ability to have multiple verbosity values, and actually get to use them: ``` import argparse parser = argparse.ArgumentParser() parser.add_argument("square", type=int, help="display a square of a given number") parser.add_argument("-v", "--verbosity", type=int, help="increase output verbosity") args = parser.parse_args() answer = args.square**2 if args.verbosity == 2: print("the square of {} equals {}".format(args.square, answer)) elif args.verbosity == 1: print("{}^2 == {}".format(args.square, answer)) else: print(answer) ``` And the output: ``` $ python3 prog.py 4 16 $ python3 prog.py 4 -v usage: prog.py [-h] [-v VERBOSITY] square prog.py: error: argument -v/--verbosity: expected one argument $ python3 prog.py 4 -v 1 4^2 == 16 $ python3 prog.py 4 -v 2 the square of 4 equals 16 $ python3 prog.py 4 -v 3 16 ``` These all look good except the last one, which exposes a bug in our program. Let's fix it by restricting the values the `--verbosity` option can accept: ``` import argparse parser = argparse.ArgumentParser() parser.add_argument("square", type=int, help="display a square of a given number") parser.add_argument("-v", "--verbosity", type=int, choices=[0, 1, 2], help="increase output verbosity") args = parser.parse_args() answer = args.square**2 if args.verbosity == 2: print("the square of {} equals {}".format(args.square, answer)) elif args.verbosity == 1: print("{}^2 == {}".format(args.square, answer)) else: print(answer) ``` And the output: ``` $ python3 prog.py 4 -v 3 usage: prog.py [-h] [-v {0,1,2}] square prog.py: error: argument -v/--verbosity: invalid choice: 3 (choose from 0, 1, 2) $ python3 prog.py 4 -h usage: prog.py [-h] [-v {0,1,2}] square positional arguments: square display a square of a given number optional arguments: -h, --help show this help message and exit -v {0,1,2}, --verbosity {0,1,2} increase output verbosity ``` Note that the change also reflects both in the error message as well as the help string. Now, let's use a different approach of playing with verbosity, which is pretty common. It also matches the way the CPython executable handles its own verbosity argument (check the output of `python --help`): ``` import argparse parser = argparse.ArgumentParser() parser.add_argument("square", type=int, help="display the square of a given number") parser.add_argument("-v", "--verbosity", action="count", help="increase output verbosity") args = parser.parse_args() answer = args.square**2 if args.verbosity == 2: print("the square of {} equals {}".format(args.square, answer)) elif args.verbosity == 1: print("{}^2 == {}".format(args.square, answer)) else: print(answer) ``` We have introduced another action, "count", to count the number of occurrences of a specific optional arguments: ``` $ python3 prog.py 4 16 $ python3 prog.py 4 -v 4^2 == 16 $ python3 prog.py 4 -vv the square of 4 equals 16 $ python3 prog.py 4 --verbosity --verbosity the square of 4 equals 16 $ python3 prog.py 4 -v 1 usage: prog.py [-h] [-v] square prog.py: error: unrecognized arguments: 1 $ python3 prog.py 4 -h usage: prog.py [-h] [-v] square positional arguments: square display a square of a given number optional arguments: -h, --help show this help message and exit -v, --verbosity increase output verbosity $ python3 prog.py 4 -vvv 16 ``` - Yes, it's now more of a flag (similar to `action="store_true"`) in the previous version of our script. That should explain the complaint. - It also behaves similar to "store\_true" action. - Now here's a demonstration of what the "count" action gives. You've probably seen this sort of usage before. - And if you don't specify the `-v` flag, that flag is considered to have `None` value. - As should be expected, specifying the long form of the flag, we should get the same output. - Sadly, our help output isn't very informative on the new ability our script has acquired, but that can always be fixed by improving the documentation for our script (e.g. via the `help` keyword argument). - That last output exposes a bug in our program. Let's fix: ``` import argparse parser = argparse.ArgumentParser() parser.add_argument("square", type=int, help="display a square of a given number") parser.add_argument("-v", "--verbosity", action="count", help="increase output verbosity") args = parser.parse_args() answer = args.square**2 # bugfix: replace == with >= if args.verbosity >= 2: print("the square of {} equals {}".format(args.square, answer)) elif args.verbosity >= 1: print("{}^2 == {}".format(args.square, answer)) else: print(answer) ``` And this is what it gives: ``` $ python3 prog.py 4 -vvv the square of 4 equals 16 $ python3 prog.py 4 -vvvv the square of 4 equals 16 $ python3 prog.py 4 Traceback (most recent call last): File "prog.py", line 11, in <module> if args.verbosity >= 2: TypeError: '>=' not supported between instances of 'NoneType' and 'int' ``` - First output went well, and fixes the bug we had before. That is, we want any value >= 2 to be as verbose as possible. - Third output not so good. Let's fix that bug: ``` import argparse parser = argparse.ArgumentParser() parser.add_argument("square", type=int, help="display a square of a given number") parser.add_argument("-v", "--verbosity", action="count", default=0, help="increase output verbosity") args = parser.parse_args() answer = args.square**2 if args.verbosity >= 2: print("the square of {} equals {}".format(args.square, answer)) elif args.verbosity >= 1: print("{}^2 == {}".format(args.square, answer)) else: print(answer) ``` We've just introduced yet another keyword, `default`. We've set it to `0` in order to make it comparable to the other int values. Remember that by default, if an optional argument isn't specified, it gets the `None` value, and that cannot be compared to an int value (hence the [`TypeError`](../library/exceptions.xhtml#TypeError "TypeError") exception). And: ``` $ python3 prog.py 4 16 ``` You can go quite far just with what we've learned so far, and we have only scratched the surface. The [`argparse`](../library/argparse.xhtml#module-argparse "argparse: Command-line option and argument parsing library.") module is very powerful, and we'll explore a bit more of it before we end this tutorial. ## Getting a little more advanced What if we wanted to expand our tiny program to perform other powers, not just squares: ``` import argparse parser = argparse.ArgumentParser() parser.add_argument("x", type=int, help="the base") parser.add_argument("y", type=int, help="the exponent") parser.add_argument("-v", "--verbosity", action="count", default=0) args = parser.parse_args() answer = args.x**args.y if args.verbosity >= 2: print("{} to the power {} equals {}".format(args.x, args.y, answer)) elif args.verbosity >= 1: print("{}^{} == {}".format(args.x, args.y, answer)) else: print(answer) ``` Output: ``` $ python3 prog.py usage: prog.py [-h] [-v] x y prog.py: error: the following arguments are required: x, y $ python3 prog.py -h usage: prog.py [-h] [-v] x y positional arguments: x the base y the exponent optional arguments: -h, --help show this help message and exit -v, --verbosity $ python3 prog.py 4 2 -v 4^2 == 16 ``` Notice that so far we've been using verbosity level to *change* the text that gets displayed. The following example instead uses verbosity level to display *more* text instead: ``` import argparse parser = argparse.ArgumentParser() parser.add_argument("x", type=int, help="the base") parser.add_argument("y", type=int, help="the exponent") parser.add_argument("-v", "--verbosity", action="count", default=0) args = parser.parse_args() answer = args.x**args.y if args.verbosity >= 2: print("Running '{}'".format(__file__)) if args.verbosity >= 1: print("{}^{} == ".format(args.x, args.y), end="") print(answer) ``` Output: ``` $ python3 prog.py 4 2 16 $ python3 prog.py 4 2 -v 4^2 == 16 $ python3 prog.py 4 2 -vv Running 'prog.py' 4^2 == 16 ``` ### Conflicting options So far, we have been working with two methods of an [`argparse.ArgumentParser`](../library/argparse.xhtml#argparse.ArgumentParser "argparse.ArgumentParser") instance. Let's introduce a third one, `add_mutually_exclusive_group()`. It allows for us to specify options that conflict with each other. Let's also change the rest of the program so that the new functionality makes more sense: we'll introduce the `--quiet` option, which will be the opposite of the `--verbose` one: ``` import argparse parser = argparse.ArgumentParser() group = parser.add_mutually_exclusive_group() group.add_argument("-v", "--verbose", action="store_true") group.add_argument("-q", "--quiet", action="store_true") parser.add_argument("x", type=int, help="the base") parser.add_argument("y", type=int, help="the exponent") args = parser.parse_args() answer = args.x**args.y if args.quiet: print(answer) elif args.verbose: print("{} to the power {} equals {}".format(args.x, args.y, answer)) else: print("{}^{} == {}".format(args.x, args.y, answer)) ``` Our program is now simpler, and we've lost some functionality for the sake of demonstration. Anyways, here's the output: ``` $ python3 prog.py 4 2 4^2 == 16 $ python3 prog.py 4 2 -q 16 $ python3 prog.py 4 2 -v 4 to the power 2 equals 16 $ python3 prog.py 4 2 -vq usage: prog.py [-h] [-v | -q] x y prog.py: error: argument -q/--quiet: not allowed with argument -v/--verbose $ python3 prog.py 4 2 -v --quiet usage: prog.py [-h] [-v | -q] x y prog.py: error: argument -q/--quiet: not allowed with argument -v/--verbose ``` That should be easy to follow. I've added that last output so you can see the sort of flexibility you get, i.e. mixing long form options with short form ones. Before we conclude, you probably want to tell your users the main purpose of your program, just in case they don't know: ``` import argparse parser = argparse.ArgumentParser(description="calculate X to the power of Y") group = parser.add_mutually_exclusive_group() group.add_argument("-v", "--verbose", action="store_true") group.add_argument("-q", "--quiet", action="store_true") parser.add_argument("x", type=int, help="the base") parser.add_argument("y", type=int, help="the exponent") args = parser.parse_args() answer = args.x**args.y if args.quiet: print(answer) elif args.verbose: print("{} to the power {} equals {}".format(args.x, args.y, answer)) else: print("{}^{} == {}".format(args.x, args.y, answer)) ``` Note that slight difference in the usage text. Note the `[-v | -q]`, which tells us that we can either use `-v` or `-q`, but not both at the same time: ``` $ python3 prog.py --help usage: prog.py [-h] [-v | -q] x y calculate X to the power of Y positional arguments: x the base y the exponent optional arguments: -h, --help show this help message and exit -v, --verbose -q, --quiet ``` ## Conclusion The [`argparse`](../library/argparse.xhtml#module-argparse "argparse: Command-line option and argument parsing library.") module offers a lot more than shown here. Its docs are quite detailed and thorough, and full of examples. Having gone through this tutorial, you should easily digest them without feeling overwhelmed. ### 導航 - [索引](../genindex.xhtml "總目錄") - [模塊](../py-modindex.xhtml "Python 模塊索引") | - [下一頁](ipaddress.xhtml "ipaddress模塊介紹") | - [上一頁](urllib2.xhtml "如何使用urllib包獲取網絡資源") | - ![](https://box.kancloud.cn/a721fc7ec672275e257bbbfde49a4d4e_16x16.png) - [Python](https://www.python.org/) ? - zh\_CN 3.7.3 [文檔](../index.xhtml) ? - [Python 常用指引](index.xhtml) ? - $('.inline-search').show(0); | ? [版權所有](../copyright.xhtml) 2001-2019, Python Software Foundation. Python 軟件基金會是一個非盈利組織。 [請捐助。](https://www.python.org/psf/donations/) 最后更新于 5月 21, 2019. [發現了問題](../bugs.xhtml)？使用[Sphinx](http://sphinx.pocoo.org/)1.8.4 創建。