Python Argparse：“可选参数”下列出的必需参数？

Argparse: Required arguments listed under "optional arguments"?

提问by mort

I use the following simple code to parse some arguments; note that one of them is required. Unfortunately, when the user runs the script without providing the argument, the displayed usage/help text does not indicate that there is a non-optional argument, which I find very confusing. How can I get python to indicate that an argument is not optional?

我使用以下简单代码来解析一些参数；请注意，其中之一是必需的。不幸的是，当用户在没有提供参数的情况下运行脚本时，显示的用法/帮助文本并不表示存在非可选参数，我觉得这很令人困惑。我怎样才能让 python 表明一个参数不是可选的？

Here is the code:

这是代码：

import argparse
if __name__ == '__main__':
    parser = argparse.ArgumentParser(
        description='Foo')
    parser.add_argument('-i','--input', help='Input file name', required=True)
    parser.add_argument('-o','--output', help='Output file name', default="stdout")
    args = parser.parse_args()
    print ("Input file: %s" % args.input )
    print ("Output file: %s" % args.output )

When running above code without providing the required argument, I get the following output:

在不提供所需参数的情况下运行上面的代码时，我得到以下输出：

usage: foo.py [-h] -i INPUT [-o OUTPUT]

Foo

optional arguments:
    -h, --help            show this help message and exit
    -i INPUT, --input INPUT
                          Input file name
    -o OUTPUT, --output OUTPUT
                          Output file name

采纳答案by poke

Parameters starting with -or --are usually considered optional. All other parameters are positional parameters and as such required by design (like positional function arguments). It is possible to require optional arguments, but this is a bit against their design. Since they are still part of the non-positional arguments, they will still be listed under the confusing header “optional arguments” even if they are required. The missing square brackets in the usage part however show that they are indeed required.

以-或开头的参数--通常被认为是可选的。所有其他参数都是位置参数，因此是设计所必需的（如位置函数参数）。可能需要可选参数，但这有点违背他们的设计。由于它们仍然是非位置参数的一部分，即使它们是必需的，它们仍将列在令人困惑的标题“可选参数”下。然而，使用部分缺少的方括号表明它们确实是必需的。

See also the documentation:

另请参阅文档：

In general, the argparse module assumes that flags like -f and --bar indicate optional arguments, which can always be omitted at the command line.

Note:Required options are generally considered bad form because users expect options to be optional, and thus they should be avoided when possible.

通常， argparse 模块假定像 -f 和 --bar 这样的标志表示可选参数，它们总是可以在命令行中省略。

注意：必需选项通常被认为是不好的形式，因为用户希望选项是可选的，因此应尽可能避免使用。

That being said, the headers “positional arguments”and “optional arguments”in the help are generated by two argument groups in which the arguments are automatically separated into. Now, you could “hack into it” and change the name of the optional ones, but a far more elegant solution would be to create another group for “required named arguments” (or whatever you want to call them):

话虽如此，帮助中的标题“位置参数”和“可选参数”是由两个参数组生成的，其中参数自动分成。现在，您可以“入侵它”并更改可选参数的名称，但更优雅的解决方案是为“必需的命名参数”（或您想调用的任何名称）创建另一个组：

parser = argparse.ArgumentParser(description='Foo')
parser.add_argument('-o', '--output', help='Output file name', default='stdout')
requiredNamed = parser.add_argument_group('required named arguments')
requiredNamed.add_argument('-i', '--input', help='Input file name', required=True)
parser.parse_args(['-h'])

usage: [-h] [-o OUTPUT] -i INPUT

Foo

optional arguments:
  -h, --help            show this help message and exit
  -o OUTPUT, --output OUTPUT
                        Output file name

required named arguments:
  -i INPUT, --input INPUT
                        Input file name

回答by Karl Rosaen

Since I prefer to list required arguments before optional, I hack around it via:

由于我更喜欢​​在可选参数之前列出必需参数，因此我通过以下方式绕过它：

    parser = argparse.ArgumentParser()
    parser._action_groups.pop()
    required = parser.add_argument_group('required arguments')
    optional = parser.add_argument_group('optional arguments')
    required.add_argument('--required_arg', required=True)
    optional.add_argument('--optional_arg')
    return parser.parse_args()

and this outputs:

这输出：

usage: main.py [-h] [--required_arg REQUIRED_ARG]
               [--optional_arg OPTIONAL_ARG]

required arguments:
  --required_arg REQUIRED_ARG

optional arguments:
  --optional_arg OPTIONAL_ARG

I can live without 'help' showing up in the optional arguments group.

我可以在没有“帮助”的情况下生活在可选参数组中。

回答by RalphyZ

Building off of @Karl Rosaen

建立在@Karl Rosaen

parser = argparse.ArgumentParser()
optional = parser._action_groups.pop() # Edited this line
required = parser.add_argument_group('required arguments')
# remove this line: optional = parser...
required.add_argument('--required_arg', required=True)
optional.add_argument('--optional_arg')
parser._action_groups.append(optional) # added this line
return parser.parse_args()

and this outputs:

这输出：

usage: main.py [-h] [--required_arg REQUIRED_ARG]
           [--optional_arg OPTIONAL_ARG]

required arguments:
  --required_arg REQUIRED_ARG

optional arguments:
  -h, --help                    show this help message and exit
  --optional_arg OPTIONAL_ARG

回答by Bryan_D

One more time, building off of @RalphyZ

再一次，建立在@RalphyZ 之上

This one doesn't break the exposed API.

这个不会破坏公开的 API。

from argparse import ArgumentParser, SUPPRESS
# Disable default help
parser = ArgumentParser(add_help=False)
required = parser.add_argument_group('required arguments')
optional = parser.add_argument_group('optional arguments')

# Add back help 
optional.add_argument(
    '-h',
    '--help',
    action='help',
    default=SUPPRESS,
    help='show this help message and exit'
)
required.add_argument('--required_arg', required=True)
optional.add_argument('--optional_arg')

Which will show the same as above and should survive future versions:

这将显示与上面相同的内容，并且应该在未来的版本中继续存在：

usage: main.py [-h] [--required_arg REQUIRED_ARG]
           [--optional_arg OPTIONAL_ARG]

required arguments:
  --required_arg REQUIRED_ARG

optional arguments:
  -h, --help                    show this help message and exit
  --optional_arg OPTIONAL_ARG