Python argparse可选子参数

问题描述

我想为我的程序提供一个参数，该参数包含一些必需的参数以及一些可选的参数.像这样:

I'd like to have an argument to my program that has some required parameters along with some optional parameters. Something like this:

[--print text [color [size]]

因此您可以通过以下任何一种方式:

so you could pass it any of these:

mycommand --print hello
mycommand --print hello blue
mycommand --print hello red 12

可能有多个，因此必须是一个add_argument.例如:

There could be multiple of these so it has to be a single add_argument. For example:

[--print text [color]] [--output filename [overwrite]]

我可以实现接近我想要的参数:

I can achieve arguments that are close to what I want:

>>> parser = argparse.ArgumentParser()
>>> act = parser.add_argument('--foo', nargs=3, metavar=('x','y','z'))
>>> act = parser.add_argument('--bar', nargs='?')
>>> act = parser.add_argument('--baz', nargs='*')
>>> parser.print_help()
usage: [-h] [--foo x y z] [--bar [BAR]] [--baz [BAZ [BAZ ...]]]

optional arguments:
  -h, --help            show this help message and exit
  --foo x y z
  --bar [BAR]
  --baz [BAZ [BAZ ...]]

但不完全是.有什么办法可以用argparse做到这一点?我知道我可以将它们全部设置为nargs="*"，但是--help不会列出可选参数的名称.如果我通过nargs="*"和metavar的元组，则argparse会引发异常.

but not quite. Is there any way to do this with argparse? I know I could make them all nargs="*" but then --help would not list the names of the optional arguments. If I pass nargs="*" and a tuple for metavar, argparse throws an exception.

推荐答案

阅读源代码(从take_action开始)，我相信您想要的是不可能的.所有参数解析和传递到操作均基于nargs完成，并且nargs是一个数字，OPTIONAL(?")，ZERO_OR_MORE("*")，ONE_OR_MORE("+")，PARSER或REMAINDER.必须在Action对象(处理输入)甚至看到它得到的东西之前确定它，因此它不能动态地找出nargs.

Reading the source code (start in take_action), I believe what you want is impossible. All argument parsing and passing to actions is done based on nargs, and nargs is either a number, OPTIONAL ("?"), ZERO_OR_MORE ("*"), ONE_OR_MORE ("+"), PARSER, or REMAINDER. This must be determined before the Action object (which handles the input) even sees what it's getting, so it can't dynamically figure out nargs.

我认为您将需要一个变通方法.我可能会有--foo-x x，--foo-y y和--foo-z z，也许还有--foo x y z.

I think you'll need to live with a workaround. I would maybe have --foo-x x, --foo-y y, and --foo-z z, and perhaps also --foo x y z.

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