如何使用argparse将列表作为命令行参数传递?

问题描述

我正在尝试将列表作为参数传递给命令行程序.是否有 argparse 选项将列表作为选项传递?

I am trying to pass a list as an argument to a command line program. Is there an argparse option to pass a list as option?

parser.add_argument('-l', '--list',
                      type=list, action='store',
                      dest='list',
                      help='<Required> Set flag',
                      required=True)

脚本的调用方式如下

python test.py -l "265340 268738 270774 270817"

推荐答案

TL; DR

使用nargs选项或action选项的'append'设置(取决于用户界面的行为方式).

Use the nargs option or the 'append' setting of the action option (depending on how you want the user interface to behave).

打nar

parser.add_argument('-l','--list', nargs='+', help='<Required> Set flag', required=True)
# Use like:
# python arg.py -l 1234 2345 3456 4567

nargs='+'接受1个或多个参数，nargs='*'接受零个或多个参数.

nargs='+' takes 1 or more arguments, nargs='*' takes zero or more.

追加

parser.add_argument('-l','--list', action='append', help='<Required> Set flag', required=True)
# Use like:
# python arg.py -l 1234 -l 2345 -l 3456 -l 4567

使用append，您可以多次提供选项以建立列表.

With append you provide the option multiple times to build up the list.

请勿使用type=list !!! -可能不会出现将type=list与argparse一起使用的情况.曾经.

Don't use type=list!!! - There is probably no situation where you would want to use type=list with argparse. Ever.

让我们更详细地了解人们可能尝试执行此操作的一些不同方式以及最终结果.

Let's take a look in more detail at some of the different ways one might try to do this, and the end result.

import argparse

parser = argparse.ArgumentParser()

# By default it will fail with multiple arguments.
parser.add_argument('--default')

# Telling the type to be a list will also fail for multiple arguments,
# but give incorrect results for a single argument.
parser.add_argument('--list-type', type=list)

# This will allow you to provide multiple arguments, but you will get
# a list of lists which is not desired.
parser.add_argument('--list-type-nargs', type=list, nargs='+')

# This is the correct way to handle accepting multiple arguments.
# '+' == 1 or more.
# '*' == 0 or more.
# '?' == 0 or 1.
# An int is an explicit number of arguments to accept.
parser.add_argument('--nargs', nargs='+')

# To make the input integers
parser.add_argument('--nargs-int-type', nargs='+', type=int)

# An alternate way to accept multiple inputs, but you must
# provide the flag once per input. Of course, you can use
# type=int here if you want.
parser.add_argument('--append-action', action='append')

# To show the results of the given option to screen.
for _, value in parser.parse_args()._get_kwargs():
    if value is not None:
        print(value)

这是您可以期待的输出:

Here is the output you can expect:

$ python arg.py --default 1234 2345 3456 4567
...
arg.py: error: unrecognized arguments: 2345 3456 4567

$ python arg.py --list-type 1234 2345 3456 4567
...
arg.py: error: unrecognized arguments: 2345 3456 4567

$ # Quotes won't help here...
$ python arg.py --list-type "1234 2345 3456 4567"
['1', '2', '3', '4', ' ', '2', '3', '4', '5', ' ', '3', '4', '5', '6', ' ', '4', '5', '6', '7']

$ python arg.py --list-type-nargs 1234 2345 3456 4567
[['1', '2', '3', '4'], ['2', '3', '4', '5'], ['3', '4', '5', '6'], ['4', '5', '6', '7']]

$ python arg.py --nargs 1234 2345 3456 4567
['1234', '2345', '3456', '4567']

$ python arg.py --nargs-int-type 1234 2345 3456 4567
[1234, 2345, 3456, 4567]

$ # Negative numbers are handled perfectly fine out of the box.
$ python arg.py --nargs-int-type -1234 2345 -3456 4567
[-1234, 2345, -3456, 4567]

$ python arg.py --append-action 1234 --append-action 2345 --append-action 3456 --append-action 4567
['1234', '2345', '3456', '4567']

要点:

• 使用nargs或action='append'
  从用户的角度来看，
  • nargs可能更直接，但是如果存在位置参数则可能不直观，因为argparse不能分辨什么应该是位置参数以及什么属于nargs.如果您有位置参数，那么action='append'可能最终是一个更好的选择.
  • 仅当为nargs指定了'*'，'+'或'?'时，上述情况才成立.如果提供整数(例如4)，则将选项与nargs和位置参数混合不会有问题，因为argparse会确切知道期望该选项有多少个值.
  • Use nargs or action='append'
    • nargs can be more straightforward from a user perspective, but it can be unintuitive if there are positional arguments because argparse can't tell what should be a positional argument and what belongs to the nargs; if you have positional arguments then action='append' may end up being a better choice.
    • The above is only true if nargs is given '*', '+', or '?'. If you provide an integer number (such as 4) then there will be no problem mixing options with nargs and positional arguments because argparse will know exactly how many values to expect for the option.
    • 之所以会发生这种情况，是因为argparse在后台使用type的值来强制每个给定参数您所选择的type，而不是所有参数的总和.
    • 您可以使用type=int(或其他任何方式)获取整数(或其他任何内容)列表
    • This happens because under the hood argparse uses the value of type to coerce each individual given argument you your chosen type, not the aggregate of all arguments.
    • You can use type=int (or whatever) to get a list of ints (or whatever)

    :我一般不是这样..我的意思是您不想使用引号将列表传递给argparse .

    : I don't mean in general.. I mean using quotes to pass a list to argparse is not what you want.

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