如何在argparse互斥组中包含一个位置参数? [英] How to include one positional argument into argparse mutually exclusive group?

问题描述

我知道在一个互斥的组中使用多个位置参数是没有意义的，因为您不能说谁是谁.但是我需要在其中加入一个位置参数.

I know that does not make sense multiple positional arguments into a mutually exclusive group because you can't say who is who. But I need to include ONE positional argument into that.

我需要什么:

$ myprogram -h
usage: myprogram [-h] [--delete value | --update value | value]

其中位置value是默认操作(种类为"--include"). (没有参数的myprogram也必须是有效的.)

Where positional value is the default action (kind of "--include"). (myprogram without arguments must be valid too).

我的第一次尝试(无效):

My first attempt (this doesn't works):

parser = ArgumentParser()
group = parser.add_mutually_exclusive_group()
group.add_argument('--delete', metavar='value')
group.add_argument('--update', metavar='value')
group.add_argument('value')

有可能吗?

第二次尝试:

parser = ArgumentParser()
group = parser.add_mutually_exclusive_group()
group.add_argument('--delete', action='store_true')
group.add_argument('--update', action='store_true')
group.add_argument('--insert', action='store_true', default=True)
group.add_argument('value')

推荐答案

我会做一些不同的事情:

I'd do this a little bit differently:

parser = ArgumentParser()
group = parser.add_mutually_exclusive_group()
group.set_defaults(mode='insert')
group.add_argument('--delete', action='store_const', dest='mode', const='delete')
group.add_argument('--update', action='store_const', dest='mode', const='update')
group.add_argument('--insert', action='store_const', dest='mode', const='insert')
parser.add_argument('value', nargs='?')
args = parser.parse_args()

如果您还想使program --delete(没有value选项)失败，请添加

If you additionally want to make program --delete (with no value option) fail, add

if args.mode != 'insert' and args.value:
    parser.error("can't {} without a value argument".format(args.mode))

请注意，这将意味着program --insert(无value)仍然有效.您可以通过将默认值mode设置为None，使用args.mode is not None进行上述检查，然后再进行if args.mode is None: args.mode = 'insert'或类似的操作来避免这种情况.

Note that this will mean that program --insert (with no value) still works. You could avoid this with a little more effort by having the default mode be None, doing the check above with args.mode is not None, and then doing if args.mode is None: args.mode = 'insert' or similar.

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