如何将一个位置参数包含到 argparse 互斥组中? [英] How to include one positional argument into argparse mutually exclusive group?

问题描述

我知道将多个位置参数放入一个互斥组是没有意义的，因为你不能说谁是谁.但我需要在其中包含一个位置参数.

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]

位置 value 是默认操作(类似于--include").(不带参数的myprogram 也必须有效).

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

我的第一次尝试(这不起作用):

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')

这可能吗?

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

我的做法有点不同:

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()

如果您还想让 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，这意味着 program --insert(没有 value)仍然有效.您可以通过将默认 mode 设置为 None 来避免这种情况，使用 args.mode is not None 进行上述检查，然后做 if args.mode is None: args.mode = 'insert' 或类似的.

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.

这篇关于如何将一个位置参数包含到 argparse 互斥组中?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！