argparse:使用必需参数的值设置可选参数 [英] argparse: setting optional argument with value of mandatory argument

问题描述

使用Python的 argparse ，我想添加一个可选参数，如果没有给出该参数，另一个(强制性)参数的值.

With Python's argparse, I would like to add an optional argument that, if not given, gets the value of another (mandatory) argument.

parser.add_argument('filename',
                    metavar = 'FILE',
                    type    = str,
                    help    = 'input file'
                    )

parser.add_argument('--extra-file', '-f',
                    metavar = 'ANOTHER_FILE',
                    type    = str,
                    default = ,
                    help    = 'complementary file (default: FILE)'
                    )

我当然可以在解析参数之后手动检查None，但是没有更Python的方式可以做到这一点吗?

I could of course manually check for None after the arguments are parsed, but isn't there a more pythonic way of doing this?

推荐答案

据我所知，没有比这更干净的方法了:

As far as I know, there is no way to do this that is more clean than:

ns = parser.parse_args()
ns.extra_file = ns.extra_file if ns.extra_file else ns.filename

(就像您在问题中提出的一样).

(just like you propose in your question).

您可以可能会做一些与此类似的自定义动作体操，但是我真的不知道认为那是不值得的(或"pythonic").

You could probably do some custom action gymnastics similar to this, but I really don't think that would be worthwhile (or "pythonic").

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