带有或不带价值的期权被接受

问题描述：

我有一个小脚本，我需要它能够接受带有值和没有值的参数.

I have a small script and I need it to be able to accept parameter with value and withou value.

./cha.py --pretty-xml
./cha.py --pretty-xml=5

我有这个.

parser.add_argument('--pretty-xml', nargs='?', dest='xml_space', default=4)

但是当我在xml_space中使用--pretty-xml时将为"none".如果我不写此参数，则在xml_space中存储默认值.我需要完全相反.

But when I use --pretty-xml in xml_space will be 'none'. If I dont write this parameter in xml_space is stored the default value. I would need the exact opposite.

答

不使用default参数，而是使用自定义Action:

Leave out the default parameter and use a custom Action instead:

class PrettyXMLAction(argparse.Action):
    def __call__(self, parser, namespace, values, option_string=None):
        if not values:
            values = 4
        setattr(namespace, self.dest, values)

parser.add_argument('--pretty-xml', nargs='?', type=int, dest='xml_space', action=PrettyXMLAction)

演示:

>>> parser = argparse.ArgumentParser()
>>> parser.add_argument('--pretty-xml', nargs='?', type=int, dest='xml_space', action=PrettyXMLAction)
PrettyXMLAction(option_strings=['--pretty-xml'], dest='xml_space', nargs='?', const=None, default=None, type=None, choices=None, help=None, metavar=None)
>>> parser.parse_args('--pretty-xml'.split())
Namespace(xml_space=4)
>>> parser.parse_args('--pretty-xml=5'.split())
Namespace(xml_space=5)
>>> parser.parse_args(''.split())
Namespace(xml_space=None)

带有或不带价值的期权被接受

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