python - 互斥参数提示 Action 索引

Question

我正在尝试对参数进行分组，以便用户可以执行以下任一操作:

python sample.py scan -a 1 -b 2
or
python sample.pt save -d /tmp -n something

这是我的代码:

import argparse
if __name__ == '__main__':
    parser = argparse.ArgumentParser(
            description='this is the description'
            )
    parser.add_argument('op', choices=['scan','save'], help='operation', default='scan')
    root_group = parser.add_mutually_exclusive_group()

    group1 = root_group.add_argument_group('g1', 'scan')
    group1.add_argument('-a', help='dir1')
    group1.add_argument('-b', help='dir2')

    group2 = root_group.add_argument_group('g2', 'save')
    group2.add_argument('-d', help='dir')
    group2.add_argument('-n', help='name')

    args = parser.parse_args()
    print args

当我运行 python sample.py --help

我遇到了一个错误。有人可以告诉我如何解决吗？

Traceback (most recent call last):
  File "sample.py", line 18, in <module>
    args = parser.parse_args()
  File "C:\Python27\lib\argparse.py", line 1688, in parse_args
    args, argv = self.parse_known_args(args, namespace)
  File "C:\Python27\lib\argparse.py", line 1720, in parse_known_args
    namespace, args = self._parse_known_args(args, namespace)
  File "C:\Python27\lib\argparse.py", line 1926, in _parse_known_args
    start_index = consume_optional(start_index)
  File "C:\Python27\lib\argparse.py", line 1866, in consume_optional
    take_action(action, args, option_string)
  File "C:\Python27\lib\argparse.py", line 1794, in take_action
    action(self, namespace, argument_values, option_string)
  File "C:\Python27\lib\argparse.py", line 994, in __call__
    parser.print_help()
  File "C:\Python27\lib\argparse.py", line 2313, in print_help
    self._print_message(self.format_help(), file)
  File "C:\Python27\lib\argparse.py", line 2287, in format_help
    return formatter.format_help()
  File "C:\Python27\lib\argparse.py", line 279, in format_help
    help = self._root_section.format_help()
  File "C:\Python27\lib\argparse.py", line 209, in format_help
    func(*args)
  File "C:\Python27\lib\argparse.py", line 317, in _format_usage
    action_usage = format(optionals + positionals, groups)
  File "C:\Python27\lib\argparse.py", line 388, in _format_actions_usage
    start = actions.index(group._group_actions[0])
IndexError: list index out of range

如果我添加 action='store_const'，错误就会消失，并出现一个新的错误，要求 4 个输入。

Answer 1

Argparse 似乎并不完全支持将一个组添加到另一个组中。发生此错误是因为 Argparse 要求 root_group 执行某种操作。解决方法是向组中添加一个参数:

import argparse

if __name__ == '__main__':
    parser = argparse.ArgumentParser(
            description='this is the description'
            )

    # This is now redundant. We can remove it
    # parser.add_argument('op', choices=['scan','save'], help='operation', default='scan')
    root_group = parser.add_mutually_exclusive_group()

    # Workaround
    root_group.add_argument('--scan', help='scan', action='store_true')
    root_group.add_argument('--save', help='save', action='store_true')

    group1 = root_group.add_argument_group('g1', 'scan')
    group2 = root_group.add_argument_group('g2', 'save')

    group1.add_argument('-a', help='dir1')
    group1.add_argument('-b', help='dir2')

    group2.add_argument('-d', help='dir', default='')
    group2.add_argument('-n', help='name')

    args = parser.parse_args()
    print args 

请注意，我们正在使用 --scan 和 --save。要避免使用 -- 前缀，您可能需要 Sub-commands 的帮助。详情可查here .