argparse for PowerShell: case insensitive option handling

pwshparse.py

# Drop in replacement for argparse for PowerShell/pwsh argument handling compatibility
# - argparse already supports abbreviated matches
# - ADD: support for case insensitive options
# - ADD: support for automated -Help -? and -Verbose flags

from argparse import ArgumentParser as _ArgumentParser
from argparse import SUPPRESS
from sys import exit
from collections.abc import MutableMapping

try:
    _cmp = str.casefold # support starting in python 3.3
except:
    _cmp = str.lower


class CaseInsensitiveDict(MutableMapping):
    """A minimal implementation of a case insensitive dict.

    Implementation requires string keys, but supports arbitrary values.
    """
    def __init__(self, *args, **kwargs):
        self.__d = dict()
        for k, v in dict(*args, **kwargs).items():
            self[k] = v
    def __getitem__(self, k):
        # print('get', k)
        # print(self.__d)
        return self.__d[_cmp(k)]
    def __setitem__(self, k, v):
        # print('set', k, v)
        self.__d[_cmp(k)] = v
    def __delitem__(self, k):
        return self.__d.__delitem__(k)
    def __iter__(self):
        return iter(self.__d)
    def __len__(self):
        return len(self.__d)
    def __str__(self):
        return self.__d.__str__()

class ArgumentParser(_ArgumentParser):
    """Case insenstive option parser.

    Extend the built-in python argparse.ArgumentParser to add PowerShell
    features, including:

    - Case insensitive option matching
    - Use of -Help, -? for command usage help
    - Adds common options: -Verbose, -Version, -Quiet
    - Allows automated handling of -Version via the "version" kwarg
    """
    def __init__(self, *args, **kwargs):
        # kwargs['add_help'] = False
        prefix = kwargs.get('prefix_chars', '-')[0]
        defaults = kwargs.pop('add_defaults', True)
        self.ver = kwargs.pop('version')
        super().__init__(*args, **kwargs)

        self._option_string_actions = CaseInsensitiveDict(self._option_string_actions)

        if kwargs.get('add_help', True):
            _help = self._option_string_actions[prefix+'h']
            # remove the default -h --help
            del self._option_string_actions[prefix + 'h']
            del self._option_string_actions[prefix*2 + 'help']
            helps = ['-Help', '-?'] # map to PowerShell defaults
            for _hopt in helps:
                self._option_string_actions[_hopt] = _help
            _help.option_strings = helps

        if self.ver:
            self.add_argument(prefix+'Version', action='store_true',
                              help='Display the version information and exit')

        if defaults:
            self.add_argument(prefix+'Verbose', action='count', default=0,
                              help='Display additional runtime information')
            self.add_argument(prefix+'Quiet', action='store_true',
                              help='Display no information, including errors. Overrides, -Verbose')

    def add_argument(self, *args, **kwargs):
        ret = super().add_argument(*args, **kwargs)
        # Add our option strings to our case insensitive dict
        for option_string in ret.option_strings:
            self._option_string_actions[option_string] = ret
        return ret

    def parse_args(self, *args, **kwargs):
        ret = super().parse_args(*args, **kwargs)
        if ret.Version:
            print(self.ver)
            exit(0)
        return ret