'takes kwargs that were passed to a command\'s __call__ and extracts
out the special keyword arguments, we return a tuple of special keyword
args, and kwargs that will go to the execd command'

@staticmethod
def _extract_call_args(kwargs):

    kwargs = kwargs.copy()
    call_args = {}
    for (parg, default) in Command._call_args.items():
        key = ('_' + parg)
        if (key in kwargs):
            call_args[parg] = kwargs[key]
            del kwargs[key]
    invalid_kwargs = special_kwarg_validator(call_args, Command._kwarg_validators)
    if invalid_kwargs:
        exc_msg = []
        for (args, error_msg) in invalid_kwargs:
            exc_msg.append(('        %r:    %s' % (args, error_msg)))
        exc_msg = '\n'.join(exc_msg)
        raise TypeError(('Invalid    special    arguments:\n\n%s\n' % exc_msg))
    return (call_args, kwargs)
