Python default matching decorator and default value retrieval function

gistfile1.py

class matchdefaults(object):
    """
    This decorator swaps out the decorated function's default values to the
    `match` function. This does not sanity check the number of parameters or
    their names.
    """

    def __init__(self, match):
        self.match = match

    def __call__(self, func):
        func._func_defaults = copy(func.func_defaults)
        func.func_defaults = self.match.func_defaults
        return func


def default_arg(func, argname):
    argnames = inspect.getargspec(func).args
    defaults = func.func_defaults or ()
    arg_defaults = dict(zip(argnames[len(defaults)-1:], defaults))
    return arg_defaults[argname]


def get_default_arg(func, argname, default=None):
    try:
        return default_arg(func, argname)
    except KeyError:
        return default