def __missing__(self, key):
        if self.default_factory is None:
            raise KeyError(key)
        else:
            ret = self[key] = self.default_factory(name=key)
            return ret
def test_regex_good_input():
    cases = (
        '123',
        '1234567890',
        '00000',
    )

    num_only = inputs.regex(r'^[0-9]+$')

    for value in cases:
        yield assert_equal, num_only(value), value