def save(self, filename=None):
        filename = Path(filename) if filename is not None else self.filename
        with filename.open("w") as f:
            f.write(self.yaml)
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