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_bad_input():
    cases = (
        'abc',
        '123abc',
        'abc123',
        '',
    )

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

    for value in cases:
        yield assert_raises, ValueError, lambda: num_only(value)