def __str__(self):
        return "\n".join([str(x) for x in self])
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)