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_between():
    """Greater than or equal to y and less than z."""
    p = are.between(3, 4)
    ps = [p(x) for x in range(1, 6)]
    assert ps == [False, False, True, False, False]