def clean_semver(cls, version_spec):
        return re.sub(r"([<>=~])\s+?v?", "\\1", version_spec, re.IGNORECASE)
def __init__(
        self, minimum=None, maximum=None, choices=None, optional=False
    ):
        self._required = not optional
        self._minimum = minimum
        self._maximum = maximum
        self._choices = choices