def __repr__(self):
        return "<Requirement(package={package}, version='{version}')>".format(
            package=self.package, version=self.version)
def deserialize(self, value):
        value = decode(value).strip()
        validators.validate_required(value, self._required)
        if not value:
            return None
        validators.validate_choice(value, self._choices)
        return value