def coerce(cls, string):
        """Create a :class:`Requirement` object from a given package spec."""
        match = re.match(cls.spec_regex, string)
        if not match:
            raise InvalidRequirementSpecError("could not parse requirement")
        package = match.group(1)
        if all(match.group(2, 3)):
            version = "".join(match.group(2, 3))
        else:
            version = None
        return cls(package, version)
def encode(self):
        return {
            'af': ip_address(self.gaddr).vapi_af,
            'grp_address': {
                ip_address(self.gaddr).vapi_af_name: self.gaddr
            },
            'src_address': {
                ip_address(self.saddr).vapi_af_name: self.saddr
            },
            'grp_address_length': self.glen,
        }