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 _getProvenance(self, item, user, version=None, resource='item',
                       checkOk=True):
        params = {}
        if version is not None:
            params = {'version': version}
        resp = self.request(
            path='/%s/%s/provenance' % (resource, item['_id']),
            method='GET', user=user, type='application/json', params=params)
        if checkOk:
            self.assertStatusOk(resp)
        return resp