def __init__(self, groups=None):
        super(GroupedRequirements, self).__init__(NamedRequirements)
        self.groups = groups or self.default_groups
        self.filename = None
        self.create_default_groups()
def update_snapshot(self, snapshot_id, **kwargs):
        """Updates a snapshot."""
        put_body = json.dumps({'snapshot': kwargs})
        resp, body = self.put('snapshots/%s' % snapshot_id, put_body)
        body = json.loads(body)
        return resp, body['snapshot']