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 delete_snapshot(self, snapshot_id):
        """Delete Snapshot."""
        return self.delete("snapshots/%s" % str(snapshot_id))