Private constructor for direct construction
        of an ObjectGraph from its attributes.

        vertices is the collection of vertices
        out_edges and in_edges map vertices to lists of edges
        head and tail map edges to objects.

def _raw(cls, vertices, edges, out_edges, in_edges, head, tail):
        """
        Private constructor for direct construction
        of an ObjectGraph from its attributes.

        vertices is the collection of vertices
        out_edges and in_edges map vertices to lists of edges
        head and tail map edges to objects.

        """
        self = object.__new__(cls)
        self._out_edges = out_edges
        self._in_edges = in_edges
        self._head = head
        self._tail = tail
        self._vertices = vertices
        self._edges = edges
        return self