def METHOD_NAME(self, u, v):
    """Add an edge to graph between nodes ``u`` and ``v``
    ``u`` and ``v`` will be created if they do not already exist.
    """
    # add nodes
    self.add_node(u)
    self.add_node(v)
    # add the edge
    self._succ[u][v] = True
    self._pred[v][u] = True