Under the hood

The graph has:

• _vertexlist a list of all vertices have a back reference in order of addition
• _vertexdict a dictionary of all vertices indexed by name
• _edgelist a list of all edges

Every vertex has:

• coord the coordinate of the vertex if the graph is embedded
• _edgelist a list of all edges starting at this vertex. For an undirected graph this is all edges, for a directed graph this is all edges leaving this vertex
• name a unique name, if not given a name of the form #N is given where N is the index of the vertex in the graph's _vertexlist
• a back reference to its owning graph which is set when the vertex is added to the graph by add_vertex. This means a vertex can only be in one graph.

Every edge has:

• a reference to the vertices which are its endpoints
• cost which is the cost of traversing the edge
• data which is a reference to arbitrary user data associated with the edge. A more general approach is to subclass Edge.

The key objects and their interactions are shown below.