9.3. The Graph Abstract Data Type¶
The graph abstract data type (ADT) is defined as follows:
Graph()creates a new, empty graph.
addVertex(vert)adds an instance of
Vertexto the graph.
addEdge(fromVert, toVert)Adds a new, directed edge to the graph that connects two vertices.
addEdge(fromVert, toVert, weight)Adds a new, weighted, directed edge to the graph that connects two vertices.
getVertex(vertKey)finds the vertex in the graph named
getVertices()returns the list of all vertices in the graph.
Truefor a statement of the form
vertex in graph, if the given vertex is in the graph,
Beginning with the formal definition for a graph there are several ways we can implement the graph ADT in Python. We will see that there are trade-offs in using different representations to implement the ADT described above. There are two well-known implementations of a graph, the adjacency matrix and the adjacency list. We will explain both of these options, and then implement one as a Python class.