Example 1. A complete and usable example

# we have to specify the location of GraphTool
import sys
sys.path.append('/nfs1/etu/info/mait/chuot/ter/cam/graphtool') # please change this

# we import the modules containing the objects we'll extend
import Graph
import Node
import Arc

# the primitives module contains useful functions to interact with the user
import primitives

class MyGraph(Graph.Graph):
    def __init__(self):
        # mandatory call to superclass instance init func
        Graph.Graph.__init__(self)

        # set the node and arc default type
        self._node_type = MyNode
        self._arc_type = MyEdge

        # variable to count nodes
        self.nb_nodes = 0

        # variable to count edges
        self.nb_edges = 0

        # register methods to allow the user read theses values with GraphTool
        self.add_accessor('Number of nodes', self.get_nb_nodes, None)
        self.add_accessor('Number of edges', self.get_nb_edges, None)

    # we intercept the event to take action

    def on_node_creation(self, node):
        self.nb_nodes = self.nb_nodes + 1

    def on_arc_creation(self, arc):
        self.nb_edges = self.nb_edges + 1


    # we now have to write our method to read the values

    def get_nb_nodes(self):
        return self.nb_nodes
    def get_nb_edges(self):
        return self.nb_edges

# we now make our node class (inherits Node of Node module)
class MyNode(Node.Node):
    def __init__(self, graph, name):
        # mandatory
        Node.Node.__init__(self, graph, name)

        # we ask the user to name the node
        self.name = primitives.prompt_user(self._graph._frame, "Enter the node's name")
        
        # we add an accessor to be able to modify this name later
        self.make_default_accessors()
        # this method adds an accessor for each object's variable
        # that does not begin with a '_'

    # when the node is deleted
    def on_delete(self):
        self.graph.nb_nodes = self.nb_nodes - 1
	# we have to return True so that the node will be really deleted
        return True

# and finally our edge class
class MyEdge(Arc.Arc):
    def __init__(self, graph):
        # mandatory
        Arc.Arc.__init__(self, graph)

        # we ask the user to name the arc
        self.name = primitives.prompt_user(self, "Enter the arc's name")

        # and we add the accessor
        self.make_default_accessors()

    def on_delete(self):
        self.graph.nb_edges = self.nb_edges - 1
        return True

# see how it is easy ?