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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def add_edge(self, graph_edge):
 """Adds an edge object to the graph. It takes a edge object as its only argument and returns None. """


        if not isinstance(graph_edge, Edge):
            raise TypeError('add_edge() received a non edge class object: ' + str(graph_edge))

        edge_points = ( graph_edge.get_source(), graph_edge.get_destination() )

        if self.obj_dict['edges'].has_key(edge_points):

            edge_list = self.obj_dict['edges'][edge_points]
            edge_list.append(graph_edge.obj_dict)

        else:

            self.obj_dict['edges'][edge_points] = [ graph_edge.obj_dict ]


        graph_edge.set_sequence( self.get_next_sequence_number() )

        graph_edge.set_parent_graph( self.get_parent_graph() )