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    <p>The right thing to do is to allow your <code>Graph</code> class to take a user-defined class as an argument, and use that to represent vertices. Your <code>graph</code> module can provide a suitable default.</p> <p>In <code>graph.py</code> (modules should begin with lowercase letters):</p> <pre><code>class Vertex(object): def __init__(self,key): self.id = key self.connectedTo = {} class Graph(object): def __init__(self, vertexclass=Vertex): self.vertList = {} self.numVertices = 0 self.vertexclass = vertexclass def addVertex(self,key): self.numVertices += 1 newVert = self.vertexclass(key) self.vertList[key] = newVert return newVert def getVertex(self,k): if k in self.vertList: return self.vertList[k] else: return None </code></pre> <p>The only change is that <code>Graph.__init__</code> has a parameter whose default value is the plain <code>Vertex</code> class, allowing you to pass a different class when you create the <code>Graph</code> instance. That class is saved, and you use that whenever <code>addVertex</code> is called to create a new vertex.</p> <p>Then, in another module or script where you want to use a custom vertex class:</p> <pre><code>#!/usr/bin/python import graph class MyVertex(graph.Vertex): def __init__(self,key): super(Vertex,self).__init__(key) # extensions for BFS self.predecessor = None self.dist = 0 self.color = 'w' # white, grey, and black class BFSGraph(Graph): def __init__(self): super(BFSGraph, self).__init__(MyVertex) def getColor(self,k): return self.getVertex(k).color def test(): g=BFSGraph() g.addVertex('a') g.getColor('a') </code></pre> <p>Your <code>BFSGraph.__init__</code>, when called, just calls its parent's <code>__init__</code> with the <code>graph.Vertex</code> subclass you want to use.</p> <p>This is not the only way to organize the code, but the key to remember is that your <code>Graph</code> class (or any subclass derived from it) should document exactly the behavior the class implementing the vertex needs to implement.</p>
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    1. POHow do I use a new extended class instead of the original in another loaded class
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    1. POHow do I use a new extended class instead of the original in another loaded class
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    1. COI ended up renaming the new Vertex as BFSVertex and overriding addVertex in BFSGraph to explicitly use BFSVertex. Thanks for the tips guys!
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      1. USAlexander Tronchin-James
 

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