python-patterns/graph_search.py

class GraphSearch:
    """Graph search emulation in python, from source
    http://www.python.org/doc/essays/graphs/"""

    def __init__(self, graph):
        self.graph = graph 
    
    def find_path(self, start, end, path=[]):
        self.start = start
        self.end = end
        self.path = path

        self.path += [self.start]
        if self.start == self.end:
            return self.path
        if not self.graph.has_key(self.start):
            return None
        for node in self.graph[self.start]:
            if node not in self.path:
                newpath = self.find_path(node, self.end, self.path)
                if newpath:
                    return newpath
        return None

    def find_all_path(self, start, end, path=[]):            
        self.start = start
        self.end = end
        self.path = path
        self.path += [self.start]
        if self.start == self.end:
            return [self.path]
        if not self.graph.has_key(self.start):
            return []
        paths = []
        for node in self.graph[self.start]:
            if node not in self.path:
                newpaths = self.find_all_path(node, self.end, self.path)
                for newpath in newpaths:
                    paths.append(newpath)                
        return paths

    def find_shortest_path(self, start, end, path=[]):         
        self.start = start
        self.end = end
        self.path = path
        
        self.path += [self.start]
        if self.start == self.end:
            return self.path
        if not self.graph.has_key(self.start):
            return None
        shortest = None
        for node in self.graph[self.start]:
            if node not in self.path:
                newpath = self.find_shortest_path(node, self.end, self.path)
                if newpath:
                    if not shortest or len(newpath) < len(shortest):
                        shortest = newpath
        return shortest

#example of graph usage
graph = {'A': ['B', 'C'],
         'B': ['C', 'D'],
         'C': ['D'],
         'D': ['C'],
         'E': ['F'],
         'F': ['C']   
         }

#initialization of new graph search object
graph1 = GraphSearch(graph)


print graph1.find_path('A', 'D')
print graph1.find_all_path('A', 'D')
print graph1.find_shortest_path('A', 'D')