dijkstra in python

dijkstra.py

@@ -0,0 +1,66 @@
+#!/usr/bin/env python
+
+class Infinity:
+    def __eq__(self,other):
+        return isinstance(other,Infinity)
+    def __gt__(self,other):
+        return not isinstance(other, Infinity)
+    def __lt__(self,other):
+        return False
+
+    def __add__(self,other):
+        return self
+    def __radd__(self,other):
+        return self
+
+    def __repr__(self):
+        return "inf"
+
+class Graph:
+    def __init__(self):
+        self.nodes = set()
+        self.edges = set()
+
+    def add_node(self,node):
+        self.nodes.add(node)
+
+    def add_edge(self,nodefrom, nodeto, extra=None):
+        self.edges.add( (nodefrom,nodeto,extra) )
+
+    def all_edges_of(self,nodefrom):
+        return filter(lambda e: e[0] == nodefrom, self.edges)
+
+def dijkstra(graph,startnode):
+    d = { node: Infinity() for node in graph.nodes }
+    d[startnode] = 0
+    V = [startnode]
+
+    while len(V) > 0:
+        node = min(V, key=lambda e: d[e])
+        V.remove(node)
+        for _, neighbor, distance in graph.all_edges_of(node):
+            if d[neighbor] > d[node] + distance:
+                d[neighbor] = d[node] + distance
+                V.append(neighbor)
+
+    return d
+
+def main():
+    g = Graph()
+    for i in range(1,7):
+        g.add_node(i)
+
+    g.add_edge(1,2,10)
+    g.add_edge(1,4,30)
+    g.add_edge(1,5,100)
+    g.add_edge(2,3,50)
+    g.add_edge(3,5,10)
+    g.add_edge(4,3,20)
+    g.add_edge(4,5,60)
+
+    d = dijkstra(g,1)
+
+    print(d)
+
+if __name__ == '__main__':
+    main()