.

allgraphs.py

 #!/usr/bin/env python
 """generate all connected graphs up to N nodes"""
 
-from __future__ import print_statement
+from __future__ import print_function
+import sys
 
 
 class Graph:
     # .nodes    {nodes}
     # .edges    {edges}
 
-    def __init__(nodes, edges):
-        self.nodes = set(nodes)
-        self.edges = set(edges)
+    def __init__(g, nodes, edges):
+        g.nodes = set(nodes)
+        g.edges = set(edges)
 
-    def __str__(self):
-        return "Graph nodes=%s  edges=%s" % (self.nodes, self.edges)
+    def __str__(g):
+        return "Graph nodes=%s  edges=%s" % (g.nodes, g.edges)
 
 
 # generate all connected graphs with N(nodes) =< N
@@ -23,8 +24,8 @@ def genGraphs(N):
     nodes  = []         # of all nodes
     Sprevedges = set()  # set of edges for all graphs with (i-1) nodes
 
-    for i in range(N):
-        n = ('r' if i == 0 else 'n%d' % i)
+    for i in range(1,N+1):
+        n = ('r' if i == 1 else 'n%d' % (i-1))
         nodes = nodes + [n]
         Sedges = set()
 
@@ -32,7 +33,7 @@ def genGraphs(N):
         # is connected to at least one node in the previous graph.
 
         # for all combinations to which nodes n is connected in the previous graph.
-        for j in range(1,2**(i-1)):
+        for j in range(1, 1<<(i-1)):
             Snewconn = set()
             for k in range(i-1):
                 if j & (1 << k):
@@ -42,7 +43,7 @@ def genGraphs(N):
                 for newconn in Snewconn:
                     newedges = edges.union(newconn)
                     Sedges.add(newedges)
-                    yield Graph(node, newedges)
+                    yield Graph(nodes, newedges)
 
         Sprevedges = Sedges