refactor load/save functions

Use streams instead of filename.
Move load/write functions if modules where logical.

graph.py

@@ -0,0 +1,47 @@
+
+from geometry import x,y
+
+def graph_of( segments ):
+    graph = {}
+    for start,end in segments:
+        graph[start] = graph.get( start, [] )
+        graph[start].append( end )
+        graph[end]   = graph.get( end,   [] )
+        graph[end].append( start )
+    return graph
+
+
+def edges_of( graph ):
+    edges = set()
+    for k in graph:
+        for n in graph[k]:
+            if k != n and (k,n) not in edges and (n,k) not in edges:
+                edges.add( (k,n) )
+    return list(edges)
+
+
+def nodes_of( graph ):
+    return graph.keys()
+
+
+def load( stream ):
+    graph = {}
+    for line in stream:
+        if line.strip()[0] != "#":
+            skey,svals = line.split(":")
+            key = tuple((float(i) for i in skey.split(',')))
+            graph[key] = []
+            for sp in svals.split():
+                p = tuple(float(i) for i in sp.split(","))
+                assert(len(p)==2)
+                graph[key].append( p )
+    return graph
+
+
+def write( graph, stream ):
+    for k in graph:
+        stream.write( "%f,%f:" % (x(k),y(k)) )
+        for p in graph[k]:
+            stream.write( "%f,%f " % (x(p),y(p)) )
+        stream.write("\n")
+