refined the PolygonMesh constructor

surf/geometry.py

@@ -133,10 +133,10 @@ class PolygonMesh(object):
       edges, and faces)
     '''
 
-    def __init__(self, *args, **kwargs):
-        self.vertices = [Vertex(*v) for v in kwargs['vertices']]
-        self.edges = kwargs['edges']
-        self.faces = kwargs['faces']
+    def __init__(self, vertices, faces, edges=None, **kwargs):
+        self.vertices = [Vertex(*v) for v in vertices]
+        self.faces = faces
+        self.edges = edges
 
         # the strategy for the following members involves lazy-instantiating
         # them if they weren't passing them in: