OOP question - extending MFace

I’ve been trying to write an extension for the MFace object for a script, but I can’t seem to get access to MFace. I’ve tried

import Blender
from Blender import Mesh
class Mesh(Mesh):
     class MFace(Mesh.MFace): 

but I get an error message saying Mesh has no module called MFace. Am I missing something? I’ve never done classes in Python, so I’m learning on the fly. If anybody could point me towards a script that extends Blender Python classes, I would appreciate it.