Rather than

    self.sock = None

I would do

    self.sock.close()

which should work better for non-refcounted Pythons.

Of course it would be better to do this immediately after forking (i.e. before any more fds are created), otherwise you could still accidentally zap the fd of some other object.

If you can't do this immediately after forking then maybe it is better to move inherited potentially broken objects to a garbage list to prevent garbage collection.