code: def _update_classmethod(self, oldcm, newcm):
          
          # While we can't modify the classmethod object itself (it has no
          # mutable attributes), we *can* extract the underlying function
          # (by calling __get__(), which returns a method object) and update
          # it in-place.  We don't have the class available to pass to
          # __get__() but any object except None will do.
          self._update(None, None, oldcm.__get__(0), newcm.__get__(0))
docs: Update a classmethod update.