code: def _pfp__handle_updated(self, watched_field):
          
          self._pfp__no_notify = True
  
          # nested data has been changed, so rebuild the
          # nested data to update the field
          # TODO a global setting to determine this behavior?
          # could slow things down a bit for large nested structures
  
          # notice the use of _is_ here - 'is' != '=='. '==' uses
          # the __eq__ operator, while is compares id(object) results
          if watched_field is self._:
              self._pfp__pack_data()
          elif self._pfp__update_func is not None:
              self._pfp__update_func.call(
                  [self] + self._pfp__watch_fields,
                  *self._pfp__update_func_call_info
              )
  
          self._pfp__no_notify = False
docs: Handle the watched field that was updated