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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def _comm_changed(self, change):
 """Called when the comm is changed."""

        if change['new'] is None:
            return
        self._model_id = self.model_id

        self.comm.on_msg(self._handle_msg)
        Widget.widgets[self.model_id] = self