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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 unsubscribe(self, callback_id):
 """Ask the hub to cancel the subscription for callback_id, then delete it from the local database if successful. """

        request = self.get_active_subscription(callback_id)
        request['mode'] = 'unsubscribe'
        self.subscribe_impl(callback_id, **request)