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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 trigger_all_callbacks(self, callbacks=None):
 """Trigger callbacks for all keys on all or a subset of subscribers. :param Iterable callbacks: list of callbacks or none for all subscribed :rtype: Iterable[tornado.concurrent.Future] """

        return [ret
                for key in self
                for ret in self.trigger_callbacks(key, callbacks=None)]