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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 filter(self, msg_type=None, maxsize=0):
 """ Get a filtered iterator of messages for synchronous, blocking use in another thread. """

        if self._dead:
            return iter(())
        iterator = Handler._SBPQueueIterator(maxsize)
        # We use a weakref so that the iterator may be garbage collected if it's
        # consumer no longer has a reference.
        ref = weakref.ref(iterator)
        self._sinks.append(ref)

        def feediter(msg, **metadata):
            i = ref()
            if i is not None:
                i(msg, **metadata)
            else:
                raise Handler._DeadCallbackException

        self.add_callback(feediter, msg_type)
        return iterator