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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 _remove_add_key(self, key):
 """Move a key to the end of the linked list and discard old entries."""

        if not hasattr(self, '_queue'):
            return  # haven't initialized yet, so don't bother
        if key in self._queue:
            self._queue.remove(key)
        self._queue.append(key)
        if self.maxsize == 0:
            return
        while len(self._queue) > self.maxsize:
            del self[self._queue[0]]