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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 _double_prefix(self):
 """Grow the given deque by doubling, but don't split the second chunk just because the first one is small. """

        new_len = max(len(self._buf[0]) * 2, (len(self._buf[0]) + len(self._buf[1])))
        self._merge_prefix(new_len)