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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 unshift(self, chunk):
 """ Pushes a chunk of data back into the internal buffer. This is useful in certain situations where a stream is being consumed by code that needs to "un-consume" some amount of data that it has optimistically pulled out of the source, so that the data can be passed on to some other party. """

        if chunk:
            self._pos -= len(chunk)
            self._unconsumed.append(chunk)