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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 unpack(cls, msg):
 """Construct an _OpReply from raw bytes."""

        # PYTHON-945: ignore starting_from field.
        flags, cursor_id, _, number_returned = cls.UNPACK_FROM(msg)

        # Convert Python 3 memoryview to bytes. Note we should call
        # memoryview.tobytes() if we start using memoryview in Python 2.7.
        documents = bytes(msg[20:])
        return cls(flags, cursor_id, number_returned, documents)