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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 associated_stream(self):
 """Return the corresponding output or storage stream for an important system input. Certain system inputs are designed as important and automatically copied to output streams without requiring any manual interaction. This method returns the corresponding stream for an important system input. It will raise an InternalError unlesss the self.important property is True. Returns: DataStream: The corresponding output or storage stream. Raises: InternalError: If this stream is not marked as an important system input. """


        if not self.important:
            raise InternalError("You may only call autocopied_stream on when DataStream.important is True", stream=self)

        if self.stream_id >= DataStream.ImportantSystemStorageStart:
            stream_type = DataStream.BufferedType
        else:
            stream_type = DataStream.OutputType

        return DataStream(stream_type, self.stream_id, True)