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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 set_body_s(self, stream):
 """Set customized body stream. Note: the body stream can only be changed before the stream is consumed. :param stream: InMemStream/PipeStream for body :except TChannelError: Raise TChannelError if the stream is being sent when you try to change the stream. """

        if self.argstreams[2].state == StreamState.init:
            self.argstreams[2] = stream
        else:
            raise TChannelError(
                "Unable to change the body since the streaming has started")