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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_contents(self, stream, progress_callback=None):
 """Save contents of stream to part of file instance. If a the MultipartObject is completed this methods raises an ``MultipartAlreadyCompleted`` exception. :param stream: File-like stream. :param size: Size of stream if known. :param chunk_size: Desired chunk size to read stream in. It is up to the storage interface if it respects this value. """

        size, checksum = self.multipart.file.update_contents(
            stream, seek=self.start_byte, size=self.part_size,
            progress_callback=progress_callback,
        )
        self.checksum = checksum
        return self