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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 update(self, incoming_stream, seek=0, size=None, chunk_size=None, progress_callback=None):
 """Update a file in the file system."""

        fp = self.open(mode='r+b')
        try:
            fp.seek(seek)
            bytes_written, checksum = self._write_stream(
                incoming_stream, fp, chunk_size=chunk_size,
                size=size, progress_callback=progress_callback)
        finally:
            fp.close()

        return bytes_written, checksum