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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 _get_sd(file_descr):
 """ Get streamdescriptor matching file_descr fileno. :param file_descr: file object :return: StreamDescriptor or None """

        for stream_descr in NonBlockingStreamReader._streams:
            if file_descr == stream_descr.stream.fileno():
                return stream_descr
        return None