code: def _get_sd(file_descr):
          
          for stream_descr in NonBlockingStreamReader._streams:
              if file_descr == stream_descr.stream.fileno():
                  return stream_descr
          return None
docs: Get streamdescriptor matching file_descr fileno.
  
          :param file_descr: file object
          :return: StreamDescriptor or None