code: def add_reader(self, fd, callback):
          " Start watching the file descriptor for read availability. "
          h = msvcrt.get_osfhandle(fd)
          self._read_fds[h] = callbacf add_reader(self, fd, callback):
          " Start watching the file descriptor for read availability. "
          h = msvcrt.get_osfhandle(fd)
          self._read_fds[h] = callback
docs: Start watching the file descriptor for read availability.