code: def set_block(fd):
      
      flags = fcntl.fcntl(fd, fcntl.F_GETFL)
      fcntl.fcntl(fd, fcntl.F_SETFL, flags & ~os.O_NONBLOCK)
docs: Inverse of :func:`set_nonblock`, i.e. cause `fd` to block the thread
      when the underlying kernel buffer is exhausted.