code: def listen_fds(unset_environment=True):
      
      num = _listen_fds(unset_environment)
      return list(range(LISTEN_FDS_START, LISTEN_FDS_START + num))
docs: Return a list of socket activated descriptors
  
      Example::
  
        (in primary window)
        $ systemd-activate -l 2000 python3 -c \\
            'from systemd.daemon import listen_fds; print(listen_fds())'
        (in another window)
        $ telnet localhost 2000
        (in primary window)
        ...
        Execing python3 (...)
        [3]