docs: def build_backend(tasks, default_host=('127.0.0.1', DEFAULT_PORT), *args, 
                    **kw):
      """
      Most of these args are passed directly to BackEnd(). However, default_host 
      is used a bit differently. It should be a (host, port) pair, and may be 
      overridden with cmdline args:
        file.py localhost
        file.py localhost 54545
      """
      host, port = default_host
      if len(sys.argv) > 1:
          host = sys.argv[1]
      if len(sys.argv) > 2:
          port = sys.argv[2]
      
      return BackEnd(tasks, host, port, *args, **kw)