code: def add_cmdline_arg(args, arg, *values):
      
      if arg not in args:
          args = list(args) + [arg] + list(values)
      return args
docs: Adds a command line argument *arg* to a list of argument *args*, e.g. as returned from
      :py:func:`global_cmdline_args`. When *arg* exists, *args* is returned unchanged. Otherwise,
      *arg* is appended to the end with optional argument *values*. Example:
  
      .. code-block:: python
  
          args = global_cmdline_values()
          # -> ["--local-scheduler"]
  
          add_cmdline_arg(args, "--local-scheduler")
          # -> ["--local-scheduler"]
  
          add_cmdline_arg(args, "--workers", 4)
          # -> ["--local-scheduler", "--workers", "4"]