code: def parse(self, argument):
      
      if isinstance(argument, list):
        return argument
      elif not argument:
        return []
      else:
        if self._comma_compat:
          argument = argument.replace(',', ' ')
        return argument.split()
docs: Parses argument as whitespace-separated list of strings.
  
      It also parses argument as comma-separated list of strings if requested.
  
      Args:
        argument: string argument passed in the commandline.
  
      Returns:
        [str], the parsed flag value.