code: def get_command_line_key_for_unknown_config_file_setting(self, key):
          
          key_without_prefix_chars = key.strip(self.prefix_chars)
          command_line_key = self.prefix_chars[0]*2 + key_without_prefix_chars
  
          return command_line_key
docs: Compute a commandline arg key to be used for a config file setting
          that doesn't correspond to any defined configargparse arg (and so
          doesn't have a user-specified commandline arg key).
  
          Args:
              key: The config file key that was being set.