code: def save(self, filename=None):
          
          if self.__fname is None and filename is None:
              raise ValueError('Config loaded from string, no filename specified')
          conf = self.__config
          cpa = dict_to_cp(conf)
          with open(self.__fname if filename is None else filename, 'w') as f:
              cpa.write(f)
docs: Write config to file.