code: def _normalize_options(self, options):
          
          for key, value in list(options.items()):
              if '--' in key:
                  normalized_key = self._normalize_arg(key)
              else:
                  normalized_key = '--%s' % self._normalize_arg(key)
  
              if isinstance(value, (list, tuple)):
                  for opt_val in value:
                      yield (normalized_key, opt_val)
              else:
                  yield (normalized_key, str(value) if value else value)
docs: Generator of 2-tuples (option-key, option-value).
          When options spec is a list, generate a 2-tuples per list item.
  
          :param options: dict {option: value}
  
          returns:
            iterator (option-key, option-value)
            - option names lower cased and prepended with
            '--' if necessary. Non-empty values cast to str