code: def extract_variables(log_format):
      
      if log_format == 'combined':
          log_format = LOG_FORMAT_COMBINED
      for match in re.findall(REGEX_LOG_FORMAT_VARIABLE, log_format):
          yield match
docs: Extract all variables from a log format string.
      :param log_format: format string to extract
      :return: iterator over all variables in given format string