code: def get_config_item(cls, key, kb_name, allow_substring=True):
          
          config_dict = cls.kbs.get(kb_name, None)
          if config_dict:
              if key in config_dict:
                  return config_dict[key]
              elif allow_substring:
                  res = [v for k, v in config_dict.items() if key in k]
                  if res:
                      return res[0]
          return key
docs: Return the opposite mapping by searching the imported KB.