code: def check_keys_split(self, decoded):
          
          bad_keys = set(decoded.keys()).difference(set(self._split_keys))
          if bad_keys:
              bad_keys = ", ".join(bad_keys)
              raise ValueError("JSON data had unexpected key(s): {bad_keys}"
                               .format(bad_keys=pprint_thing(bad_keys)))
docs: Checks that dict has only the appropriate keys for orient='split'.