code: def find_duplicate_keys(data):
      
      out_dict = {}
      for key, value in data:
          if key in out_dict:
              raise ValueError("Duplicate key: {}".format(key))
          out_dict[key] = value
      return out_dict
docs: Find duplicate keys in a layer of ordered pairs. Intended as the object_pairs_hook callable
      for json.load or loads.
  
      :param data: ordered pairs
      :return: Dictionary with no duplicate keys
      :raises ValueError if duplicate keys are found