input: Write a python function to sum the values of all items in a dictionary.
  assert sum_dict_items({'a': 1, 'b': 2, 'c': 3}) == 6
  assert sum_dict_items({'x': 10, 'y': 20, 'z': 30}) == 60
  assert sum_dict_items({'key1': 5, 'key2': 15, 'key3': 25}) == 45
output: def sum_dict_items(d):
      return sum(d.values())