input: Write a function to compute the sum of the values of a given dictionary. If the dictionary is empty, return 0.
  assert dict_sum({'A': 5, 'B': 6, 'C': 10}) == 21
  assert dict_sum({'X': 3, 'Y': 8, 'Z': 12}) == 23
  assert dict_sum({}) == 0
output: def dict_sum(d):
      return sum(d.values()) if d else 0