input: Write a function to compute the sum of the values of a given dictionary. If the dictionary is empty, return 0.
  
  dict_sum({'A': 5, 'B': 6, 'C': 10}) == 21
  dict_sum({'X': 1, 'Y': 2, 'Z': 3}) == 6
  dict_sum({'P': 7, 'Q': 8, 'R': 9}) == 24
  dict_sum({}) == 0
output: def dict_sum(d):
      return sum(d.values()) if d else 0