input: Write a function to sum up all elements of a list that are divisible by 3. If the input list is empty, return 0.
  def divisibleBy3(li):
   total = 0
   for num in li:
    if num % 3 == 0:
     total += num
   return total
  assert divisibleBy3([4, 6, 17, 24, 5, 9]) == 39
  assert divisibleBy3([0, 3, 6, 9]) == 18
  assert divisibleBy3([]) == 0
  assert divisibleBy3([2, 5, 7, 8]) == 0
  assert divisibleBy3([3]) == 3
  assert divisibleBy3([1, 2, 3, 4, 5, 6]) == 9
output: def divisibleBy3(li):
   total = 0
   for num in li:
    if num % 3 == 0:
     total += num
   return total