input: Write a python function to calculate the sum of all elements except the last one in a list.
  assert sum_except_last([1, 2, 3, 4, 5]) == 10
  assert sum_except_last([10, 20, 30, 40, 50]) == 100
  assert sum_except_last([5, 10, 15, 20]) == 30
output: def sum_except_last(lst):
      return sum(lst[:-1])