input: Write a python function to compute the sum of the items of a given list.
  assert list_sum([3, 5, 6, 10]) == 24
  assert list_sum([1, 2, 3, 4, 5]) == 15
  assert list_sum([0, 0, 0, 0]) == 0
output: def list_sum(lst):
      return sum(lst)