input: Write a function to compute the sum of the items in a given list. If the list is empty, return 0.
  assert sum_list([1, 2, 3, 4, 5]) == 15
  assert sum_list([10, 20, 30]) == 60
  assert sum_list([-1, -2, -3]) == -6
  assert sum_list([]) == 0
output: def sum_list(lst):
      if not lst:
          return 0
      return sum(lst)