input: Write a function to compute the sum of all elements in a given list. If the input list is empty, return 0.
  assert sum_list([1, 2, 3, 4, 5]) == 15
  assert sum_list([]) == 0
  assert sum_list([10, -3, 7]) == 14
output: def sum_list(lst):
      if not lst:
          return 0
      return sum(lst)