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