input: Write a function to calculate the sum of all items in a given list. If the list is empty, the function should return 0.
  
  def sum_list(input_list):
    sum = 0
    for i in input_list:
      sum += i
    return sum
  
  assert sum_list([1, 2, 3, 4, 5]) == 15
  assert sum_list([10, 20, 30]) == 60
  assert sum_list([-1, 0, 1]) == 0
  assert sum_list([]) == 0
output: def sum_list(input_list):
    sum = 0
    for i in input_list:
      sum += i
    return sum