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