input: Write a function to calculate the sum of all items in a list. If the list is empty, return 0. The function should take a list as input and return the sum of its elements.
  
  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, -2, -3, -4, -5])==-15
  assert sum_list([])==0
output: def sum_list(input_list):
    sum = 0
    for i in input_list:
      sum += i
    return sum