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