input: Write a python function to calculate the sum of all elements in a list.
  assert sum_of_list([1, 2, 3, 4, 5]) == 15
  assert sum_of_list([10, 20, 30, 40]) == 100
  assert sum_of_list([7, 14, 21, 28, 35]) == 105
output: def sum_of_list(lst):
      return sum(lst)