input: Write a python function to sum all elements in a list.
  assert sum_list([1, 2, 3, 4, 5]) == 15
  assert sum_list([10, 20, 30, 40, 50]) == 150
  assert sum_list([-1, 1, -2, 2, -3, 3]) == 0
output: def sum_list(lst):
      return sum(lst)