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