input: Write a python function to sort a list of tuples by the second element in each tuple.
  assert sort_list_of_tuples([(1, 3), (4, 2), (2, 1)])==[(2, 1), (4, 2), (1, 3)]
  assert sort_list_of_tuples([(5, 5), (1, 1), (3, 3)])==[(1, 1), (3, 3), (5, 5)]
  assert sort_list_of_tuples([(1, 2), (2, 1), (3, 3), (4, 0)])==[(4, 0), (2, 1), (1, 2), (3, 3)]
output: def sort_list_of_tuples(lst):
      return sorted(lst, key=lambda x: x[1])