input: Write a python function to reverse a list.
  assert reverse_list([1, 2, 3])==[3, 2, 1]
  assert reverse_list([10, 20, 30, 40])==[40, 30, 20, 10]
  assert reverse_list(['a', 'b', 'c'])==['c', 'b', 'a']
output: def reverse_list(lst):
      return lst[::-1]