input: Write a function to print out an array backwards.
  
  def print_reverse_array(arr):
   for i in range(len(arr)-1, -1, -1): 
    print(arr[i])
  
  assert print_reverse_array([1, 2, 3, 4, 5]) should print out 5 4 3 2 1
  assert print_reverse_array([1]) should print out 1
  assert print_reverse_array([]) should print nothing
  assert print_reverse_array([10, 20, 30]) should print out 30 20 10
output: def print_reverse_array(arr):
   for i in range(len(arr)-1, -1, -1): 
    print(arr[i])