input: Write a function in Python 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]) == None  # backwards: 5 4 3 2 1
  assert print_reverse_array([10, 20, 30]) == None  # backwards: 30 20 10
  assert print_reverse_array([]) == None  # backwards: (nothing printed)
output: def print_reverse_array(arr):
   for i in range(len(arr)-1, -1, -1): 
    print(arr[i])