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])==None, but output should be: 5 4 3 2 1
  assert print_reverse_array([9, 7, 5, 3, 1])==None, but output should be: 1 3 5 7 9
  assert print_reverse_array(['a', 'b', 'c'])==None, but output should be: c b a
  assert print_reverse_array([])==None, but output should be: (no output since the array is empty)
output: def print_reverse_array(arr):
   for i in range(len(arr)-1, -1, -1): 
    print(arr[i])