input: Write a function to construct a nested loop in Python to print out the elements of the given input arrays in a new line.
  for x in [1,2,3]:
    for y in [4,5,6]:
        for z in [7,8,9]:
            print(x,y,z)
  assert print_nested_elements([1,2,3], [4,5,6], [7,8,9])==None
  
  # The function does not return a value but prints out the elements as required.
output: def print_nested_elements(arr1, arr2, arr3):
      for x in arr1:
          for y in arr2:
              for z in arr3:
                  print(x, y, z)