input: 
  def swap(arr1, arr2):
      """
      Swap the elements of two given arrays of integers. Both arrays should be the same length.
      >>> swap([3, 5, 6, 9], [2, 4, 7, 8])
      [2, 4, 7, 8]
      >>> swap([1, 2, 3], [4, 5, 6])
      [4, 5, 6]
      """
      assert len(arr1) == len(arr2)
      for i in range(len(arr1)):
          temp = arr1[i]
          arr1[i] = arr2[i]
          arr2[i] = temp
  
output:     return arr1