input: 
  def swap(arr1: List[int], arr2: List[int]):
      """
      Swap elements between two arrays of integers.
      >>> swap([3, 5, 6, 9], [2, 4, 7, 8])
      >>> [3, 5, 6, 9] == [2, 4, 7, 8] and [2, 4, 7, 8] == [3, 5, 6, 9]
      True
      >>> swap([1, 2, 3], [4, 5, 6])
      >>> [1, 2, 3] == [4, 5, 6] and [4, 5, 6] == [1, 2, 3]
      True
      """
      assert len(arr1) == len(arr2)
      for i in range(len(arr1)):
          temp = arr1[i]
          arr1[i] = arr2[i]
          arr2[i] = temp
  
output:     assert len(arr1) == len(arr2)
      for i in range(len(arr1)):
          temp = arr1[i]
          arr1[i] = arr2[i]
          arr2[i] = temp