input: Write a function to take as input two arrays of integers and swap their elements. The function should ensure that the two arrays are of equal length before performing the swap.
  
  def swap(arr1, arr2):
      assert len(arr1) == len(arr2)
      for i in range(len(arr1)):
          temp = arr1[i]
          arr1[i] = arr2[i]
          arr2[i] = temp
  
  assert swap([3, 5, 6, 9], [2, 4, 7, 8])==[2, 4, 7, 8]
  assert swap([1, 2, 3], [4, 5, 6])==[4, 5, 6]
  assert swap([], [])==None
  assert swap([10], [20])==[20]
  assert swap([1, 3, 5], [2, 4, 6])==[2, 4, 6]
output: def swap(arr1, arr2):
      if len(arr1) == len(arr2):
          for i in range(len(arr1)):
              temp = arr1[i]
              arr1[i] = arr2[i]
              arr2[i] = temp