def swap(a, b):
    t = a
    a = b
    b = t

  def swap2(a, b):
    t = a['v']
    a['v'] = b['v']
    b['v'] = t

  x = 3
  y = 8
  xx = {'v': x}
  yy = {'v': y}

  swap(x, y) # changes nothing
  swap(xx, yy) # changes nothing
  swap2(xx, yy) # changes 'v' values in xx and yy, but not x or y