input: Write a function to swap the values of two variables.
  def swap_variables(x, y):
      x, y = y, x
      return x, y
  
  assert swap_variables(5, 10) == (10, 5)
  assert swap_variables(100, 200) == (200, 100)
  assert swap_variables(-3, 3) == (3, -3)
  assert swap_variables(0, 0) == (0, 0)
  assert swap_variables(-1, 1) == (1, -1)
output: def swap_variables(x, y):
      x, y = y, x
      return x, y