input: Write a function to swap two numbers without using a temporary variable.
  assert swap_without_variable(3, 5) == (5, 3)
  assert swap_without_variable(10, 20) == (20, 10)
  assert swap_without_variable(0, -1) == (-1, 0)
output: def swap_without_variable(a, b):
      a, b = b, a
      return a, b