>>> a = 275638
>>> b = 362553
>>> a,b
(275638, 362553)
>>> a ^= b
>>> a,b
(113807, 362553)
>>> b ^= a
>>> a,b
(113807, 275638)
>>> a ^= b
>>> a,b
(362553, 275638)

a,b以外の変数を使わずに値を入れ替えるときの常套手段