>>> import dis >>> def foo(a, b): ... a, b = b, a ... >>> dis.dis(foo) 2 0 LOAD_FAST 1 (b) 3 LOAD_FAST 0 (a) 6 ROT_TWO 7 STORE_FAST 0 (a) 10 STORE_FAST 1 (b) 13 LOAD_CONST 0 (None) 16 RETURN_VALUE