>>> def f():
...  a = 1
...  b = 2
...  a, b = b, a
...
>>> import dis
>>> dis.dis(f)
  2           0 LOAD_CONST               1 (1)
              3 STORE_FAST               0 (a)

  3           6 LOAD_CONST               2 (2)
              9 STORE_FAST               1 (b)

  4          12 LOAD_FAST                1 (b)
             15 LOAD_FAST                0 (a)
             18 ROT_TWO
             19 STORE_FAST               0 (a)
             22 STORE_FAST               1 (b)
             25 LOAD_CONST               0 (None)
             28 RETURN_VALUE