>>> dis(s3f)
2 0 SETUP_LOOP 32 (to 35)
3 LOAD_GLOBAL 0 (enumerate)
6 LOAD_GLOBAL 1 (lst)
9 CALL_FUNCTION 1
12 GET_ITER
>> 13 FOR_ITER 18 (to 34)
16 UNPACK_SEQUENCE 2
19 STORE_FAST 0 (i)
22 STORE_FAST 1 (v)
3 25 LOAD_FAST 1 (v)
28 STORE_FAST 2 (elem)
31 JUMP_ABSOLUTE 13
>> 34 POP_BLOCK
>> 35 LOAD_CONST 0 (None)
38 RETURN_VALUE
>>>