Raymond Hettinger: "Most of the SETREFs in the next() functions in the itertools module should also be restored to there former state.  They look to have been correct before the change, so there was no improvement, only degradation.  Much of that code had been finely tuned and battle tested over many years -- the addition of SETREFs was gratuitous."

I guess that your concern is performance. Did you notice a performance difference on a micro-benchmark? I don't think that it's possible to see any difference with the addition of a single if in C.

I disagree that the change is gratuitous: it was discussed at length and approved on python-dev and the issue #20440. The idea was not new, it was already proposed in issue #3081 (opened in 2008). The issue #20440 (Py_SETREF) is a generic fix of the bug #16447. PyPy dev found crazy bugs in CPython :-)

IMHO correctness matters more than performance here.

Oh, and by the way, I like a macro which avoids 3 lines of C code ;-) It makes the code shorter and more readable.