I left this issue open for three reasons.

1. I had ideas and almost finished patch for different optimization. Unfortunately my hope was not justified, new implementation is slower. If I fail to fix it in few days, I'll close the issue.

2. For bikeshedding in case somebody want to suggest different names or interface.

3. I was going to convert most occurrences of PyArg_ParseTupleAndKeywords() to Argument Clinic for achieving larger effect of this optimization. But this patch was larger than I expected.