Message 331405 - Python tracker

> Any ideas? Or I will create a PR in a week without 'CPython implementation detail'

I don't think we want to give any stability guarantees for this. Perhaps 
we should explicitly state that this is not guaranteed behaviour and may 
change in the future.

I would be happy for it to be stated as an CPython implementation 
detail. If PyPy or any other implementation happen to duplicate it, 
we're not responsible for documenting that fact.

Please go ahead and make a PR.