On Sat, 6 Mar 2021 at 10:42, Vincent Cheong
I see.
You have coined the term exactly, partial-reverse. Nice. You have also put forward a realistic question of 'why do we need'. Well, surely not everyone needs it and definitely it's not urgently needed, but its just the counterintuitive incompleteness such that 'it works for a whole, but not part of it', you see. About the gain, of course it's unlike a monumental speed boost, but its just a little spot that I saw lacking in power.
What I had in mind was the algorithmic cost to the program itself, not the cost in developing it. But now that you explained to me, I understand the situation.
Thanks for the information.
To put this in context, I think that if you were to create a PR for Python, implementing this change, and post it as a feature request to bugs.python.org, it may well be accepted without (much) debate. It's a classic case of "actions speak louder than words", basically - it's fairly easy for a core dev to look at a PR, think "yes, this is a simple and logical enhancement" and focus on tidying up any technical details before simply merging it. Whereas coming to a discussion forum like this one, and opening with (in effect) "it would be nice if someone did X" tends to get everyone thinking about what it would need to persuade them to spend time writing that code, what they'd think about when writing it, etc, etc. And what you get is a long discussion, but little actual action. Paul