Yep, thanks for the explanation! After some more research into this it appears this exact situation is accounted for within the `SQLAlchemy` library (reference: https://github.com/sqlalchemy/sqlalchemy/issues/5810)! Additionally, due to the complications brought up in this thread it seems like it's probably best to leave `__eq__` as the default implementation.
Thanks for expanding my knowledge and Happy New Year! 🎊 Andres On Thu, Dec 31, 2020 at 4:40 PM Rob Cliffe <rob.cli...@btinternet.com> wrote: > > > You bring up a good point regarding how to determine iterable equality. > For example, with your last example, I had no idea that the same iterable > behavior could produce radically different results between cyclers. To be > quite honest, I don't really understand what causing this quirky behavior. > Assuming that you refer to Steven D'Aprano's example: > > I didn't understand it either until I played with it a bit. If I > remember correctly it started something like this: > > it = iter([1,2,3]) > a = cycle(it) > b = cycle(it) > > Now cycle() reads elements from the iterator until it is exhausted, > meanwhile storing them. Then it cycles through the stored copies. The > problem is that a and b point to the *same* iterator and interfere with > one another. So: > > next(a) # gets 1 from 'it', stores 1, and returns 1 > next(b) # gets 2 from 'it', stores 2, and returns 2 > next(a) # gets 3 from 'it', stores 3, and returns 3 > > Now the iterator is exhausted. So subsequent calls of next(a) will > cycle through a's stored elements, viz. 1 and 3. Subsequent calls of > next (b) will repeat b's only stored element, viz 2. > > If instead we wrote: > > a = cycle(iter([1,2,3])) > b = cycle(iter([1,2,3])) > > then although a and b *don't* refer to the *same iterator*, they *will* > behave identically. > > It seems to me that this makes trying to define "equality" of cycles > problematic. > > Happy New Year > Rob Cliffe > >
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