On Fri., Oct. 11, 2019, 2:38 a.m. Neil Girdhar, <mistersheik@gmail.com> wrote:

On Fri, Oct 11, 2019 at 2:28 AM Andrew Barnert <abarnert@yahoo.com> wrote:

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On Oct 10, 2019, at 22:13, Neil Girdhar <mistersheik@gmail.com> wrote:

That's funny, I always thought of that as legacy. The iterator protocol has been a special case in so many proposals I've seen on this list. I think it's really ugly. Instead of

collections.abc.OldStyleSequence, what do you think of adding something like InfiniteSequence to collections.abc instead? It's basically Sequence without __len__, __reversed__, or __count__. I don't see it getting much use though.

Are you proposing that this type isn’t allowed to have those methods (as opposed to just not being required to)?

Not required. Just like if we added a row to the table. So, the point of this mixin would be to implement __contains__ __iter__ and __index__ given __getitem__.

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If so that would be a unique ABC, and a pretty weird one. If not, isn’t this exactly equivalent to the original proposal, but just with a different name? And I think it’s a pretty misleading name. Especially if the subclass hook is structural (method-check), because then it would pick up Sequence and Mapping types even though they aren’t infinite sequences. For that matter, not even every useful old-style sequence is infinite; that’s just the most obvious example everyone comes up with first.

Yeah, those are all good points. After sending, I realized, that it would be nicer as a base class of Sequence. I guess I'm for the proposal then. I skipped reading the big debate about structural checks because I think if you really care about this, you should probably either inherit from the ABC or register yourself with it.

Anyway, I guess we pretty much agree then. I just wanted to push against legitimizing the sequence protocol in favor of explicitly inheriting from a mixin (whatever you want to call it, GenericSequence? AbstractSequence? PossiblyInfiniteSequence?) Inheritance like this is a nice declaration of intent. Even if you just implemented __getitem__, I think you would have to have a comment to make the code clear anyway.

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Anyway, I don’t want to put words in Steven’s mouth; maybe this would fit what he wanted. But I suspect it wouldn’t.