[Python-Dev] Single- vs. Multi-pass iterability

[Guido van Rossum]

> Well, i guess that's part of the protocol philosophy.  There exist
> cursor-like objects that would be natural candidates for being used
> like iterators (files are one example, database cursors are another).
> Choosing __next__ makes it possible to add support to an existing
> object when appropriate, instead of requiring an auxiliary object
> regardless of whether it's appropriate or inappropriate.

OK, that's clear.

> To me, the former feels like the more typical Python thing to do,
> because it's consistent with the way all the other protocols work.
> So it's from this perspective that "next" without underscores
> is a wart to me.

Yes.

> For example, when something is container-like you can implement
> __getitem__ on the object itself, and then you can use [] with the
> object.  Some objects let you fetch containers and some objects
> implement __getitem__ on their own.  But we don't force everybody
> to provide a convert-to-container operation in all cases before
> allowing them to provide __getitem__.

Correct.

Now, weren't you a co-author of the Iterator PEP?  I wish you'd
brought this up then.  Or maybe you did, and I overruled you.  Sorry
then.

But I don't think we can withdraw this so easily.  It's not the end of
the world.

--Guido van Rossum (home page: http://www.python.org/~guido/)