[Python-Dev] Termination of two-arg iter()

[Guido van Rossum]

> While agreeing that caution is prudent, this specific reason is a poor one:
> I didn't read the PEP like "a user", but like a standards geek.  It never
> occurred to me that a once-open issue would be resolved *only* in an
> addendum without the resolution also being reflected back into the main
> text.  So I read the main text carefully, but barely even noticed the
> existence of the rest.  On a Bell curve, I expect that way of reading a PEP
> is hugging a tail.

I guess the true meaning of the term "BDFL Pronouncement" hasn't quite
sunk in with you. :-)

> > ...
> > I'd say that *if* there's a useful use of this, we shouldn't break
> > that in the 2.2 branch.  2.3 is a different issue.
> 
> If Marc-Andre hasn't complained yet, there's no use at all for it <wink>.

OK, on to practicalities.

While preparing a patch, I discovered something strange: despite the
fact that listiter_next() never raises StopIteration when it returns
NULL, and despite the fact that it is used as the implementation for
the next() method, calling iter(list()).next() *does* raise
StopIteration, rather than a complaint about NULL without setting an
exception condition.  It took a brief debugging session to discover
that in the presence of a tp_iternext function, the type machinery
adds a next method that wraps tp_iternext.  Cute, though unexpected!
It means that the implementation of various iterators can be a little
simpler, because no next() implementation needs to be given.

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