[Python-Dev] Please reconsider PEP 479. (original) (raw)

Isaac Schwabacher ischwabacher at wisc.edu
Mon Nov 24 17:14:18 CET 2014

On 11/23/14, Guido van Rossum wrote:

It wouldn't be so bad if we had the occasional generator author writing "raise StopIteration" instead of "return" to exit from a generator. (We could just add a recommendation against this to the style guide.) But the problem is that an unguarded next() call also raises StopIteration. Sometimes this is intentional (as in some itertools examples). But sometimes an unguarded next() call occurs deep in the bowels of some code called by the generator, and this situation is often hard to debug, since there is no stack track.

I'll admit I've only skimmed the massive volume of correspondence this PEP has generated, but it seems to me that this is the main argument for this change. I can only assume that your support for this PEP is informed by your experience building Tulip, but isn't this the kind of thing that can be accomplished with a warning? Then you can get the same behavior without even needing a future import to protect code bases that expect StopIteration to propagate (which seems like the more elegant and natural thing to do, even if it is more error-prone).

ijs

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