[Python-Dev] PEP 479: Change StopIteration handling inside generators (original) (raw)

Donald Stufft donald at stufft.io
Fri Nov 21 17:37:49 CET 2014

On Nov 21, 2014, at 11:31 AM, Ethan Furman <ethan at stoneleaf.us> wrote:

On 11/21/2014 05:47 AM, Raymond Hettinger wrote:

Also, the proposal breaks a reasonably useful pattern of calling next(subiterator) inside a generator and letting the generator terminate when the data stream ends. Here is an example that I have taught for years: def [...] it1 = iter(iterable1) it2 = iter(iterable2) while True: v1 = next(it1) v2 = next(it2) yield v1, v2 Stepping back a little and looking at this code, sans header, let's consider the possible desired behaviors: - have an exact match-up between the two iterators, error otherwise - stop when one is exhausted - pad shorter one to longer one Two of those three possible options are going to require dealing with the StopIteration that shouldn't escape -- is the trade of keeping one option short and simple worth the pain caused by the error-at-a-distance bugs caused when a StopIteration does escape that shouldn't have?

I don’t have an opinion on whether it’s enough of a big deal to actually change it, but I do find wrapping it with a try: except block and returning easier to understand. If you showed me the current code unless I really thought about it I wouldn't think about the fact that the next() calls can cause the generator to terminate.

Donald Stufft PGP: 7C6B 7C5D 5E2B 6356 A926 F04F 6E3C BCE9 3372 DCFA

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