On 2010-08-26, at 6:11 PM, Nick Coghlan wrote: > On Fri, Aug 27, 2010 at 1:00 AM, Yury Selivanov <yseliva...@gmail.com> wrote: >> In the above, GeneratorReturn error will be propagated stopping the program >> execution. >> Strictly speaking, the proposed change is just alters the current Python >> behaviour, >> making the 'return value' statement raise catchable error (instead of >> SyntaxError.) > > There are fairly extensive discussions of using a new GeneratorReturn > exception rather than StopIteration in the python-dev archives. As I > recall, one key factor leading to the use of StopIteration was the > suggestion's implied breakage of the equivalence between "return" > (which would continue to raise StopIteration) and "return None" (which > would raise GeneratorReturn with a value of None). Using a different > exception also made all generator handling code clumsier, since it now > needed to deal with two exceptions rather than just one.
Yes, I understand the point of having two different exceptions for basically two close related things - 'return None' and 'return value'. However, as I outlined in the first message, this was intended to prevent this kind of mistakes: ... def test(): ... for i in range(10): ... yield i ... return 10 Which will certainly happen, especially with people new to python. Again, this exception will be used in very specific places by a very specific software, that expects it. Otherwise, it should be propagated and crash the whole thing. As for the generator handling code -- are you sure there is that much of it? > Since the only situations where a return value could be inadvertently > ignored were those where the application clearly didn't care about the > return value anyway, it was decided that sticking with a single > exception type was the better approach. Good point. It's all about our level of care about beginners ;) > PEP 380 should probably mention this idea explicitly though, since > using a new exception type is a fairly obvious alternative suggestion > and the discussion of the idea is scattered all over the place in the > archives. > > As for breaking the moratorium for it - no, not even close to a big > enough win, since people can already write "raise > CoroutineReturn(result)". Well, people certainly can. But the goal is to make convenient instruments for everyday use. I, for example, deal with really a lot of coroutine based code, and it's very annoying that I have to use some creepy abstractions in order to just return a value! It's especially annoying when you have normal code with normal returns and coroutines, with 'return_ (value)'. And I don't think it frustrates just me. Coroutines protocol is incomplete and there is a very little action required to fix it. All this proposal is suggesting is to replace SyntaxError with GeneratorReturn (or StopIteration). I'd classify is as a minor change than some special refactoring that may fall under the moratorium. Correct me if I'm wrong. - Yury _______________________________________________ Python-Dev mailing list Python-Dev@python.org http://mail.python.org/mailman/listinfo/python-dev Unsubscribe: http://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com
