[PATCH] py3: catch StopIteration from next() in generatorset

[Sean Farley]

Yuya Nishihara <yuya at tcha.org> writes:

> On Tue, 20 Jun 2017 15:27:56 -0700, Sean Farley wrote:
>> Martin von Zweigbergk <martinvonz at google.com> writes:
>> 
>> > On Tue, Jun 20, 2017 at 2:53 PM, Sean Farley <sean at farley.io> wrote:
>> >> Martin von Zweigbergk via Mercurial-devel
>> >> <mercurial-devel at mercurial-scm.org> writes:
>> >>
>> >>> # HG changeset patch
>> >>> # User Martin von Zweigbergk <martinvonz at google.com>
>> >>> # Date 1497992441 25200
>> >>> #      Tue Jun 20 14:00:41 2017 -0700
>> >>> # Node ID f86d21c457209f5f5a139bcc808be33fbd930424
>> >>> # Parent  0906385672d754f13a512fe70759f0463a069f1e
>> >>> py3: catch StopIteration from next() in generatorset
>> >>>
>> >>> IIUC, letting the StopIteration through would not cause any bugs, but
>> >>> not doing it makes the test-py3-commands.t pass.
>> >>>
>> >>> I have also diligently gone through all uses of next() in our code
>> >>> base. They either:
>> >>>
>> >>>  * are not called from a generator
>> >>>  * pass a default value to next()
>> >>>  * catch StopException
>> >>>  * work on infinite iterators
>> >>>  * request a fixed number of items that matches the generated number
>> >>>  * are about batching in wireproto which I didn't quite follow
>> >>>
>> >>> I'd appreciate if Augie or someone else could take a look at the
>> >>> wireproto batching and convince themselves that the next(batchable)
>> >>> calls there will not raise a StopIteration.
>> >>
>> >> I was just thinking of doing something like this. Shouldn't we just
>> >> 'return None' in Mercurial instead of 'raise StopIteration'?
>> >
>> > I thought "return" was just short for "return None". Are you just
>> > saying that we prefer "return None" in Mercurial? Should I send a v2?
>> 
>> Sorry, no, I was just being sloppy ;-P I meant going through and
>> replacing 'raise StopIteration' with 'return' (e.g. return None) and
>> therefore we shouldn't need to catch StopIteration, correct? Here are
>> the calls I found:
>> 
>> ../mercurial/commandserver.py
>> 142:            raise StopIteration
>> 
>> ../mercurial/manifest.py
>> 124:            raise StopIteration
>> 146:            raise StopIteration
>> 
>> ../mercurial/patch.py
>> 151:                raise StopIteration
>
> IIUC, these StopIteration are valid since they are iterator/generator types.
> On the other hand, generatorset._iterator.gen() is a generator function, which
> should just end (without raising StopIteration) when all items are yielded.

The reason I brought it up is that python3.6 now emits a warning about
'raise StopIteration' being deprecated:

https://www.python.org/dev/peps/pep-0479/

I'll send an RFC series and see what the feedback is.
-------------- next part --------------
A non-text attachment was scrubbed...
Name: signature.asc
Type: application/pgp-signature
Size: 800 bytes
Desc: not available
URL: <http://www.mercurial-scm.org/pipermail/mercurial-devel/attachments/20170621/80174253/attachment.sig>