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[Python-Dev] GeneratorExit inheriting from Exception

Nick Coghlan ncoghlan at gmail.com
Sun Mar 26 04:59:29 CEST 2006 
Guido van Rossum wrote:
> On 3/25/06, Nick Coghlan <ncoghlan at gmail.com> wrote:
>> The kind of code I'm talking about would be an *existing* Python 2.4 generator
>> that happens to do something like:
>>
>>    def gen(tasks):
>>        """yield the results of a bunch of task functions"""
>>        for task in tasks:
>>            try:
>>                yield (task, task())
>>            except Exception, ex:
>>                yield ExceptionOccurred(task, ex)
> 
> This is purely hypothetical. It doesn't look like good style at all.
> 
>> If you run such a generator on Python 2.5, but don't run it to completion
>> before it is garbage collected, you will get an error message printed on
>> stderr saying that an exception was ignored when this generator was cleaned
>> up. If you use the new PEP 342 features to try to explicitly close it before
>> it is garbage collected, you'll get the exception directly.
> 
> I think this is fine. The code breaks with the new yield semantics.
> But that's because the except clause was overly broad. It's easy to
> rewrite it like this, which is better style anyway because the scope
> of the try/except is limited.
> 
>   try:
>     value = (task, task())
>   except Exception, ex:
>     value = ExceptionOccurred(task, ex)
>   yield value

Works for me. Consider the issue dropped :)

Cheers,
Nick.

-- 
Nick Coghlan   |   ncoghlan at gmail.com   |   Brisbane, Australia
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