Wednesday, March 28, 2012

Re: Http404 and process_exception

On 29/03/2012, at 12:10 AM, Justin Holmes wrote:

> Russell,
>
> Thanks for the reply.
>
> Two reasons:
>
> 1) Up until now, I hadn't encountered a 404 that had triggered this particular process_exception. It hadn't occurred to me that since get_object_or_404 actually raises the Http404 exception that the behavior was going to be different than, say, a try block whose exception clause returned HttpResponseNotFound.
>
> 2) Once I had encountered this phenomenon, a quick google search led me to this page from the book:
>
> http://www.djangobook.com/en/beta/chapter16/
>
> ....which seemed, at least for a moment, to verify my previous experience.

Yes - that does seem to suggest 404's don't trigger exception middleware. However, I've checked the code back to the magic-removal merge (in 2005) [1], and I can't see any evidence that 404's have ever been a special case.

[1] https://code.djangoproject.com/browser/django/trunk/django/core/handlers/base.py?rev=2809#L73

The only change to this area that I can see is to make sure that the response raised by the exception middleware is in recent times has been a modification that means that if the exception middleware returns a response, that response goes through the response middleware; back in the days of magic-removal, it would be returned verbatim.

> I think though that I simply hadn't raised Http404 since implementing this middleware. It makes perfect sense that it behaves the way it does.

Yes and no; yes, in that it's an exception; no, in that it's an interesting inconsistency that 404s are (or can be) handled as exceptions, but no other status code is handled as an exception.

Yours,
Russ Magee %-)

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