[Web-SIG] some questions about start_response implementation

Phillip J. Eby pje at telecommunity.com
Mon Oct 15 18:11:39 CEST 2007

At 05:52 PM 10/15/2007 +0200, Manlio Perillo wrote:
>I'm implementing the start_response callable for Nginx mod_wsgi and I
>have a few questions.
>1) From the WSGI PEP it seems that an implementation is allowed to
>     *always* raise an exception when start_response is called with a not
>     null exc_info.
>     Is this true?

Yes - as long as it's the exc_info passed in, i.e.:

         raise exc_info[0], exc_info[1], exc_info[2]
         del exc_info

(this pattern of raising prevents the possibility of a reference 
cycle passing through the current stack location, keeping lots of 
objects around longer than necessary)

>2) What happens if an application call start_response with an incorrect
>     status line or headers?
>     Should an implementation consider the function "called", so that an
>     application can call it a second time, *without* the exc_info
>     parameter?

Interesting point.  I think it would be compliant either way, though.

(I'm skipping your third question because it doesn't matter how many 
frameworks use exc_info; if you're implementing WSGI 1.0 you have to 
support it.)

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