[TIP] Using coverage.py with code that uses sys.settrace()

[Ned Batchelder]

Yeah, sys.settrace() could be more sophisticated.  However you are 
setting the trace function, I would think you could manage to set it 
back somehow.  But even if you could, you wouldn't be getting coverage 
measurement for the time your trace function was in effect, unless you 
also call my trace function from yours.  A mess all around.

--Ned.

On 12/29/2011 4:22 AM, Leahy, Oliver wrote:
>
> Thanks for the suggestions, I've tried the --timid flag, hasn't 
> helped. And unfortunately
>
> (for me) it looks like I can't successfully reset the trace function 
> with settrace() because of
>
> the way my trace functions work; I raise exceptions when I reached 
> specified points in the
>
> code, so once the exception is raised I don't get an opportunity to 
> call sys.settrace().
>
> So I'm going to have to use mocks, as you suggest. What I really want 
> is for sys.settrace() to
>
> be able to manage a stack of functions that would be called in sequence J
>
> Thanks again,
>
> Ollie
>
> *From:*Ned Batchelder [mailto:ned at nedbatchelder.com]
> *Sent:* 28 December 2011 21:44
> *To:* Leahy, Oliver
> *Cc:* testing-in-python at lists.idyll.org
> *Subject:* Re: [TIP] Using coverage.py with code that uses sys.settrace()
>
> On 12/28/2011 10:58 AM, Leahy, Oliver wrote:
>
> What's the recommended way to use coverage.py with code that uses 
> sys.settrace()
>
> I'm using settrace() to simulate error conditions at certain lines 
> during testing, but
>
> this interferes with the use coverage.py makes of settrace() and I'm 
> getting incorrect
>
> coverage metrics.
>
> I'm hacking at my code to try to store an existing value for 
> sys.gettrace() whenever
>
> I call settrace(),  and then restoring the pre-existing trace function 
> whenever I stop
>
> tracing using my function, but it's not working for me at the moment.
>
> Is this a sensible approach to this problem?  Would anyone have any 
> other suggestions?
>
> I don't know if anyone has tried measuring code that uses settrace.  
> You should be able to use gettrace and settrace to save and restore 
> the coverage trace function, but I won't be that surprised if it isn't 
> working.  You should try using the --timid flag on "coverage run" to 
> see if it helps.  It's specifically for environments that do unusual 
> things with settrace().  Are you sure settrace() is the best way to 
> accomplish your goals? Mocking can also inject errors into running 
> code, and may be easier to work with in the long run.
>
> In any case, if you need more help, post more details.
>
> --Ned.
>
> Thanks,
>
> Ollie
>
>
>
>
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