[Twisted-Python] Tracebacks being dropped from exceptions when using inlineCallbacks

Phil Christensen phil at bubblehouse.org
Mon Jan 12 21:58:44 EST 2009

On Jan 12, 2009, at 8:36 PM, Terry Jones wrote:
> I think I've finally gotten to the bottom of why exceptions  
> sometimes lose
> their tracebacks when using inlineCallbacks.
[snip snip]
> I'll stop for now. I have some suggestions for fixes, but I'm  
> already in
> over my head.
> BTW, I get the impression that the Twisted core developers don't  
> really use
> inlineCallbacks. Is that correct?

I don't have a whole lot to contribute here, except to encourage  
discussion of this issue. I *love* inlineCallbacks, and have found the  
availability of the technique has made me far more inclined to chose  
Twisted as the basis for applications that will require a great deal  
of serial-but-asynchronous operations.

I don't know if I've run into this particular issue, but I know that I  
have run into some error-handling issues when using inlineCallbacks  
that I wasn't able to debug in the usual ways, but I think I ended up  
just fixing the bug that I was trying to catch at the time.

My impression is that there's a reluctance to advertise  
inlineCallbacks too loudly, since using it still requires a thorough  
understanding of Deferreds and asynchronous development to be used  
effectively. New users really need to be starting with the 'old- 
fashioned-way', and even experienced users must be careful that their  
'mental model' of what the code is doing actually reflects reality...


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