[Twisted-Python] How to find out if exceptions are being raised in your errBack?

Steve Steiner (listsin) listsin at integrateddevcorp.com
Wed Oct 14 07:31:02 EDT 2009

On Oct 14, 2009, at 3:22 AM, Andrew Bennetts wrote:

> Glyph Lefkowitz wrote:
> [...]
>>   I'm answering a question you didn't ask, about logged errors,  
>> because I
>>   think it's the one you meant to ask.  The answer to the question  
>> you are
>>   actually asking here, i.e. "how do I handle errors in an  
>> errback", is
>>   quite simple: add another errback.  This is sort of like asking  
>> how to
>>   handle exceptions in an 'except:' block in Python.  For example,  
>> if you
> [...]
> To think about it another way, what happens when an unhandled  
> exception occurs
> in a thread?  The thread dies, and Python simply throws the  
> traceback at stderr.
> There's not much else it can reasonably do.  If you want to catch  
> (or suppress)
> that error, you add (another) try/except at the outermost layer of  
> the call
> stack.

Yah, I started thinking about how far out I'd have to start the try/ 
except and started to get a headache when I thought about how much  
code it would have to encompass or, with an alternate approach, how  
many zillions of little extra blocks I'd have to insert everywhere.

> Possibly Twisted could provide some sort of last-ditch error  
> reporting hook,
> like sys.excepthook in core Python, but I'm not sure it would offer  
> much
> advantage over writing a log observer that looks for events where  
> isError is
> set.

I'm going to use the log observer option with tail -f in a separate  
console window on a linux console that's just sitting there doing  
nothing anyway.  That way, if it shows up on that terminal, something  
bad is happening.



More information about the Twisted-Python mailing list