[Twisted-Python] how to write a safe catch-all

Chris Withers chris at simplistix.co.uk
Thu Sep 30 10:13:50 EDT 2010

On 30/09/2010 14:39, Jonathan Lange wrote:
> On Thu, Sep 30, 2010 at 2:36 PM, Chris Withers<chris at simplistix.co.uk>  wrote:
> ...
>> Is there any way I can get both errbacks *and* exceptions handled nicely in
>> my `loop` call?
> You know about defer.maybeDeferred, right?

Yep, the problem is with `loop` implemented like so:

def loop():
     d = maybeDeferred(doStuff)
     d.addErrback(partial(log.err,_why='Unhandled scheduled exception'))

...the logging is odd:

2010-09-30 15:07:03,161 ERROR   : log         (22194|7f41910b26e0): 
Unhandled Error
Traceback (most recent call last):
   File "test_looping.py", line 47, in <module>
   File "/twisted/internet/base.py", line 1166, in run
   File "/twisted/internet/base.py", line 1175, in mainLoop
--- <exception caught here> ---
   File "/twisted/internet/base.py", line 779, in runUntilCurrent
     call.func(*call.args, **call.kw)
   File "test_looping.py", line 30, in __call__
     del self.connector
exceptions.AttributeError: Break instance has no attribute 'connector'

called  4
called  5
/twisted/internet/defer.py:262: DeprecationWarning: Don't pass strings 
(like 'Break!') to failure.Failure (replacing with a DefaultException).
   fail = failure.Failure(fail)
2010-09-30 15:07:05,167 ERROR   : log         (22194|7f41910b26e0): 
Unhandled scheduled exception
Traceback (most recent call last):
Failure: twisted.python.failure.DefaultException: Break!

So, how come my log.err doesn't get used for the AttributeError on 



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