[Twisted-Python] lost tracebacks?

[glyph at divmod.com]

On 12:41 am, alecf at metaweb.com wrote:
>I traced this down to the code in Deferred._runCallbacks() which does 
>a try: / except: with::
>
>     self.result = failure.Failure()
>
>Seems like this code should say::
>
>     exc_type, exc_value, exc_traceback = sys.exc_info()
>     self.result = failure.Failure(exc_value, exc_type, exc_traceback)

Those are basically equivalent.  Observe:
>>>from twisted.python.failure import Failure
>>>try:
...  1/0
... except:
...  f = Failure()
...
>>>f.printTraceback()
Traceback (most recent call last):
--- <exception caught here> ---
  File "<stdin>", line 2, in <module>

exceptions.ZeroDivisionError: integer division or modulo by zero

Note how it remembers the line number in the traceback.  Your traceback 
must be getting lost for some other reason.