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Re: Missing something on exception handling in Python 3

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  Re: Missing something on exception handling in Python 3 Skip Montanaro <skip@pobox.com> - 2013-08-27 00:00 -0500
    Re: Missing something on exception handling in Python 3 Steven D'Aprano <steve@pearwood.info> - 2013-08-27 09:22 +0000

#53030 — Re: Missing something on exception handling in Python 3

I found this question/answer on Stack Overflow:

http://stackoverflow.com/questions/15123137

but after fiddling around with it, I can't find a solution that works
for Python 3.2 and 3.3, let alone 2.x.  In 3.2, exceptions have both
__cause__ and __context__ attributes.  I tried setting both to None
(in 3.2), but I still get the full double traceback:

>>> try: 1/0
... except ZeroDivisionError:
...    exc = TypeError()
...    exc.__context__ = None
...    exc.__cause__ = None
...    raise exc
...
Error in sys.excepthook:
IndexError: tuple index out of range

Original exception was:
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ZeroDivisionError: division by zero

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "<stdin>", line 6, in <module>
TypeError

The sys.excepthook error is because I have a custom interactive
sys.excepthook, which is itself apparently broken in Python 3.2.

I've looked at PEP 409 and 415, but just get more confused.

*sigh*

Maybe I'll try again tomorrow when I've had a bit of sleep... and take
a closer look at Ethan's suggestion.

Skip

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#53042

On Tue, 27 Aug 2013 00:00:36 -0500, Skip Montanaro wrote:

> I found this question/answer on Stack Overflow:
> 
> http://stackoverflow.com/questions/15123137
> 
> but after fiddling around with it, I can't find a solution that works
> for Python 3.2 and 3.3, let alone 2.x.  In 3.2, exceptions have both
> __cause__ and __context__ attributes.  I tried setting both to None (in
> 3.2), but I still get the full double traceback:


Yes, "raise from None" only works in Python 3.3.

My way of dealing with this is to use "raise from None" and just accept 
that 3.1 and 3.2 users will see double tracebacks :-(

All the more reason to encourage people to go straight to 3.3 or better 
and skip 3.1 and 3.2 :-)



-- 
Steven

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