[Python-Dev] [Python-checkins] r45321 - in python/trunk: Lib/test/test_traceback.py Lib/traceback.py Misc/NEWS (original) (raw)

Tim Peters tim.peters at gmail.com
Thu Apr 13 04:02:10 CEST 2006

[Tim]

... Fine by me if we change the failing tests on the trunk to pass (noting that should have been done before checking in).

[Phillip]

It's not fine by me if the reason for the failure is that doctests trapping specific exceptions no longer work with the patch.> If that's the case, the patch should be reverted entirely, absent any compelling reasoning for breaking everyone else's doctests in 2.5.

I agree with the patch author's position that "it's a bug" that the traceback module's functions' output doesn't match the interpreter's traceback output. That certainly wasn't intended; it's most likely left over from the days when only strings could be exceptions, and nobody noticed that the old traceback-module code "didn't work exactly right" anymore when the notion of exceptions was generalized.

WRT doctests, it's a mixed bag. Yes, some tests will fail. doctests are always vulnerable to changes "like this". OTOH, the change also simplifies writing new doctests. I remember being baffled at doing things like:

import decimal 1 / decimal.Decimal(0) Traceback (most recent call last): File "", line 1, in ? File "C:\Python24\lib\decimal.py", line 1314, in rdiv return other.div(self, context=context) File "C:\Python24\lib\decimal.py", line 1140, in div return self._divide(other, context=context) File "C:\Python24\lib\decimal.py", line 1222, in _divide return context._raise_error(DivisionByZero, 'x / 0', sign) File "C:\Python24\lib\decimal.py", line 2267, in _raise_error raise error, explanation decimal.DivisionByZero: x / 0

in an interactive shell, pasting it into a doctest, and then seeing the doctest fail because the exception name "somehow" magically changed to just "DivisionByZero". I got used to that before I found time to understand it, though. Future generations wouldn't suffer this cognitive dissonance.

A less-desirable (IMO) alternative is to change the Python core to display bare (non-dotted) exception names when it produces a traceback. The fundamental bug here is that the core and the traceback module produce different tracebacks given the same exception info, and changing either could repair that.

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