[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
Sat Apr 15 06:42:28 CEST 2006

[John J Lee]

Assuming this is fixed in 2.5 final, is there some way to write doctests that work on both 2.4 and 2.5? If not, should something like doctest.IGNOREEXCEPTIONDETAIL be added -- say IGNOREEXCEPTIONMODULE?

[also John]

Sorry, please ignore the post of mine I'm replying to here.

I missed part of the thread, and Tim has already answered my question...

That's news to Tim ;-) It's not possible to add a new doctest option in 2.5 that would allow a doctest to work under both 2.4 and 2.5: the test would blow up under 2.4, because 2.4's doctest wouldn't recognize the (new in 2.5) option, and would raise a ValueError of its own griping about the unknown option name.

It would be possible to add a new doctest option in 2.5 that would (just) allow a doctest running under 2.5 to accept a bare "name" in an exception despite that the traceback module changed in 2.5 to produce "some.dotted.name" instead. That doesn't seem very useful, though (as above, it would force the test to fail when run under 2.4).

Of course a doctest can contain any Python code, so there are many ways to write a doctest that passes under all versions of Python, without active help from doctest. For example, using the running example in this thread, this way works under all versions of Python with a decimal module:

"""

import decimal try: 1 / decimal.Decimal(0) except decimal.DivisionByZero: print "good" good """

Oddly enough, ELLIPSIS doesn't actually work for this purpose:

"""

import decimal 1 / decimal.Decimal(0) #doctest: +ELLIPSIS Traceback (most recent call last): [etc] ...DivisionByZero: x / 0 """

That test fails under 2.4, and would also fail under the presumably changed 2.5. The problem is that, as the docs say, when trying to guess where an exception message starts, doctest skips down to the first line after the "Traceback" line indented the same as the "Traceback" line and starting with an alphanumeric character. There is no such line in this example (the exception line starts with a period), so doctest believes the example is showing expected stdout, not that it's showing an exception. The delightfully baffling result is that doctest complains that the example raises an exception when an exception wasn't expected. Stinking magic ;-)

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