[Python-Dev] doctest, unicode repr, and 2to3 (original) (raw)

Barry Warsaw barry at python.org
Fri Mar 5 05:30:12 CET 2010


On Mar 05, 2010, at 05:11 AM, Martin v. Löwis wrote:

Johan Harjano ran into an interesting problem when trying to run the Django test suite under Python 3.1.

Django has doctests of the form

a6.headline u'Default headline' Even when converting the doctest with 2to3, the expected output is unmodified. However, in 3.x, the expected output will change (i.e. not produce an u"" prefix anymore).

For this reason, I always recommend using print, even though...

Now, it might be possible to reformulate the test case (e.g. use print() instead of relying on repr), however, this is undesirable as a) the test should continue to test in 2.x that the result object is a unicode string, and b) it makes the test less readable.

If you really want to test that it's a unicode, shouldn't you actually test its type? (I'm not sure what would happen with that under 2to3.) Besides, the type of the string is very rarely important, so I think the u-prefix and quotes is mostly just noise.

I would like to find a solution where this gets automatically corrected, e.g. through 2to3, or through changes to doctest, or through changes of str.repr.

I think Michael was also talking about changes to doctest that would automatically sort dictionaries and sets. Again, it's not hard to write doctests correctly, but it's surprisingly common to implicitly rely on sort order.

I think the right place to change these is in doctest.

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