Multi version support for Python doctests

Question

I am writing my doctests like this:

>>> some_function(a=1, b=2)
{u'id': u'123', u'name': u'abc'}

This works fine for Python version 2.5, 2.6 & 2.7 but fails for Python 3 with following error:

Expected:
    {u'id': u'123', u'name': u'abc'}
Got:
    {'id': '123', 'name': 'abc'}

Problem is that if I write my doctests like this:

>>> some_function(a=1, b=2)
{'id': '123', 'name': 'abc'}

They will work only for Python3 and fail on Python2 version. My question is how do I make it cross version compatible?

You'll have to use the same techniques as you'd use for making your code work in both Python 2.x and 3.x. That can get ugly, fast. Personally, I'd stick with unittests instead of doctests and use Sphinx for API documentation. — Martijn Pieters♦
I do use unittest for testing, this is just to validate the examples. — Irfan
Have you tried with Python 3.3? 3.3 reintroduces the u"" syntax (docs.python.org/3/whatsnew/3.3.html). Don't know if the change will affect doctests, but it is worth a try. — codeape
@codeape: You can use u'' to specify a literal, but repr(somestring) will not use them, so the tests still will fail. Compare that to using r'' raw python literals; the r will be dropped from the representation as well. — Martijn Pieters♦
OK, I see. I guess the only way to do this with doctests would be to rewrite the tests, then. For instance >>> result = some_function(a=1, b=2) >>> print(result["id"]) etc. — codeape

Thomas K Thomas K · Accepted Answer · 2012-11-20T13:21:28

I ran into the same problem with doctests in IPython. There's no neat solution, but I wrapped all of the u' prefixes in {}, i.e. {u}', and made a little function that would include or exclude them as appropriate.

You can see the u_format() function and a doctest using it.

But that's rather messy, so I've moved many tests away from doctests.

Alternatively, you can test it like this:

>>> some_function(a=1, b=2) == {'id': '123', 'name': 'abc'}
True

If you need some unicode strings in the keys, you can use u'abþ', and use distribute to run 2to3 on the doctests. But that only works on input code, not output reprs.

Multi version support for Python doctests

3 Answers