On Tue, Jan 27, 2015 at 4:20 PM, Guido van Rossum <guido@python.org> wrote:
When does a program need *both* absolute and relative tolerance in a single test?
It's reasonably common in numpy, where the equivalent function is vectorized to do multiple checks at once, e.g. here are some tests that mix zeros and non-zeros in a single call: https://github.com/mnick/scikit-tensor/blob/b067ed02ef4b1e3f1cb24004b2f20af5... https://github.com/ricklupton/whales/blob/6bc722c1e2dbadb494fa3d4e83e1cb6415... The equivalent would be writing assert all([math.is_close_to(a, e) for (a, e) in zip(actual, expected)]) where 'expected' has a mix of zeros and non-zeros.
I think that's it for the technical decisions.
I would also appreciate suggestions for paramater names --at least if we go with the asymetric test: "actual" and "expected" is a bit confusing -- I like "expected", but we need something better than "actual" for the don't-know-it's-right one.
I also would really appreciate someone working out the details and contributing text for the inclusion of this in unittest.TestCase -- unittest is really not my thing.
I've pushed some changes to gitHub (sorry, forgot to push yesterday), and once the dust settles I'll incorporate as many of the suggestions in the PEP text as I can.
I still think this is better off as a recipe than as a helper function.
I don't find it super compelling either way -- at the end of the day, if 'math' doesn't provide this then many people will use libraries that will or else write their own. I guess I don't have a good sense of what the audience for 'math' is these days -- I'm sure it has one, but aside from tiny one-off usages I'm not sure what it is. None of the production numerical code I see even bothers importing it. It's possible that it largely serves a kind of pedagogical role? high schoolers learning to program etc.? in which case there might be some more benefit in having a well-documented discussion of the issues here in the stdlib docs. The most compelling argument I see is that if we care about unittest, then it would be good to have a better alternative to assertAlmostEqual. (...I don't know anyone who uses the unittest API directly these days, though!) -n -- Nathaniel J. Smith Postdoctoral researcher - Informatics - University of Edinburgh http://vorpus.org