Hi all, Over on the Python-ideas list, there's a thread about the new statistics module, and as the author of that module, I'm looking for a bit of guidance regarding backwards compatibility. Specifically two issues:
(1) With numeric code, what happens if the module become more[1] accurate in the future? Does that count as breaking backwards compatibility? E.g. Currently I use a particular algorithm for calculating variance. Suppose that for a particular data set, this algorithm is accurate to (say) seven decimal places: # Python 3.4 variance(some_data) == 1.23456700001 Later, I find a better algorithm, which improves the accuracy of the result: # Python 3.5 or 3.6 variance(some_data) == 1.23456789001 Would this count as breaking backwards compatibility? If so, how should I handle this? I don't claim that the current implementation of the statistics module is optimal, as far as precision and accuracy is concerned. It may improve in the future. Or would that count as a bug-fix? "Variance function was inaccurate, now less wrong", perhaps. I suppose the math module has the same issue, except that it just wraps the C libraries, which are mature and stable and unlikely to change. The random module has a similar issue: http://docs.python.org/3/library/random.html#notes-on-reproducibility (2) Mappings[2] are iterable. That means that functions which expect sequences or iterators may also operate on mappings by accident. For example, sum({1: 100, 2: 200}) returns 3. If one wanted to reserve the opportunity to handle mappings specifically in the future, without being locked in by backwards-compatibility, how should one handle it? a) document that behaviour with mappings is unsupported and may change in the future; b) raise a warning when passed a mapping, but still iterate over it; c) raise an exception and refuse to iterate over the mapping; d) something else? Question (2) is of course a specific example of a more general question, to what degree is the library author responsible for keeping backwards compatibility under circumstances which are not part of the intended API, but just work by accident? [1] Or, for the sake of the argument, less accurate. [2] And sets. -- Steven _______________________________________________ Python-Dev mailing list Python-Dev@python.org https://mail.python.org/mailman/listinfo/python-dev Unsubscribe: https://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com
