Raymond Hettinger <rhettin...@users.sourceforge.net> added the comment:
The basic problem here is that the "one obvious way" to some people (including me and Martin v. Löwis) is to use a dictionary. Further, there is the problem of conflating types in a user's mind -- right now, dictionaries are all about looking up and returning values, while sets are not. The current notion of sets corresponds neatly with what folks learn in their basic math classes. In contrast, the notion of "canonical representatives of an equivalence class" is a more advanced mathematical concept, one that many people are never taught. This is even more problematic in Python because the operation of finding canonical values is hidden behind well designed __hash__ and __eq__ functions (for example, it is not at all obvious how Decimal(3.0), float(3.0), and int(3.0) all have the same hash value). An additional problem is the modification of set.add() so that it violates Python's norm of having mutating methods return None. We should keep the language consistent in this regard. Also, I should comment on the "appreciable memory savings". This saves only a single pointer (4 bytes on a 32-bit build) out of three per string. But the string object itself takes up memory, so the percent savings per string is smaller than you would might expect (typically less than 15%). Finally, the spirit of the language moratorium is to make it so that other Python implementations don't have to change for a few years. FWIW, I am already going to expand the set/frozenset documention to show some techniques for accessing and using sets. I can add a link to a get_equivalent() recipe that makes it possible to retrieve canonical values from any container including sets. That recipe uses all the containers as-is, no patching or API changes needed. ---------- _______________________________________ Python tracker <rep...@bugs.python.org> <http://bugs.python.org/issue7224> _______________________________________ _______________________________________________ Python-bugs-list mailing list Unsubscribe: http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
