Bugs item #1162912, was opened at 2005-03-14 06:20 Message generated for change (Comment added) made by rhettinger You can respond by visiting: https://sourceforge.net/tracker/?func=detail&atid=105470&aid=1162912&group_id=5470
Please note that this message will contain a full copy of the comment thread, including the initial issue submission, for this request, not just the latest update. Category: Documentation Group: None Status: Open Resolution: Fixed Priority: 5 Submitted By: Stefan Behnel (scoder) Assigned to: Raymond Hettinger (rhettinger) Summary: typesseq-mutable lacks note on combined key/cmp usage Initial Comment: The documentation about list.sort() and sorted() does not state how the keyword arguments cmp and key interact. Aparently, if key is supplied, cmp works on the result of the key function and no longer on the item itself. This should be documented. ---------------------------------------------------------------------- >Comment By: Raymond Hettinger (rhettinger) Date: 2005-07-04 09:03 Message: Logged In: YES user_id=80475 The docs are not meant to capture all implementation details. Building lookalike objects only need to match the documented, promised behavior -- the rest can be arbitrary. And, yes, it does matter that using the two together is almost always the wrong thing to do. The docs are supposed to point people in the right direction -- it makes Python easier to use. Please revert this patch. ---------------------------------------------------------------------- Comment By: Reinhold Birkenfeld (birkenfeld) Date: 2005-07-04 05:21 Message: Logged In: YES user_id=1188172 But in this case, don't you think that the implementor would in every case look up how it's done in the source code? Raymond, please decide. ---------------------------------------------------------------------- Comment By: Stefan Behnel (scoder) Date: 2005-07-04 04:52 Message: Logged In: YES user_id=313935 ... except, for example, when implementing classes that behave like builtins and stdlib. So, if it's an implementation detail, why not document that and give the hint that the current CPython implementation applies key before cmp? I do not think it matters that using them together is "almost always the wrong thing to do". In that case, it should either become impossible or at least merit an understandable warning in the documentation. ---------------------------------------------------------------------- Comment By: Raymond Hettinger (rhettinger) Date: 2005-07-03 23:13 Message: Logged In: YES user_id=80475 Actually, it should NOT be documented because 1) it is an implementation specific detail and 2) using key and cmp together is almost always the wrong thing to do. ---------------------------------------------------------------------- Comment By: Reinhold Birkenfeld (birkenfeld) Date: 2005-07-03 15:22 Message: Logged In: YES user_id=1188172 Thanks for the report and the patch. Committed as Doc/lib/libstdtypes.tex r1.183, r1.170.2.12. ---------------------------------------------------------------------- Comment By: Peter van Kampen (pterk) Date: 2005-07-03 15:00 Message: Logged In: YES user_id=174455 I have submittted a doc patch (#1231890) that adds a note that reads: If both key and cmp are supplied the key function is applied before the cmp function. (You can check listsort in listobject.c to verify) ---------------------------------------------------------------------- You can respond by visiting: https://sourceforge.net/tracker/?func=detail&atid=105470&aid=1162912&group_id=5470 _______________________________________________ Python-bugs-list mailing list Unsubscribe: http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
