Bugs item #1328278, was opened at 2005-10-16 18:22 Message generated for change (Comment added) made by stupidgeekman You can respond by visiting: https://sourceforge.net/tracker/?func=detail&atid=105470&aid=1328278&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: Python Interpreter Core Group: Python 2.4 Status: Closed Resolution: Wont Fix Priority: 5 Private: No Submitted By: Josh Marshall (jpmarshall) Assigned to: Nobody/Anonymous (nobody) Summary: __getslice__ taking priority over __getitem__ Initial Comment: When creating a class that uses __getitem__ to implement slicing, if __getattr__ is also implemented, slicing will fail. This is due to the (deprecated) __getslice__ method being called before __getitem__. The attached file demonstrates this. If __getitem__ is implemented on its own, all is rosy. When we add __getattr__ and do not raise an AttributeError when __getslice__ is searched for, the slicing fails. If we raise this AttributeError, __getitem__ is called next. The only other reference I could find to this bug is on the jython mailing list, from 2003: http://sourceforge.net/mailarchive/forum.php? thread_id=2350972&forum_id=5586 My question is; why is __getslice__ called before __getitem__? I assumed that because it is deprecated, it would be the last resort for a slicing. Is this planned to be fixed, or is there existing behaviour that is reliant on it? ---------------------------------------------------------------------- Comment By: Tim (stupidgeekman) Date: 2007-03-14 19:33 Message: Logged In: YES user_id=1743956 Originator: NO I would suggest that the list class should use the same form suggested on the documentation site, namely: if sys.version_info < (2, 0): # They won't be defined if version is at least 2.0 final def __getslice__(self, i, j): return self[max(0, i):max(0, j):] def __setslice__(self, i, j, seq): self[max(0, i):max(0, j):] = seq def __delslice__(self, i, j): del self[max(0, i):max(0, j):] ... in order to assure that the *slice methods are not defined unless needed for backward compatability in an older interpreter; then classes developed with the above suggested structure should work properly. ---------------------------------------------------------------------- Comment By: Georg Brandl (birkenfeld) Date: 2005-11-11 11:50 Message: Logged In: YES user_id=1188172 You're correct. __getslice__ is supported for backwards compatibility, and its semantics cannot change (before 3.0, that is). ---------------------------------------------------------------------- Comment By: Thomas Lee (krumms) Date: 2005-11-10 06:48 Message: Logged In: YES user_id=315535 This seems to be the documented, expected behavior: http://www.python.org/doc/2.4.2/ref/sequence-methods.html As to _why_ __getslice__ is called before __getitem__, I'm not sure - but it's right there in the docs. ---------------------------------------------------------------------- You can respond by visiting: https://sourceforge.net/tracker/?func=detail&atid=105470&aid=1328278&group_id=5470 _______________________________________________ Python-bugs-list mailing list Unsubscribe: http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
