Bugs item #1368768, was opened at 2005-11-28 20:40 Message generated for change (Comment added) made by collinwinter You can respond by visiting: https://sourceforge.net/tracker/?func=detail&atid=105470&aid=1368768&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: Feature Request Status: Open Resolution: None Priority: 5 Submitted By: Mike Meyer (mwm) Assigned to: Nobody/Anonymous (nobody) Summary: clearing up dictionary keys/set member docs Initial Comment: The documentation for dictionaries says "A dictionary's keys are almost arbitrary values. Only values containing lists, dictionaries or other mutable types (that are compared by value rather than by object identity) may not be used as keys." This is wrong. tuples are an immutable type, but not all tuples can be used as keys. The set documentation says "A set object is an unordered collection of immutable values.". This is also wrong - at least for common definitions of immutable. Immutability is a convenient way of dealing with builtin types, but is a red herring. It's whether or not the object has a hash value that matters, and it's the behavior of that hash value (coupled with comparison) that determine whether or not things behave as expected. The __hash__ documentation deals with these issues. I suggest replacing the current descriptions with one that references hashing, and a footnote pointing to the __hash__ docs for details: Any hashable object(1) can be used as a dictionary key/set element. Lists, sets and dicts are not hashable, and can not be used. Tuples can be used if all the things they contain are hashable. Instances of all other built-in types and most user-defined classes are hashable. (1) Objects for which the hash() function returns an appropriate value. See the __hash__ documentation for details. ---------------------------------------------------------------------- Comment By: Collin Winter (collinwinter) Date: 2006-01-05 07:28 Message: Logged In: YES user_id=1344176 I have submitted patch #1397711 which resolves this issue. ---------------------------------------------------------------------- You can respond by visiting: https://sourceforge.net/tracker/?func=detail&atid=105470&aid=1368768&group_id=5470 _______________________________________________ Python-bugs-list mailing list Unsubscribe: http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
