[Python-bugs-list] [ python-Bugs-475877 ] Mutable subtype instances are hashable (original) (raw)

noreply@sourceforge.net noreply@sourceforge.net
Sun, 28 Oct 2001 19:24:03 -0800

Bugs item #475877, was opened at 2001-10-28 19:24 You can respond by visiting: http://sourceforge.net/tracker/?func=detail&atid=105470&aid=475877&group_id=5470

Category: Type/class unification Group: Python 2.2 Status: Open Resolution: None Priority: 7 Submitted By: Tim Peters (tim_one) Assigned to: Guido van Rossum (gvanrossum) Summary: Mutable subtype instances are hashable

Initial Comment:

class D(dictionary): pass ... d = D() hash(d) 7920544 id(d) 7920544

Ditto for instances of list subclasses:

class L(list): pass ... x = L(range(100)) hash(x) 7928992 id(x) 7928992

Among other nasties, this lets them get used as mutable dict keys.

Reported by Mark J on c.l.py:

""" From: Mark J <maj64@hotmail.com> Sent: Sunday, October 28, 2001 10:03 PM To: python-list@python.org Subject: Python 2.2b1 hashable dictionary bug?

Since I haven't had a good hit rate at detecting bugs vs. features, I thought I'd post here before filing a bug report at SourceForge.

Python 2.2b1 (#1, Oct 19 2001, 23:11:09) [GCC 2.96 20000731 (Red Hat Linux 7.1 2.96-81)] on linux2 Type "help", "copyright", "credits" or "license" for more information.

class D(dictionary): pass ... d = {} d2 = D() d[d2] = "dictionary used as key" d {{}: 'dictionary used as key'} d[D()]="now have two keys that look the same" d {{}: 'now have two keys that look the same', {}: 'dictionary used as key'} d2["key"] = "mutable key in d" d {{}: 'now have two keys that look the same', {'key': 'mutable key in d'}: 'dictionary used as key'} d[d] = "plain dictionary not allowed as key" Traceback (most recent call last): File "", line 1, in ? TypeError: unhashable type d2[d2] = "subclassed dictionary allowed though" d2 {{...}: 'subclassed dictionary allowed though', 'key': 'mutable keys'} #whoa: what just happened: {...} ??

Interesting.... So is this a feature or a bug? """

You can respond by visiting: http://sourceforge.net/tracker/?func=detail&atid=105470&aid=475877&group_id=5470