Mark Dickinson added the comment: See the related python-dev discussion started by Mark Shannon here:
http://mail.python.org/pipermail/python-dev/2013-March/125022.html and continuing well into April here: http://mail.python.org/pipermail/python-dev/2013-April/125042.html The consensus that emerged from that thread seems to be that calls to operator.index and to int() should always return something of exact type int. The attached patch: - Raises TypeError for implicit calls to nb_int that fail to return something of exact type int. (Results of direct calls to __int__ are not checked.) - Ensures that *all* conversions from a non-int to an int via nb_int make use of the nb_int slot, even for int subclasses. Prior to this patch, some of the PyLong_As... functions would bypass __int__ for int subclasses. - Adds a new private _PyLong_FromNbInt function to Objects/longobject.c, so that we have a single place for performing these conversions and making type checks, and refactors existing uses of the nb_int slot to go via this function. - Makes corresponding changes for nb_index, which should address the original bug report. I guess this may be too dangerous a change for Python 3.4. In that case, I propose raising warnings instead of TypeErrors for Python 3.4 and turning those into TypeErrors in Python 3.5. One other question: should direct calls to __int__ and __index__ also have their return values type-checked? That doesn't seem to happen at the moment for other magic methods (see below), so it would seem consistent to only do the type checking for interpreter-generated implicit calls to __int__ and __index__. Nick: any opinion? >>> class A: ... def __len__(self): return "a string" ... def __bool__(self): return "another string" ... >>> a = A() >>> a.__len__() 'a string' >>> a.__bool__() 'another string' >>> len(a) Traceback (most recent call last): File "<stdin>", line 1, in <module> TypeError: 'str' object cannot be interpreted as an integer >>> bool(a) Traceback (most recent call last): File "<stdin>", line 1, in <module> TypeError: __bool__ should return bool, returned str ---------- assignee: docs@python -> mark.dickinson components: +Interpreter Core -Documentation keywords: +patch nosy: +ncoghlan Added file: http://bugs.python.org/file31147/issue17576.patch _______________________________________ Python tracker <rep...@bugs.python.org> <http://bugs.python.org/issue17576> _______________________________________ _______________________________________________ Python-bugs-list mailing list Unsubscribe: http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
