New submission from Serhiy Storchaka: The int constructor can return an instance of int subclass.
>>> class BadTrunc: ... def __trunc__(self): ... return True ... >>> int(BadTrunc()) True When __int__ returns non-exact int, at least a warning is emitted: >>> class BadInt: ... def __int__(self): ... return True ... >>> int(BadInt()) __main__:1: DeprecationWarning: __int__ returned non-int (type bool). The ability to return an instance of a strict subclass of int is deprecated, and may be removed in a future version of Python. True The constructor of int subclass always return an instance of correct type: >>> class IntSubclass(int): ... pass ... >>> type(IntSubclass(BadTrunc())) <class '__main__.IntSubclass'> >>> type(IntSubclass(BadInt())) __main__:1: DeprecationWarning: __int__ returned non-int (type bool). The ability to return an instance of a strict subclass of int is deprecated, and may be removed in a future version of Python. <class '__main__.IntSubclass'> I don't know if it is worth to deprecate __trunc__ returning non-exact int, since this special method is used in math.trunc(). But I think that the int constructor should convert its result to exact int. If some preparatory period is needed, it can first start to emit FutureWarning. ---------- components: Interpreter Core messages: 265196 nosy: mark.dickinson, serhiy.storchaka priority: normal severity: normal status: open title: int() can return not exact int instance type: behavior versions: Python 3.6 _______________________________________ Python tracker <rep...@bugs.python.org> <http://bugs.python.org/issue26984> _______________________________________ _______________________________________________ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
