On Sep 16, 3:23 am, Casey <casey.mcgi...@gmail.com> wrote: > I noticed that the many (if not all) classes in threading.py[1] all > inherit from object, yet non of the init methods call super(). I am > curious as to why this is the chosen implementation? If the benefit of > new-style classes is to support multiple inheritance, then isn't this > "broken" if the class __init__ method does not make a call to super?
The Python language supports multiple inheritance but it doesn't mean all classes are required to support it. Anyway, I wouldn't recommend using MI on classes you (or your company) don't control yourself, unless the class is explicitly documented as supporting MI. (For that matter, I wouldn't recommend single inheritance in that situation.) This is not just because of issues with super. Inheritance is trickier than most people expect; you can't reliably inherit without knowing and depending on some implementation details of the base class (**). This is true even without super's defects. If the base class is under your control, no problem, multiply inherit at will. If the base class is documented as supporting multiple inheritance, then you are fairly safe because the class is unlikely to change in such a way as to break any derived classes. So go ahead. If neither applies, well you're on your own. Carl Banks (**) For instance, some container class might define a __setitem__ method, and also some higher level methods like add. If you want to subclass it, can you just override __setitem__, or do you have to override higher-level methods like add also? You don't know unless you know how add is implemented. A lot of people seem to think that all you need to know about the base class to inherit from it is the interface, or rather, it would be all you'd need to know if not for the super issue. Then they turn around and complain that super is broken because it is the only thing preventing us from reaching this panacean realm where one can inherit from any base class at all without care. Alas it was never so. Care has always been required when inheriting. -- http://mail.python.org/mailman/listinfo/python-list
