On 4/4/06, Guido van Rossum <[EMAIL PROTECTED]> wrote: > On 4/4/06, Crutcher Dunnavant <[EMAIL PROTECTED]> wrote: > > On 4/4/06, Greg Ewing <[EMAIL PROTECTED]> wrote: > > > Crutcher Dunnavant wrote: > > > > > > > A) issubclass() throws a TypeError if the object being checked is not > > > > a class, which seems very strange. > > > > > > If I ever pass a non-class to issubclass() it's almost > > > certainly a bug in my code, and I'd want to know about > > > it. > > > > Perhaps, but is it worth distorting a predicate? > > Certainly. In other languages this would be a compile-time error.
In other, statically typed languges. Someone hands me X, I want to know if X is a subclass of Y. Yes or No. If X is not a class, then it is not a subclass of Y, hence issubclass(X, Y) should return False. > There's no rule that predicate cannot raise an exception. No, but it makes many applications (such as using it as a test in list comprehensions) difficult enough to not be worth it. > If you're not sure whether something is a class or not, you should > first sniff it out for its class-ness before checking whether it's a > subclass of something. I recommend hasattr(x, "__bases__") which is > more likely to recognize classes than isinstance(x, type) -- the > latter only works for standard new-style classes. > > > > On the rare occasions when I don't want this, I'm > > > happy to write > > > > > > isinstance(c, type) and issubclass(c, d) > > > > This doesn't work, did you mean? > > isinstance(c, types.ClassType) and issubclass(c, d) > > > > > > > > B) issubclass() won't work on a list of classs, > > > > the way isinstance() does. > > > > > > That sounds more reasonable. I can't think of any > > > reason why it shouldn't work. > > Agreed. > > -- > --Guido van Rossum (home page: http://www.python.org/~guido/) > -- Crutcher Dunnavant <[EMAIL PROTECTED]> littlelanguages.com monket.samedi-studios.com _______________________________________________ Python-Dev mailing list Python-Dev@python.org http://mail.python.org/mailman/listinfo/python-dev Unsubscribe: http://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com
