On Wed, 29 Sep 2010 02:20:55 +0100, MRAB wrote: > On 29/09/2010 01:19, Terry Reedy wrote:
>> A person using instances of a class should seldom use special names >> directly. They are, in a sense, implementation details, even if >> documented. The idiom "if __name__ == '__main__':" is an exception. >> > __file__ is another exception. As are __iter__, __next__, __add__, __dict__, and, yes, __class__, to say nothing of all the other special methods. I'm afraid that I have to disagree with Terry here. Double-underscore special variables don't start with double underscores because they're implementation details, or to indicate that they're private. They are reserved names for attributes or methods that have special meaning to Python. An implementation that didn't use __dict__ for the namespace of an ordinary class, or didn't call __add__ for the + operator, would be considered to be buggy. Naturally one has to be careful about the assumptions you make with such special methods. You shouldn't assume, for example, that all classes will have a __dict__ attribute. If the class has __slots__ defined, it may not. But I think that it is safe to assume any object will have a __class__ attribute. At least, I'd report it as a bug if I found one that didn't. (This may change in the future. Given type(), and isinstance(), I'm not sure what value __class__ adds.) -- Steven -- http://mail.python.org/mailman/listinfo/python-list
