On Tuesday 17 January 2017 20:37, Antoon Pardon wrote: > Op 17-01-17 om 08:05 schreef Steven D'Aprano: >> I wish to emulate a "final" class using Python, similar to bool: >> >> py> class MyBool(bool): >> ... pass >> ... >> Traceback (most recent call last): >> File "<stdin>", line 1, in <module> >> TypeError: type 'bool' is not an acceptable base type [...] > I find those kind of classes annoying as hell and nobody has ever given me a > good reason for them. What good was it to change Lock from a factory function > to a class if you can't subclass the result anyway.
I'm not sure which Lock class you're referring to. > The result will probably be that users that would prefer to subclass your > class will monkey-patch it. Something like: > > class MyLock: > def __init__(self): > self.lock = Lock() > > def __getattr__(self, attr): > return getattr(self.lock, attr) That technique is called "delegation", or sometimes "composition". > So I wonder what reasons do you have prefering that your users monkey-patch > your class instead of subclassing it? Since my class provides no useful behaviour, I don't think anyone will seriously have any reason to subclass it. Python has at least three singleton instances which are used purely as abstract symbols: they have no state, and very little behaviour besides a nice repr. They are None, NotImplemented and Ellipsis. I'm effectively trying to make my own abstract symbol. But it's mostly a learning exercise. -- Steven "Ever since I learned about confirmation bias, I've been seeing it everywhere." - Jon Ronson -- https://mail.python.org/mailman/listinfo/python-list
