> On 14 Oct 2017, at 16:37, Martin Teichmann <lkb.teichm...@gmail.com> wrote: > >> Things that will not work if Enum does not have a metaclass: >> >> list(EnumClass) -> list of enum members >> dir(EnumClass) -> custom list of "interesting" items >> len(EnumClass) -> number of members >> member in EnumClass -> True or False >> >> - protection from adding, deleting, and changing members >> - guards against reusing the same name twice >> - possible to have properties and members with the same name (i.e. "value" >> and "name") > > In current Python this is true. But if we would go down the route of > PEP 560 (which I just found, I wasn't involved in its discussion), > then we could just add all the needed functionality to classes. > > I would do it slightly different than proposed in PEP 560: > classmethods are very similar to methods on a metaclass. They are just > not called by the special method machinery. I propose that the > following is possible: > >>>> class Spam: > ... @classmethod > ... def __getitem__(self, item): > ... return "Ham" > >>>> Spam[3] > Ham > > this should solve most of your usecases.
Except when you want to implement __getitem__ for instances as well :-). An important difference between @classmethod and methods on the metaclass is that @classmethod methods live in the same namespace as instance methods, while methods on the metaclass don’t. I ran into similar problems in PyObjC: Apple’s Cocoa libraries use instance and class methods with the same name. That when using methods on a metaclass, but not when using something similar to @classmethod. Because of this PyObjC is a heavy user of metaclasses (generated from C for additional fun). A major disadvantage of this is that tends to confuse smart editors. Ronald _______________________________________________ Python-Dev mailing list Python-Dev@python.org https://mail.python.org/mailman/listinfo/python-dev Unsubscribe: https://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com
