On Fri, Jan 25, 2013 at 10:40 AM, lars van gemerden <l...@rational-it.com> wrote: > Hi all, > > i was writing a function to determine the common base class of a number > classes: > [...] > > and ran common_base(int, float), hoping to get numbers.Number. > > this did not work because abstract base classes are not always in the mro() > of classes. > > My question is: is there a way to obtain the abc's of a class or otherwise a > way to make the function above take abc's into account (maybe via a > predefined function)?
If the abstract base class's module has not been imported, it may not even be loaded into memory, even though it is technically considered a superclass. Consider this: Python 2.7.1 (r271:86832, Nov 27 2010, 18:30:46) [MSC v.1500 32 bit (Intel)] on win32 Type "help", "copyright", "credits" or "license" for more information. >>> def common_base(classes): ... common = set() ... for cls in object.__subclasses__(): ... if all(issubclass(c, cls) for c in classes): ... common.add(cls) ... return common ... >>> common_base([int, float]) set([<class '_abcoll.Hashable'>]) >>> import numbers >>> common_base([int, float]) set([<class 'numbers.Number'>, <class '_abcoll.Hashable'>]) If you're okay with that, then the approach above might work. > while len(common) > 1: > cls1 = common.pop() > cls2 = common.pop() > if issubclass(cls1, cls2): > common.add(cls1) > elif issubclass(cls2, cls1): > common.add(cls2) There is a flaw with your set reduction code here. If neither class is a subclass of the other, then both will be removed. There may not actually be a single closest common base class, however. What would you expect the function to return in the following situation? class A(object): pass class B(object): pass class C(A, B): pass class D(A, B): pass print common_base([C, D]) -- http://mail.python.org/mailman/listinfo/python-list
