On Friday, January 25, 2013 8:04:32 PM UTC+1, Ian wrote: > 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])
thanks, good catch, and very concise answer. I'll give up on trying to get abc's and improve my algorithm. -- http://mail.python.org/mailman/listinfo/python-list
