Maric Michaud wrote: > Le lundi 26 juin 2006 20:06, [EMAIL PROTECTED] a écrit : > > What are the reason one would get this error: TypeError: Cannot create > > a consistent method resolution order (MRO) for bases object ?? > > > > I can provide the code if needed.... > This is the python solution to the diamond problem (cf. wikipedia). > > In [61]: class a(object) : pass > ....: > In [62]: class b(a) : pass > ....: > In [63]: class c(object, a) : pass > ....: > --------------------------------------------------------------------------- > exceptions.TypeError Traceback (most recent > call last) > > /home/maric/<ipython console> > > TypeError: Error when calling the metaclass bases > Cannot create a consistent method resolution > order (MRO) for bases object, a > > In [64]: b.mro() > Out[64]: [<class '__main__.b'>, <class '__main__.a'>, <type 'object'>] > > In [65]: class c(a, object) : pass > ....: > > In [66]: c.mro() > Out[66]: [<class '__main__.c'>, <class '__main__.a'>, <type 'object'>] > > In [67]: class d(b, c) : pass > ....: > > In [69]: d.mro() > Out[69]: > [<class '__main__.d'>, > <class '__main__.b'>, > <class '__main__.c'>, > <class '__main__.a'>, > <type 'object'>] > > mro means "method resolution order", this is the path the interpreter will > look for attributes for a given class. You cannot introduce inconsistency in > this path, for example duplicate the type object before another type (or any > type wich appear to be the ancestor of another). > > --
Ah, thank you Maric, I see the problem. I diagrammed the flow of class inheritance and I can see the problem clearly. Ruby doesn't have this problem because it uses a single inheritance model complemented by the power of mixins (modules of functionality mixed into classes as needed). So what's the Pythonic solution to this problem? -- http://mail.python.org/mailman/listinfo/python-list
