Le lundi 04 septembre 2006 12:25, Mike Krell a écrit : > 1. The super() call in D somehow invokes both parent class methods > instead of stopping when the method is resolved in B. This has > nothing to do with truncated lookup per se. Why isn't the output "D > B A"? >
Yes but, super(B, B()) and super(B,D()) are not the same object like the code below shows. > 2. If I understand correctly, B's MRO is (B, A) and super(B, self) would > have an MRO of (A). Similarly for C. So it seems that by the above > explanation, A.met() would still be invoked twice (assuming both > B.met() and C.met() are invoked). super(class_, self), is an instance of super, so its class, "super", have a mro of [<type 'super'>, <type 'object'>].... "self" in each method call is the same and indeed its type's mro doesn't change ! -- In [80]: class A(object) : ....: def sup(self) : ....: print 'A' ....: ....: In [81]: class B(A) : ....: def sup(self) : ....: print 'B' ....: s(B, self).sup() ....: ....: In [82]: class C(A) : ....: def sup(self) : ....: print 'C' ....: s(C, self).sup() ....: ....: In [83]: class D(B,C) : ....: def sup(self) : ....: print 'D' ....: s(D, self).sup() ....: ....: In [97]: class s(super) : ....: def __new__(*a) : ....: print a ....: return super.__new__(*a) ....: ....: In [98]: D().sup() D (<class '__main__.s'>, <class '__main__.D'>, <__main__.D object at 0xa763186c>) B (<class '__main__.s'>, <class '__main__.B'>, <__main__.D object at 0xa763186c>) <--- instance is always the same !! C (<class '__main__.s'>, <class '__main__.C'>, <__main__.D object at 0xa763186c>) <--- instance is always the same !! A In [100]: super(B, D()).sup() C (<class '__main__.s'>, <class '__main__.C'>, <__main__.D object at 0xa763178c>) A This shows that C is called following the mro of type(D()) from class B to top and not the mro of B. All the magic is in the __getattribute__ of super which retrieve the following class in the mro given its argument. In [140]: class A(object) : .....: def sup(self) : print 'a' .....: .....: In [141]: class B(A) : .....: def sup(self) : print 'b' .....: .....: In [142]: class C(A) : .....: def sup(self) : print 'c' .....: .....: In [143]: class D(B,C) : pass .....: In [147]: super.__getattribute__(super(D,D()), 'sup')() b In [148]: super.__getattribute__(super(B,D()), 'sup')() c In [149]: super.__getattribute__(super(C,D()), 'sup')() a Hope this is clear. _____________ Maric Michaud _____________ Aristote - www.aristote.info 3 place des tapis 69004 Lyon Tel: +33 426 880 097 -- http://mail.python.org/mailman/listinfo/python-list
