ddtl wrote: > On 7 Sep 2006 10:42:54 -0700, in comp.lang.python you wrote: > > >>Let's examine what the mro order is for class D: >> >>>>>D.mro() >> >>[<class '__main__.D'>, <class '__main__.B'>, <class '__main__.C'>, >><class '__mai >>n__.A'>, <type 'object'>] >> >>When you call d.met(), the call dispatches to the D.met() method. >>After printing out 'D.met', you use super() to get the next class in >>the mro order, and call that class's met method. >> >>As shown with the mro(), the class after D is B. So B.met() is called. >>Normally, we would be done. But take a look at B's method! >> >> >>>class B(A): >>> def met(self): >>> print 'B.met' >>> super(B,self).met() >> >>B.met calls super, and invokes the next met method! So, the code does >>exactly what you've asked it to do, and searches for the next class >>after B in the mro list: class C. > > > But when super(B,self).met() is invoked, isn't it supposed to look > at MRO order of *B*, which is: > > (<class '__main__.B'>, <class '__main__.A'>, <type 'object'>) > No, that's the mistake people often make. An instance of type B would see B's MRO, but an instance of type D sees D's MRO.
> and B doesn't have any relation with C, that is: A's met() is the to > be called as a result. In effect, what you say impies that a call to > super() is context dependant - if super(B,self).met() is invoked as > a result of a call to D().met(), the effect is different from the effect > of a call to B().met(). But a documentation of a super() doesn't mention > anything like that (or at least I didn't find it), and it seems a > significant piece of information. Doesn't it imply that there should > be another explanation? It's all rather better explained in the Nutshell Guide than it is in the Python documentation. But basically you've got it right: it's the class of the *instance* that determines the MRO used by super(). regards Steve -- Steve Holden +44 150 684 7255 +1 800 494 3119 Holden Web LLC/Ltd http://www.holdenweb.com Skype: holdenweb http://holdenweb.blogspot.com Recent Ramblings http://del.icio.us/steve.holden -- http://mail.python.org/mailman/listinfo/python-list
