Bugs item #973579, was opened at 2004-06-16 00:43 Message generated for change (Comment added) made by birkenfeld You can respond by visiting: https://sourceforge.net/tracker/?func=detail&atid=105470&aid=973579&group_id=5470
Please note that this message will contain a full copy of the comment thread, including the initial issue submission, for this request, not just the latest update. Category: Documentation Group: None >Status: Closed >Resolution: Duplicate Priority: 5 Submitted By: David MacQuigg (macquigg) Assigned to: Fred L. Drake, Jr. (fdrake) Summary: Doc error on super(cls,self) Initial Comment: In both the Library Reference, section 2.1, and in the Python 2.2 Quick Reference, page 19, the explanation for this function is: super( type[, object-or-type]) Returns the superclass of type. ... This is misleading. I could not get this function to work right until I realized that it is searching the entire MRO, not just the superclasses of 'type'. See comp.lang.python 6/11/04, same subject as above, for further discussion and an example. I think a better explanation would be: super(cls,self).m(arg) Calls method 'm' from a class in the MRO (Method Resolution Order) of 'self'. The selected class is the first one which is above 'cls' in the MRO and which contains 'm'. The 'super' built-in function actually returns not a class, but a 'super' object. This object can be saved, like a bound method, and later used to do a new search of the MRO for a different method to be applied to the saved instance. ---------------------------------------------------------------------- >Comment By: Georg Brandl (birkenfeld) Date: 2006-01-20 18:07 Message: Logged In: YES user_id=1188172 #1163367 suggests a more complete new wording. Closing as duplicate. ---------------------------------------------------------------------- Comment By: David MacQuigg (macquigg) Date: 2004-07-21 17:20 Message: Logged In: YES user_id=676422 While waiting for the perfect solution, would it be possible to have links to this item at the places in the documentation where the corrections should be made (Library Reference 2.1, Quick Reference page 19)? It could save an hour of experimentation for each new user of this feature. ---------------------------------------------------------------------- Comment By: David MacQuigg (macquigg) Date: 2004-06-21 18:23 Message: Logged In: YES user_id=676422 I like the example, but the new explanation still leaves the impression that super() returns a class ( or something that acts like a class). This is what made super() so difficult to figure out the first time I tried it. The 'super' object returned by the function appears to be a collection of references, one to the 'self' instance, and one to each of the classes in the MRO of self above 'cls'. The reason it can't be just a class is that a given super object needs to retrieve a different class each time it is used, depending on what method is provided. The only thing lacking in the example is motivation for why we need super(B,self).meth(arg) instead of just calling C.meth (self,arg). I have a longer example and some motivation on page 16 in my OOP chapter at http://ece.arizona.edu/~edatools/Python/PythonOOP.doc but that may be too long if what we need here is a "man page" explanation. ---------------------------------------------------------------------- Comment By: Jim Jewett (jimjjewett) Date: 2004-06-21 16:50 Message: Logged In: YES user_id=764593 Would an expanded example also help? I'm not sure I like my own wording yet, but ... I propose it as a straw man. """super returns the next parent class[1] class A(object): pass class B(A): def meth(self, arg): super(B, self).meth(arg) class C(A): pass class D(B, C): pass d=D() d.meth() In this case, the super(B, self) call will actually return a reference to class C. Class C is not a parent of class B, but it is the next parent for this particular instance d of class B. [1] Actually, a super class mimicing the parent class. """ ---------------------------------------------------------------------- You can respond by visiting: https://sourceforge.net/tracker/?func=detail&atid=105470&aid=973579&group_id=5470 _______________________________________________ Python-bugs-list mailing list Unsubscribe: http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
