On Mon, 2009-08-17 at 20:27 +0100, Alan Gauld wrote: > > way I could enforce behaviours like "not null" or "default" from within > > the datastructure itself (for example in the __init__ method) rather > > than enforcing a logic from outside (i.e. the "mother class"). > > But those features are features of the record not of the table. > A table is simply a collection of records. Most of the functionality > should be in the record, the table should only need to insert,delete, > search, sort etc. And those methods should be written to use > polymorphism to be record independent
I suppose one of us is missing the point of the other one, as it looks to me that we are saying the same. :) I would indeed enforce those checks and defaults in the child class (i.e. nested) so that the mother class can have "generic methods" that would work with various records. Indeed - if I truly wished to use nested classes - I would probably define certain module-wide "generic" classes for both "tables" and "records" and then I would subclass them in hierarchic form, so that the class TableA(Table) has a nested class RecordA(Record). I would think of that as a legitimate design with strong encapsulation. Again though... I am not advocating for this method as "the best one", I am just try to imagine a "rationale for nested classes" as per request of the OP. > > I believe classes/objects are also the most elegant way to implement > > singletons, so maybe if you need a singleton for each object generated > > with the "mother class", maybe that is also an occasion in which a > > subclass comes handy. > > I have no idea what you mean by that bit. Classes can be used for > singletons but I don;t see where nested classes come into it. Mmmm... giving a second thought to it, what I had in mind can be achieved with a single class. So apologies, disregard this bit! :) > > would be very happy if any of the tutors would comment on what above, > > even if it is for disagree with it! :) > > Be very happy! :-) > More seriously, I suspect from your comments that you too are > getting confused about the difference between inheritance and nesting. > nesting is about hiding the class name and definition. Inheritance is > about subclassing. They are very different concepts. Nesting tends > to make subclassing more difficult (albeit in Python only trivially so) Well, thank you for the feedback indeed. I am one of those people who get their mind clear only when they interact with others. As for the confusion between nesting and inheritance... no, I think I have that one pretty well under my belt. :) Thank you again, Mac. _______________________________________________ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
