On Fri, May 27, 2011 at 4:37 AM, Steven D'Aprano < steve+comp.lang.pyt...@pearwood.info> wrote:
> On Fri, 27 May 2011 18:49:52 +1000, Ben Finney wrote: > > > Raymond Hettinger <pyt...@rcn.com> writes: > > > >> Hope you enjoyed the post. > > > > I certainly did. > > > > But I'm not better enlightened on why ‘super’ is a good thing. > > Perhaps Raymond assumed that by now everybody knows that multiple > inheritance in Python that doesn't use super is buggy. super() was > introduced in version 2.2 in order to overcome bugs in MI, making it > about 8 years old now. > > (Technically, it's only MI with diamond-shaped inheritance, but that > applies to *all* new-style classes. If you're writing multiple > inheritance in Python 3 without using super, your code is a land-mine > waiting to go off. If you're writing single inheritance, it's *still* a > land-mine, just waiting for some poor caller to use it in a MI context.) > > But I do agree with you in that I expected to see at least some > discussion of why super should be actively preferred over calling the > parent class directly. > > Seems like he does just that for most of the first section. > > > The > > exquisite care that you describe programmers needing to maintain is IMO > > just as much a deterrent as the super-is-harmful essay. > > I don't see that Raymond describes anything needing "exquisite care". > It's more common sense really: ensure that your method signature and that > of your parents' match, plus good work-arounds for when they don't. > Anyone using inheritance is almost certainly 98% of the way there, unless > they're writing classes like this and wondering why they don't work :) > > class MyBrokenList(list): > def __len__(self): > n = list.__len__(self, extra=42) > return n + 1 > def __getitem__(self, i): > return list.__getitem__(self) + 1 > def last_item(self): > return list.last_item(self) + 1 > > > I was thrilled to learn a new trick, popping keyword arguments before > calling super, and wondered why I hadn't thought of that myself. How on > earth did I fail to realise that a kwarg dict was mutable and therefore > you can remove keyword args, or inject new ones in? > > Given the plethora of articles that take a dim, if not outright negative, > view of super, it is good to see one that takes a positive view. Thanks > Raymond! > > +1 -eric > > > -- > Steven > -- > http://mail.python.org/mailman/listinfo/python-list >
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