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Groups > comp.lang.python > #64041
| References | <52d5e408$0$29970$c3e8da3$5496439d@news.astraweb.com> |
|---|---|
| Date | 2014-01-15 19:50 -0500 |
| Subject | Re: Chanelling Guido - dict subclasses |
| From | Daniel da Silva <var.mail.daniel@gmail.com> |
| Newsgroups | comp.lang.python |
| Message-ID | <mailman.5562.1389840613.18130.python-list@python.org> (permalink) |
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On Tue, Jan 14, 2014 at 8:27 PM, Steven D'Aprano < steve+comp.lang.python@pearwood.info> wrote: > > But reading Guido, I think he's saying that wouldn't be a good idea. I > don't get it -- it's not a violation of the Liskov Substitution > Principle, because it's more restrictive, not less. What am I missing? > Just to be pedantic, this *is* a violation of the Liskov Substution Principle. According to Wikipedia, the principle states: if S is a subtype <http://en.wikipedia.org/wiki/Subtype> of T, then > objects of type <http://en.wikipedia.org/wiki/Datatype> T may be replaced > with objects of type S (i.e., objects of type S may be *substituted* for > objects of type T) without altering any of the desirable properties of that > program (correctness, task performed, etc.) [0]<http://en.wikipedia.org/wiki/Liskov_substitution_principle> Since S (TextOnlyDict) is more restrictive, it cannot be replaced for T (dict) because the program may be using non-string keys. Daniel
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Chanelling Guido - dict subclasses Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-01-15 01:27 +0000
Re: Chanelling Guido - dict subclasses Ned Batchelder <ned@nedbatchelder.com> - 2014-01-14 21:04 -0500
Re: Chanelling Guido - dict subclasses Terry Reedy <tjreedy@udel.edu> - 2014-01-14 22:48 -0500
Re: Chanelling Guido - dict subclasses F <f@hop2it.be> - 2014-01-15 07:00 +0000
Re: Chanelling Guido - dict subclasses Peter Otten <__peter__@web.de> - 2014-01-15 09:40 +0100
Re: Chanelling Guido - dict subclasses John Ladasky <john_ladasky@sbcglobal.net> - 2014-01-15 08:51 -0800
Re: Chanelling Guido - dict subclasses Peter Otten <__peter__@web.de> - 2014-01-15 19:35 +0100
Re: Chanelling Guido - dict subclasses Devin Jeanpierre <jeanpierreda@gmail.com> - 2014-01-15 22:30 -0800
Re: Chanelling Guido - dict subclasses Mark Lawrence <breamoreboy@yahoo.co.uk> - 2014-01-15 09:10 +0000
Re: Chanelling Guido - dict subclasses Tim Chase <python.list@tim.thechases.com> - 2014-01-15 05:03 -0600
Re: Chanelling Guido - dict subclasses Daniel da Silva <var.mail.daniel@gmail.com> - 2014-01-15 19:50 -0500
Re: Chanelling Guido - dict subclasses Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2014-01-16 17:17 +1300
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