Interesting: http://stackoverflow.com/questions/5490824/should-constructors-comply-with-the-liskov-substitution-principle
On Fri, Feb 13, 2015 at 3:37 PM, Isaac Schwabacher <ischwabac...@wisc.edu> wrote: > On 15-02-13, Guido van Rossum wrote: > > Are you willing to wait 10 days for an answer? I'm out of round > tuits for a while. > > IIUC, the argument is that the Liskov Substitution Principle is a > statement about how objects of a subtype behave relative to objects of a > supertype, and it doesn't apply to constructors because they aren't > behaviors of existing objects. So other overriding methods *should* be able > to handle the same inputs that the respective overridden methods do, but > constructors don't need to. Even though __init__ is written as an instance > method, it seems like it's "morally" a part of the class method __new__ > that's only split off for convenience. > > If this message is unclear, it's because I don't really understand this > myself and I'm trying to articulate my best understanding of what's been > said on this thread and those it links to. > > ijs > > > On Fri, Feb 13, 2015 at 10:22 AM, Alexander Belopolsky < > alexander.belopol...@gmail.com(javascript:main.compose()> wrote: > > > > > > > > On Fri, Feb 13, 2015 at 1:19 PM, Alexander Belopolsky < > alexander.belopol...@gmail.com(javascript:main.compose()> wrote: > > > >> > > > >> FWIW you're wrong when you claim that "a constructor is no > different from any other method". Someone else should probably explain this > (it's an old argument that's been thoroughly settled). > > > > > > > > > > > > Well, the best answer I've got in the past [1] was "ask on > python-dev since Guido called the operator overriding expectation." :-) > > > > > > > > > And let me repost this bit of history [1]: > > > > > > Here is the annotated pre-r82065 code: > > > > > > 39876 gvanrossum def __add__(self, other): > > > 39876 gvanrossum if isinstance(other, timedelta): > > > 39928 gvanrossum return self.__class__(self.__days + other.__days, > > > 39876 gvanrossum self.__seconds + other.__seconds, > > > 39876 gvanrossum self.__microseconds + other.__microseconds) > > > 40207 tim_one return NotImplemented > > > 39876 gvanrossum > > > > > > > > > > > > [1] http://bugs.python.org/issue2267#msg125979 > > > > > > > > > > > > > > > > -- > > --Guido van Rossum (python.org/~guido(http://python.org/~guido)) > _______________________________________________ > Python-Dev mailing list > Python-Dev@python.org > https://mail.python.org/mailman/listinfo/python-dev > Unsubscribe: > https://mail.python.org/mailman/options/python-dev/mistersheik%40gmail.com >
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