On Thu, Feb 12, 2015 at 11:01 PM, Guido van Rossum <gu...@python.org> wrote:
> >> 2) always use the type of self when creating new instances >> .. >> cons: >> - if constructor signatures change, must override all methods which >> create new objects >> > > Con for #2 is a showstopper. Forget about it. > Sorry if I am missing something obvious, but I still don't understand why the same logic does not apply to class methods that create new instances: >>> from datetime import * >>> date.today() datetime.date(2015, 2, 13) >>> datetime.today() datetime.datetime(2015, 2, 13, 11, 37, 23, 678680) >>> class Date(date): ... pass ... >>> Date.today() Date(2015, 2, 13) (I actually find datetime.today() returning a datetime rather than a date a questionable design decision, but probably the datetime type should not have been a subclass of the date to begin with.) Are there any date subclasses in the wild that don't accept year, month, day in the constructor? If you create such a class, wouldn't you want to override __add__ and friends anyways? We already know that you will have to override today().
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