On Sun, Sep 13, 2015 at 5:46 PM, Raymond Hettinger <raymond.hettin...@gmail.com> wrote: > >> On Sep 13, 2015, at 3:49 AM, Maciej Fijalkowski <fij...@gmail.com> wrote: >> >>> The intended semantics are that the itertools are classes (not functions >>> and not generators). They are intended to be sub-classable (that is >>> why they have Py_TPFLAGS_BASETYPE defined). >> >> Ok, so what's completely missing from the documentation is what *are* >> the semantics of subclasses of those classes? Can you override any >> magic methods? Can you override next (which is or isn't a magic method >> depending how you look)? Etc. >> >> The documentation on this is completely missing and it's left guessing >> with "whatever cpython happens to be doing". > > The reason it is underspecified is that this avenue of development was > never explored (not thought about, planned, used, tested, or documented). > IIRC, the entire decision process for having Py_TPFLAGS_BASETYPE > boiled down to a single question: Was there any reason to close this > door and make the itertools not subclassable? > > For something like NoneType, there was a reason to be unsubclassable; > otherwise, the default choice was to give users maximum flexibility > (the itertools were intended to be a generic set of building blocks, > forming what Guido termed an "iterator algebra"). > > As an implementor of another version of Python, you are reasonably > asking the question, what is the specification for subclassing semantics? > The answer is somewhat unsatisfying -- I don't know because I've > never thought about it. As far as I can tell, this question has never > come up in the 13 years of itertools existence and you may be the > first person to have ever cared about this. > > > Raymond
Well, fair enough, but the semantics of "whatever happens to happen because we decided subclassing is a cool idea" is possibly the worst answer to those questions. Ideally, make it non-subclassable. If you want to have it subclassable, then please have defined semantics as opposed to undefined. _______________________________________________ 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/archive%40mail-archive.com
