> On Sep 10, 2015, at 3:23 AM, Maciej Fijalkowski <fij...@gmail.com> wrote: > > I would like to know what are the semantics if you subclass something > from itertools (e.g. islice). > > Right now it's allowed and people do it, which is why the > documentation is incorrect. It states "equivalent to: a function-or a > generator", but you can't subclass whatever it is equivalent to, which > is why in PyPy we're unable to make it work in pure python. > > I would like some clarification on that.
The docs should say "roughly equivalent to" not "exactly equivalent to". The intended purpose of the examples in the itertools docs is to use pure python code to help people better understand each tool. It is not is intended to dictate that tool x is a generator or is a function. 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). The description as a function was perhaps used too loosely (in much the same way that we tend to think of int(3.14) as being a function when int is really a class). I tend to think about mapping, filtering, accumulating, as being functions while at the same time knowing that they are actually classes that produce iterators. The section called "itertools functions" is a misnomer but is also useful because the patterns of documenting functions better fit the itertools and because documenting them as classes suggest that they should each have a list of methods on that class (which doesn't make send because the itertools are each one trick ponies with no aspirations to grow a pool of methods). When I get a chance, I'll go through those docs and make them more precise. Sorry for the ambiguity. Raymond _______________________________________________ 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
