On Wed, Sep 4, 2019 at 1:15 PM Andrew Barnert via Python-ideas <python-ideas@python.org> wrote: > > On Sep 3, 2019, at 19:45, Steven D'Aprano <st...@pearwood.info> wrote: > > > > On Thu, Aug 29, 2019 at 06:20:55PM +0100, Rob Cliffe via Python-ideas wrote: > > > >>> isinstance(x, str | int) ==> "is x an instance of str or int" > >> > >> Er, is that necessary when you can already write > >> isinstance(x, (str, int)) > > > > It's not *necessary* it's just nicer. > > Definitely. It reads even more like what it means than the existing spelling, > and it’s something novices are almost certain to expect to work, and so on. > > But that implies that you can also write this: > > isinstance(x, Union[str, int]) > > … because, after all, str|int is defined as meaning exactly that. Which > implies that the current rule that instantiated genetic types cannot be used > for runtime type checks needs to be changed. > > That’s certainly plausible, and maybe reasonable. But as I understand it, the > idea that there things can’t be used for runtime type checks was a > fundamental guiding principle to the typing design. So, it’s not something to > be changed lightly. Someone has to go back to the reason for that principle > (which may not be clearly stated anywhere, in which case it has to be > extracted from things that _have_ been argued), and then make the case for > why it should be violated here. And I haven’t seen anyone make that case. (If > someone has and I missed it, apologies; chunks of this thread keep getting > flagged as spam for some reason…)
I dislike runtime behavior of static types because I am very afraid accidental large performance or memory footprint regression. ABC has extension module for speedup, but `isinstance([], Iterable)` is 4x slower than `isinstance([], (str, list)`. ``` $ python3 -m pyperf timeit -s 'from collections.abc import Iterable; x=[]' -- 'isinstance(x, Iterable)' ..................... Mean +- std dev: 280 ns +- 8 ns $ python3 -m pyperf timeit -s 'x=[]; T=(str, list)' -- 'isinstance(x, T)' ..................... Mean +- std dev: 73.1 ns +- 1.0 ns ``` Typing module doesn't have speedup extension. I expect`isinstance([], Union[str, list])` will be much slower than `isinstance([], (str, list))`. Regards, -- Inada Naoki <songofaca...@gmail.com> _______________________________________________ Python-ideas mailing list -- python-ideas@python.org To unsubscribe send an email to python-ideas-le...@python.org https://mail.python.org/mailman3/lists/python-ideas.python.org/ Message archived at https://mail.python.org/archives/list/python-ideas@python.org/message/HHIAHG7MLOL2DP5NXK5OCWC5ENKWOAEW/ Code of Conduct: http://python.org/psf/codeofconduct/
