On Thu, Sep 5, 2019 at 7:08 PM Andrew Barnert via Python-ideas <python-ideas@python.org> wrote: > > On Sep 4, 2019, at 20:51, Inada Naoki <songofaca...@gmail.com> wrote: > > >> And you’re right, because int|str _looks_ better than (int, str) here, > >> many people will be encouraged to use it even though it’s slower, which > >> could potentially be a bad thing for some programs. > > > > That's exactly my point. If we say "you can use `isinstance(x, int | > > str)` for now", people > > may think it is a new and recommended way to write it. > > Right; I was agreeing, and saying it may even be worse than you’re > suggesting. There’s always the possibility that any shiny new feature looks > like the One True Way and gets overused. But in this case, it looks more > obviously right even to someone who’s not interested in shiny new features > and has never heard the word “pythonic” or read a new version’s release > notes. So they’re going to use it. Which means if they run into a situation > where they’re checking types of a zillion objects, they’re definitely not > going to guess that it’s 5x as slow, so there definitely going to misuse it. >
Hang on hang on.... what's this situation where you're checking types of a zillion objects? I think there's a bigger problem there than whether isinstance(x, int|str) is slower than isinstance(x, (int,str)) ! Even if this change DOES have a measurable impact on the time to do those checks, it only applies to unions, and if that's a notable proportion of your total run time, maybe there's a better way to architect this. The only situation I can think of would be exception handling. As a special case, BaseException could perhaps have an __or__ method that returns a tuple, but even there, I'd want to see a macrobenchmark that shows that the difference actually affects a larger program (especially since most exception checks are by hierarchy, not by union). ChrisA _______________________________________________ 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/VNBDJPQDY767LMBUHFBJYMZ55HJWU5DG/ Code of Conduct: http://python.org/psf/codeofconduct/
