> I'm not sure why it doesn't special-case it to "".join() One reason might be because you'd have to read the entire iterator to know if it really was only strings. So there are concerns with generators which complicate things a fair bit
On Thu, 17 Jun 2021, 12:12 am Chris Angelico, <ros...@gmail.com> wrote: > On Thu, Jun 17, 2021 at 9:04 AM Christopher Barker <python...@gmail.com> > wrote: > > > > > > >> > >> The performance error for strings should be considered an anomaly, not a > >> feature to be extended to anything that could be used, or misused, with > >> non-linear behaviour. > > > > > > I’m pretty sure that using sum with strings was a real issue in real > code before it was disallowed. > > > > But the irony is that strings in the cPython interpreter have an > optimization that makes it actually work fine :-( > > That *can* make it work. It doesn't always. There are limitations on > the optimization. > > > I’d rather remove the error for strings than add more Type limitations. > > > > I'm not sure why it doesn't special-case it to "".join() instead of > erroring out, but presumably there's a good reason. Given that it > can't easily be done in a cross-interpreter efficient way, it's better > to have people do things in the reliable way rather than depend on a > CPython implementation detail. For instance, this code will probably > work in CPython: > > def modify_file(fn): > data = open(fn).read() > mutate(data) > open(fn, "w").write(data) > > But we don't do that, because it won't be reliable on all interpreters. > > Are *all* Python interpreters going to be required to optimize strings > the way CPython does? If not, it's better to not encourage code to > rely on it. > > 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/3QQSVNJ3DSNQSHNEMJIY6TKX2QDOO7U2/ > Code of Conduct: http://python.org/psf/codeofconduct/ >
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