On Fri, Mar 12, 2021 at 8:20 AM Serhiy Storchaka <storch...@gmail.com> wrote: > > 01.03.21 23:59, Cameron Simpson пише: > > On 28Feb2021 23:47, Alan Gauld <alan.ga...@yahoo.co.uk> wrote: > >> On 28/02/2021 00:17, Cameron Simpson wrote: > >>> BUT... It also has a __iter__ value, which like any Box iterates over > >>> the subboxes. For MDAT that is implemented like this: > >>> > >>> def __iter__(self): > >>> yield from () > >> > >> Sorry, a bit OT but I'm curious. I haven't seen > >> this before: > >> > >> yield from () > >> > >> What is it doing? > >> What do the () represent in this context? > > > > It's an empty tuple. The yield from iterates over the tuple, yielding > > zero times. There are shorter ways to write that (eg outright omitting > > the yield), except when you're writing a generator function with only a > > single yield statement - then you need something like that to make it a > > generator. > > I was wondering what from following variants is more efficient: > > def gen1(): > yield from () > > def gen2(): > return > yield > > def gen3(): > return iter(()) > > > $ python3.9 -m timeit -s 'def g(): yield from ()' 'list(g())' > 1000000 loops, best of 5: 266 nsec per loop > $ python3.9 -m timeit -s 'def g():' -s ' return' -s ' yield' 'list(g())' > 1000000 loops, best of 5: 219 nsec per loop > $ python3.9 -m timeit -s 'def g(): return iter(())' 'list(g())' > 2000000 loops, best of 5: 192 nsec per loop >
They're not identical. The first two are, I believe, equivalent (and you could add "if False: yield" as another comparison if you care), but the third one isn't a generator. So if all you need is an iterator, sure, but gen3 actually isn't doing as much as the other two are. ChrisA -- https://mail.python.org/mailman/listinfo/python-list
