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
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