Fwiw, I usually don't do
def foo():
if False: yield None
But simply:
def foo():
return ()
That the returned iterable is not a generator seldom matters.
Stephan
Op wo 22 aug. 2018 21:17 schreef Chris Angelico <ros...@gmail.com>:
> On Thu, Aug 23, 2018 at 3:56 AM, Rhodri James <rho...@kynesim.co.uk>
> wrote:
> > On 22/08/18 14:38, Jonathan Fine wrote:
> >>>>> def fn():
> >>
> >> ... if None:
> >> ... yield
> >> ...
> >>>>>
> >>>>> list(fn()) # Fails, unless fn is a generator function.
> >>
> >> []
>
> Actually, it fails unless fn returns some sort of iterable.
>
> >> I think what's happening is this. Even though the None-guarded yield
> >> has been optimised away, it leaves a residue. Namely, that there's a
> >> yield in the function. Hence fn() is an iterator.
> >>
> >> Having explained the surprise, here's how it can help you. Suppose you
> >> have a long function body, with a single yield at the bottom. If you
> >> write like this:
> >>
> >> def my_very_long_function_with_one_yield_point(...):
> >> if None: yield # This is a generator function.
> >>
> >> then the next programmer can know immediately that it's a generator
> >> function.
> >
> >
> > Ew.
> >
> > I'd prefer this way of doing it:
> >
> > def my_very_long_function_with_one_yield_point(...):
> > # This is a generator
> >
>
> Or you could use a return type annotation.
>
> Why should generator objects be special? A generator function is very
> similar to a function that returns a list, except that it can yield
> values as it gets them, rather than batching them up to the end. A
> generator function is a function which returns an iterable object of
> the type "generator". How is it different from a function that returns
> an integer? They return different things. How do you show what a
> function returns? You annotate it, put it in the docstring, put it in
> external docs... It's a function. It does something, it returns
> something. That's it.
>
> ChrisA
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