On Mon, 18 Nov 2019 at 14:07, Soni L. <fakedme...@gmail.com> wrote:
> On 2019-11-18 11:32 a.m., Oscar Benjamin wrote:
> > On Mon, 18 Nov 2019 at 13:12, Soni L. <fakedme...@gmail.com> wrote:
> > >
> > > On 2019-11-18 9:10 a.m., Oscar Benjamin wrote:
> > > >
> > > > with nested(open(filename) for filename in filenames) as files:
> > > > ...
> > > >
> > > > Here nested could take advantage of the delayed evaluation in the
> > > > generator expression to invoke the __enter__ methods and call __exit__
> > > > on the opened files if any of the open calls fails. This would also
> > > > leave a "trap" though since using a list comprehension would suffer
> > > > the same problem as if nested took *args:
> > > >
> > > > with nested([open(filename) for filename in filenames]) as files:
> > > > ...
> > >
> > > If generator expressions (aka "(open(filename) for filename in
> > > filenames)") had __enter__ and __exit__ that deferred to inner __enter__
> > > and __exit__, this "trap" wouldn't exist:
> > >
[snip]
> >
> > Since generators already have a close method the obvious thing for
> > generator.__exit__ to do (if it existed) would be to call that. That
> > would make it possible to use patterns like:
> >
[snip]
>
> Sure. We can always split generator methods and generator expressions.
> After all, you can't use "with" in a generator expression, so it makes
> no sense to call close there.
I don't think that splitting these is a good idea. Currently both of
these return the same type of object: a generator. The generator
expression
gen = (x for x in y if z)
is explicitly defined as being equivalent to
def _tmp():
for x in y:
if z:
yield x
gen = _tmp()
The resulting objects are the same and have the same methods etc.
--
Oscar
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