On Thu, Nov 14, 2019 at 8:48 AM Eric Fahlgren <ericfahlgren@gmail.com> wrote:
> I have used 'with' for so long that I was under the impression that the as-target was just a name as in MRAB's simplified syntax above, so imagine my surprise when I tried putting parentheses around the target and didn't get a syntax error straight away.  I of course had to explore a bit, and came up with this.  The ugly formatting of the with is simply to show that the parens behave as expected.
> class opener:
>     def __init__(self, *files):
>         self.files = [open(file) for file in files]
>     def __enter__(self):
>         return [file.__enter__() for file in self.files]
>     def __exit__(self, *exc_info):
>         for file in self.files:
>             file.__exit__(*exc_info)
>         return True
>
> with opener(
>     'x', 'y', 'z'
> ) as (
>     f1,  f2,  f3
> ):
>     print(f1)
>     print(f1.closed)
>     print(f2)
>     print(f3)
>
> print(f1.closed)

Note that the semantics here are NOT the same as the semantics of
either ExitStack or a single large 'with' statement. (And I'm not sure
whether or not those two are the same.) With your opener, you first
open each file, then enter each file; and only then are you considered
to be inside the context. With a large 'with' statement, they should
(I believe) be opened and entered individually. If one of the files
fails to open, your constructor will fail, and self.files won't be set
- you won't exit each of the files that you *did* open.

ChrisA
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