On Wed, Nov 13, 2019 at 11:26 AM MRAB <python@mrabarnett.plus.com> wrote:
     "with" expression ["as" name] ":"

but the expression itself can start with a parenthesis, so if it saw a
parenthesis after the "with" it would be ambiguous

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:
        return True

with opener(
    'x', 'y', 'z'
) as (
    f1,  f2,  f3