The below code worked on Python 3.5, 3.6, 3.7, and 3.8, but it now crashes on Python 3.9.


from contextlib import contextmanager


@contextmanager
def open_files(names):
    yield names  # This would actually return file objects


with open_files(['file1.txt', 'file2.txt']) as (first, *rest):
    print(first, rest)


The error shown is:

    with open_files(['file1.txt', 'file2.txt']) as (first, *rest):
                                                                 ^
SyntaxError: invalid syntax

This is a duplicate of issue bpo-41979, which was already fixed in this merged PR https://github.com/python/cpython/pull/22611 and backported to 3.9.

The example code does not error on the latest 3.10. I'm guessing that the bugfix will come in 3.9.1 since the fix wasn't able to make it into 3.9.0.

Already fixed with GH-22612