On Wed, Apr 7, 2021 at 10:01 AM Serhiy Storchaka <storchaka@gmail.com> wrote:

07.04.21 19:13, Victor Stinner пише:
> Hi Inada-san,
>
> I'm +0 on removing again the flag, but I would prefer to not endorse
> the responsibility. I am already responsible for enough incompatible
> changes in Python 3.10 :-D
>
> Some context on this "U" open mode. The flag is accepted by many
> functions opening files. It is deprecated (emit DeprecationWarning)
> for 9 years (Python 3.3, 2012).

It was silently deprecated before 3.3 (perhaps it was no-op since 3.0).

I added DeprecationWarning with intention to remove this option in all
functions accepting it. The only non-trivial support of the "U" mode was
left in ZipFile.open(), and it was broken since beginning.

I think at this point the DeprecationWarning has definitely been on long enough, there was an explicit warning about it in Python 3.9, and 3.10 will be nearly 2 years removed from 2.7 reaching EOL which is the only place where "U" may still be used. So I think it's fine to drop "U" in 3.10.