llvm dev - Jan 2020 - [RFC] Python 2 / Python 3 status

On 2020-01-29, Reid Kleckner via llvm-dev wrote:
>On Wed, Jan 29, 2020 at 2:27 AM Serge Guelton via llvm-dev <
>llvm-dev at lists.llvm.org> wrote:
>
>> My personal take on this would be to start moving forward. Still
>> supporting both
>> version this year, but obsoleting Python 2.7 and requiring, say Python
3.6,
>> starting January 2021 looks like a good compromise.
>>
>
>Sounds good to me. Keeping the window of time during which we support both
>Python 2 and 3 as small as possible would be nice.
One blocker may be shebang, #!/usr/bin/env python

may pick either Python 2 or Python 3, if the distributions haven't
migrated.

Some scripts has dome
`#!/usr/bin/env python` -> `#!/usr/bin/env python3` but some have not.
If we can update the rest, it may be easier for our overall migration.

I also recall Reid said `#!/usr/bin/env python` might make Windows
developers happier but I forget the details.
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On Wed, Jan 29, 2020, 21:30 Fangrui Song via llvm-dev <
llvm-dev at lists.llvm.org> wrote:
> On 2020-01-29, Reid Kleckner via llvm-dev wrote:
> >On Wed, Jan 29, 2020 at 2:27 AM Serge Guelton via llvm-dev <
> >llvm-dev at lists.llvm.org> wrote:
> >
> >> My personal take on this would be to start moving forward. Still
> >> supporting both
> >> version this year, but obsoleting Python 2.7 and requiring, say
Python
> 3.6,
> >> starting January 2021 looks like a good compromise.
> >>
> >
> >Sounds good to me. Keeping the window of time during which we support
both
> >Python 2 and 3 as small as possible would be nice.
>
+1

> I also recall Reid said `#!/usr/bin/env python` might make Windows
> developers happier but I forget the details.
>
Python on windows has a wrapper that parses this line and selects which
python to use bases on that.
>
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On Wed, Jan 29, 2020 at 1:12 PM Tobias Hieta via llvm-dev <
llvm-dev at lists.llvm.org> wrote:
> On Wed, Jan 29, 2020, 21:30 Fangrui Song via llvm-dev <
> llvm-dev at lists.llvm.org> wrote:
>
>> I also recall Reid said `#!/usr/bin/env python` might make Windows
>> developers happier but I forget the details.
>>
>
> Python on windows has a wrapper that parses this line and selects which
> python to use bases on that.
>
I believe many developers develop from the "git bash" msys shell. In
this
context, bash will interpret the shebang line. If the shebang line is
`#!/usr/bin/env python3` and there is no python3.exe on PATH, that will be
an error.

For the Linux distros that are removing Python 2, will "python" find
Python
3 in the future, or will we have to say "python3" explicitly?
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