[llvm-dev] Migrate utils/ Python 2 scripts to Python 3

Wed Feb 7 17:03:43 PST 2018

I would like to raise the issue that neither python2 nor python2.7 exist on
Windows. This is making it so that I can no longer directly execute .py
files in the git for windows bash shell. Can we revert all this stuff and
go back to the '#!/usr/bin/env python' that worked?

On Thu, Feb 1, 2018 at 3:39 PM, James Y Knight via llvm-dev <
llvm-dev at lists.llvm.org> wrote:

> Nope.
>
> Regarding "python" potentially pointing to python3:
>
> Arch Linux has done that for years. That unilateral decision on their part
> was widely-decried as a mistake at the time, and spawned the python doc you
> reference saying that shouldn't be done. However, Fedora is now making
> noises about doing the same, in a few years, after driving a change in the
> upstream recommendation. While it's certainly not finalized, I'd fully
> expect this to happen at some point.
>
> https://fedoraproject.org/wiki/FinalizingFedoraSwitchtoPython3
> https://wiki.archlinux.org/index.php/python
>
> And, regarding using "python2" instead of "python2.7":
>
> Since python2.7 is the last-ever python2 version, and also the minimum
> version required by llvm, the name "python2" is false generality.
> Additionally, the "python2" symlink is missing on _many_ systems (not just
> macos). So, the choice of "python2.7" is clearly the better option here.
>
>
>
> On Feb 1, 2018 4:59 PM, "Dimitry Andric" <dimitry at andric.com> wrote:
>
> As mentioned in https://docs.python.org/3/using/unix.html#miscellaneous,
> for Python 3 the shebang line should be:
>
> #!/usr/bin/env python3
>
> For Python 2 the shebang line should probably be:
>
> #!/usr/bin/env python2
>
> but as Python 3 should never install its executable under the name
> "python", you could also let it stay at:
>
> #!/usr/bin/env python
>
> instead.
>
> -Dimitry
>
> On 1 Feb 2018, at 22:47, James Y Knight <jyknight at google.com> wrote:
>
> Sadly, neither the latest version of RedHat (released in 2014), nor the
> latest version of macOS (released in 2017) have any version of python3
> available with the default system. On the other hand, TTBOMK, every system
> that does have python3 available also makes python2.7 also easily available.
>
> LLVM is not a primarily python project, so keeping up with the latest
> features of the language, and making them available for developers of LLVM
> is not terribly interesting (contrast with C++ -- enabling developers of
> LLVM to use new C++ features does have a lot of value). There's also no
> particular reason to think that developers will have already installed the
> latest version of python on their systems, if it takes effort to do so.
>
> Python is used here as a convenient scripting language primarily because
> it is commonly/conveniently available across platforms. Requiring a python
> version which does not have the widespread availability (and without a
> compelling reason to want the higher version, other than that it's newer)
> does not seem to make much sense.
>
> So, ISTM that unfortunately, the decision to require python3 for is still
> premature, even some 10 years after its initial release. (Whether that
> state of the world is ridiculous, or whose fault that is, is irrelevant
> here; anyone who wants to have that discussion can go have it on python-dev
> for the 20000th time.)
>
> That said, I do think it could make sense to prepare llvm for the world in
> which "python" is python3 on some systems. So, I'd propose the following:
> 1. Change all #! lines to say "#!/usr/bin/env python2.7" instead of
> "#!/usr/bin/env python", if they only work with 2.7.
> 2. If someone feels motivated, and if it doesn't make the code obtuse,
> port scripts to work with either version -- and for such scripts, change
> the #! line to say "#!/usr/bin/env python".
>
>
> On Thu, Feb 1, 2018 at 3:05 AM, Dimitry Andric via llvm-dev <
> llvm-dev at lists.llvm.org> wrote:
>
>> You might want to tell that to the Prominent North American Enterprise
>> Linux Vendor that everybody is using... :)
>>
>> -Dimitry
>>
>> > On 1 Feb 2018, at 06:28, Tim Northover via llvm-dev <
>> llvm-dev at lists.llvm.org> wrote:
>> >
>> > Since we seem to be voting, I'll -1 it. It's pretty ridiculous to have
>> > a system without Python 3 in 2018 and anyone supplying such a
>> > monstrosity should be encouraged to stop it.
>> >
>> > Tim.
>> >
>> > On 1 February 2018 at 05:20, Philip Reames via llvm-dev
>> > <llvm-dev at lists.llvm.org> wrote:
>> >> +1 to what Chris and Justin said.
>> >>
>> >> I see no strong benefit to moving to python3 and substantial costs.
>> >>
>> >> Philip
>> >>
>> >>
>> >> On 01/30/2018 11:20 AM, Chris Matthews via llvm-dev wrote:
>> >>
>> >> Personally, every machine I work with only has Python 2.7.
>> >>
>> >> Justin is correct that there is a non-trivial amount of effort to
>> convert
>> >> the bots.
>> >>
>> >> Python 3 is wonderful. But, a Python 3 dependency seems like one
>> burden that
>> >> could be avoided.  We have already made that trade-off in the past, for
>> >> example by only using standard python packages, so there is
>> less/nothing to
>> >> pip install when getting started.  Dependencies likes host compiler and
>> >> cmake totally make sense given they are central to how LLVM is made.  I
>> >> don’t think the same for the python code.
>> >>
>> >> I’m in favor of 2/3 compatibility until the death clock ends.
>> >>
>> >> On Jan 30, 2018, at 4:48 AM, 陳韋任 via llvm-dev <llvm-dev at lists.llvm.org
>> >
>> >> wrote:
>> >>
>> >> Does Python 3 have feature we want to use in LLVM codebase, and no
>> >> workaround there? If so, please give some examples. I think that makes
>> the
>> >> discussion more concrete.
>> >>
>> >> 2018-01-30 4:46 GMT+08:00 Fāng-ruì Sòng via llvm-dev
>> >> <llvm-dev at lists.llvm.org>:
>> >>>
>> >>> Hi LLVM-Devs,
>> >>>
>> >>> I noticed that many Python scripts under utils/ have a shebang of
>> >>> `#!/usr/bin/python` (which is a symlink to python2.7 on many
>> platforms)
>> >>> and some of them use Python 2 syntax that is not compatible with
>> Python 3
>> >>> (e.g. print statements; str/bytes)
>> >>>
>> >>> I created a revision to migrate utils/update_{llc_,}_test_checks.py
>> from
>> >>> Python 2 to Python 3 https://reviews.llvm.org/D42450 , the arguments
>> against
>> >>> making it Python 3 is:
>> >>>
>> >>> * There are many Mac OS X users and Mac OS X 10.8 comes with Python
>> 2.7
>> >>> pre-installed [0] but not Python 3.
>> >>> * Forcing scripts to use Python 3 (by doing so we can avoid some
>> >>> compatibility trouble) may not be a good idea.
>> >>>
>> >>> Python 2.7 was published in 2010 and planned as the last of the 2.x
>> >>> releases. It will not be maintained past 2020 and there is also a
>> retirement
>> >>> page https://pythonclock.org/ .
>> >>>
>> >>> The second argument would not need to be addressed if the first one
>> did
>> >>> not lay too much burden on developers. After all, we have to install
>> `cmake,
>> >>> ninja/GNU Make / libedit(for lldb)` to build LLVM. These packages are
>> not
>> >>> installed by default on many platforms.
>> >>>
>> >>> Thoughts on deprecating Python 2 for utils/ scripts (different from
>> >>> libclang or lldb scripts) which are not user-facing?
>> >>>
>> >>> [0]:
>> >>> https://docs.python.org/3/using/mac.html#getting-and-install
>> ing-macpython
>> >>>
>> >>>
>> >>> Thanks,
>> >>> Fangrui
>> >>> _______________________________________________
>> >>> LLVM Developers mailing list
>> >>> llvm-dev at lists.llvm.org
>> >>> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>> >>
>> >>
>> >>
>> >>
>> >> --
>> >> Wei-Ren Chen (陳韋任)
>> >> Homepage: https://people.cs.nctu.edu.tw/~chenwj
>> >> _______________________________________________
>> >> LLVM Developers mailing list
>> >> llvm-dev at lists.llvm.org
>> >> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>> >>
>> >>
>> >>
>> >>
>> >> _______________________________________________
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>> >> llvm-dev at lists.llvm.org
>> >> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>> >>
>> >>
>> >>
>> >> _______________________________________________
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>> >>
>> > _______________________________________________
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>>
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