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

Thu Feb 1 13:47:03 PST 2018

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-
> installing-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
> >>
> >>
> >>
> >>
> >> _______________________________________________
> >> 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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