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SubjectRe: [PATCH 06/14] kbuild: define PYTHON2 and PYTHON3 variables instead of PYTHON
2018-02-06 18:34 GMT+09:00 Greg Kroah-Hartman <gregkh@linuxfoundation.org>:
> On Tue, Feb 06, 2018 at 09:34:46AM +0900, Masahiro Yamada wrote:
>> The variable 'PYTHON' allows users to specify a proper executable
>> name in case the default 'python' does not work. However, this does
>> not address the case where both Python 2 and Python 3 scripts are
>> used in one system.
>>
>> PEP 394 (https://www.python.org/dev/peps/pep-0394/) provides a
>> convention for Python scripts portability. Here is a quotation:
>>
>> In order to tolerate differences across platforms, all new code
>> that needs to invoke the Python interpreter should not specify
>> 'python', but rather should specify either 'python2' or 'python3'.
>> This distinction should be made in shebangs, when invoking from a
>> shell script, when invoking via the system() call, or when invoking
>> in any other context.
>>
>> arch/ia64/scripts/unwcheck.py is apparently written in Python 2, so
>> it should be invoked by 'python2'.
>>
>> It is legitimate to use 'python' for scripts compatible with both
>> Python 2 and Python 3, but this is rare (at least I do not see the
>> case in kernel tree). You do not need to make efforts to write your
>> scripts in that way. Anyway, Python 2 will retire in 2020.
>>
>> This commit is needed for my new scripts written in Python 3.
>>
>> Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
>> ---
>>
>> Makefile | 5 +++--
>> arch/ia64/Makefile | 2 +-
>> 2 files changed, 4 insertions(+), 3 deletions(-)
>>
>> diff --git a/Makefile b/Makefile
>> index 11aff0f..c4e935c 100644
>> --- a/Makefile
>> +++ b/Makefile
>> @@ -384,7 +384,8 @@ GENKSYMS = scripts/genksyms/genksyms
>> INSTALLKERNEL := installkernel
>> DEPMOD = /sbin/depmod
>> PERL = perl
>> -PYTHON = python
>> +PYTHON2 = python2
>> +PYTHON3 = python3
>
> Is this going to break any systems that were previous setting PYTHON?
>
> I like this change, and feel it is the correct thing to do, but having a
> "fallback" might be needed here.
>
> Could you do what the perf makefile does and do something like:
> override PYTHON := $(call get-executable-or-default,PYTHON,$(PYTHON2))
> or is it really not an issue as only ia64 seems to care about this?
>

As far as I see, ia64 is the only instance that has used this ever.

(the perf Makefile defines PYTHON by itself, so should not be a problem.)


If people expect the backward-compatibility for this, I can do like follows:

# backward compatibility for 'PYTHON'
PYTHON2 := $(if $(PYTHON), $(PYTHON), python2)



Another (unlikely) possible breakage is
'python2' may not be installed on users' system.

I believe this is rare, but if needed, I could do like follows
at the cost of ugliness.


PYTHON2 := $(if $(PYTHON), $(PYTHON), \
$(shell python2 --version 2>/dev/null && echo python2 || echo python))



--
Best Regards
Masahiro Yamada

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