Re: [Qemu-devel] [Qemu-block] [PATCH] tests: Fix Python 3 detection on older GNU make versions

[Max Reitz]

On 08.11.18 13:43, Markus Armbruster wrote:
> Philippe Mathieu-Daudé <address@hidden> writes:
> 
>> Hi Markus,
>>
>>
>> Le jeu. 8 nov. 2018 09:46, Markus Armbruster <address@hidden> a écrit :
>>
>>> Cleber Rosa <address@hidden> writes:
>>>
>>>> On 11/7/18 1:05 AM, Markus Armbruster wrote:
> [...]
>>>>> PEP 394 recommends software distributions install Python 3 into the
>>>>> default path as python3, and users use that instead of python, except
>>>>> for programs that are source compatible with both 2 and 3.  So, is
>>>>> finding out whether python is a Python 3 really appropriate?  Why can't
>>>>> we just use python3 and be done with it?
>>>>>
>>>>
>>>> I mentioned that before, when you pointed out the issue you fix here,
>>>> that configure may be the best place to get the Python version (not only
>>>> the major version) and make it available elsewhere.  Even if not used
>>>> for other purposes, it is IMO important information to show on the
>>>> resulting "configure" output.
>>>>
>>>> I'm sending patches to do that in a few.
>>>>
>>>>> If we can't: isn't this a configure problem?
>>>>>
>>>>
>>>> I believe adhering to PEP394 is a good thing, but even that document
>>>> recognizes that the real world is not a perfect place: "however, end
>>>> users should be aware that python refers to python3 on at least Arch
>>>> Linux".  And it only covers *nix systems, so if we hope to care for
>>>> non-*nix systems, we have to check the Python version manually.
>>>>
>>>> So, I guess the safest approach from QEMU's side is to check for the
>>>> version indeed.
>>>
>>> If somebody can point to a system people still use where python3 doesn't
>>> get you a Python 3, but python does, catering for such (crappy) systems
>>> in configure makes sense.  Until then, it's a waste of brain waves and
>>> configure run time.
>>>
>>> PEP 394 mentions Arch Linux.  It's been seven years.  What's the most
>>> recent version of Arch Linux that's still crappy in this regard?
>>>
>>
>> Arch doesn't provide python2 by default, thus python points to python3.
> 
> That's non-crappy as long as python3 also exists, as PEP 394 recommends.
> Does it?

Sure it does.

Arch is just problematic in how it handles "python" itself.  I don't
think there is any system that has Python 3 but no "python3".

Max