Re: [Qemu-devel] [RFC] Require Python 3 for building QEMU

[Christian Borntraeger <borntraeger@de.ibm.com>]

On 10/15/2018 06:33 PM, Markus Armbruster wrote:
> Kevin Wolf <kwolf@redhat.com> writes:
> 
>> Am 15.10.2018 um 12:02 hat Peter Maydell geschrieben:
>>> On 15 October 2018 at 10:32, Daniel P. Berrangé <berrange@redhat.com> wrote:
>>>> On Sat, Oct 13, 2018 at 02:02:27AM -0300, Eduardo Habkost wrote:
>>>>> Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
>>>>> ---
>>>>> I'd like to do this in QEMU 3.1.  I think it's time to drop
>>>>> support for old systems that have only Python 2.
>>>>>
>>>>> We still have a few scripts that are not required for building
>>>>> QEMU that still work only with Python 2 (iotests being the most
>>>>> relevant set).  Requiring Python 3 for building QEMU won't
>>>>> prevent people from using those scripts with Python 2 until they
>>>>> are finally ported.
>>>>
>>>> I think it is premature & unecessary to do this. We just got QEMU building
>>>> with dual Python2/3 in 3.0 to give people leeway in the migration path to
>>>> a fully v3 future. The code to support building 2/3 in parallel is not
>>>> imposing a unreasonable maint burden. Dropping py2 suport would have
>>>> negligible impact on the code, as there's no v3-only features we have
>>>> used. IOW, I don't think there's a compelling reason to rush into forcing
>>>> users onto v3.
>>>>
>>>> If we want to drop py2, we should give people a warning of such a planned
>>>> change, especially since some of our targetted host OS[1] don't even
>>>> include a py3 as standard without acquiring extra add-on repos. Devs in
>>>> a typical corporate env will not have the freedom to install such extra
>>>> repos on their machines.
>>>
>>> I agree. I also think that dropping python 2 support before we've
>>> even converted all our python scripts to handle python 3 is the
>>> wrong order to do things. People interested in moving forward with
>>> the transition to python-3-only should start by making sure everything
>>> we have works with python 3...
>>
>> It's easier to port stuff to Python 3 though than making them work with
>> both. I think Eduardo's RFC is in part motivated by a patch from
>> Philippe that converted something in iotests to work with Python 3,
>> passed review and then turned out to break Python 2.
> 
> Seconded.  This is not about the cost of maintaining existing
> compatibility gunk, it's about the extra effort to first get the
> remainder to work with 2 and 3, only to throw away 2 a few months later.
> 
> I propose we permit ourselves to port stuff that isn't essential to
> building QEMU straight to 3 instead.  This includes iotests.
> 
>> Having to test every iotests patch twice with different Python versions
>> isn't something I would like to do for extended periods of time.
> 
> It's worth doing only if the benefits of doing it outweigh the costs.  I
> don't think they do.

FWIW, I do not care about python 2 vs 3. I just want to emphasize that I 
consider the qemu iotest a very valuable part of the qemu test suite as it
has detected a lot of regressions over the past years. So as long as we keep
that running I am fine.
>