Re: [Qemu-devel] [PULL 0/8] Python queue, 2019-06-07

[Eduardo Habkost]

On Tue, Sep 17, 2019 at 03:57:26PM +0200, Kevin Wolf wrote:
> Am 11.06.2019 um 19:12 hat Eduardo Habkost geschrieben:
> > On Tue, Jun 11, 2019 at 05:07:55PM +0100, Peter Maydell wrote:
> > > On Tue, 11 Jun 2019 at 17:03, Eduardo Habkost <address@hidden> wrote:
> > > >
> > > > On Tue, Jun 11, 2019 at 04:50:34PM +0100, Peter Maydell wrote:
> > > > > On Mon, 10 Jun 2019 at 13:58, Peter Maydell <address@hidden> wrote:
> > > > > > Hi. This fails to build on one of my buildtest machines:
> > > > > >
> > > > > > ERROR: Cannot use 'python3', Python 2 >= 2.7 or Python 3 >= 3.5 is 
> > > > > > required.
> > > > > >        Use --python=/path/to/python to specify a supported Python.
> > > > > >
> > > > > > The machine has python 2.7.6 and 3.4.3. (It's an Ubuntu trusty
> > > > > > box; it's one of the gcc compile farm machines so upgrades to its
> > > > > > OS are not really under my control.)
> > > > >
> > > > > Rereading this, I realise that either the check or the error
> > > > > message is wrong here. The machine has 2.7.6, which satisfies
> > > > > "python 2 >= 2.7", so we should be OK to build. The bug
> > > > > seems to be that we say "prefer python3 over plain python
> > > > > on python2" early, but don't revisit that decision if the
> > > > > python3 we found isn't actually good enough for us.
> > > >
> > > > Right.  The error message is technically correct, but misleading.
> > > > python3 is too old, but python2 would work.
> > > >
> > > > We can make configure not use python3 by default if it's too old,
> > > > and fall back to python2 in this case.
> > > 
> > > Sounds good. Since I have now managed to get my alternate
> > > aarch64 box set up, how about I apply this pullreq and you
> > > send a followup patch which does the fallback to python/python2 ?
> > 
> > I will remove the python2/python3 patches and send a new pull
> > request.
> 
> What is the plan forward with this? Are the patches dropped for good?
> 
> I think the plan was to drop Python 2 after QEMU 4.2, and then it
> becomes really relevant what our minimum Python 3 version is. We've just
> had another Python version discussion in the context of iotests (John
> suggested using function annotations, but these are >= 3.5 only).
> 
> Also, the fallback to Python 2 obviously makes no sense any more then,
> so maybe it's not that important to add for a single QEMU release?
> 
> As Peter seems to have indicated above that he found a replacement for
> the test machine with an OS that isn't out of support, can we just
> revive this patch as it is?

My plan is to remove Python 2 support in QEMU 4.2 (making the
fallback to Python 2 a non-issue), and require Python >= 3.5.

Now, even if my plan is rejected and we keep supporting Python 2
when building QEMU 4.2, my suggestion for the iotest maintainers
is to make it require Python 3.5+ immediately, just like we do
for tests/acceptance.  I don't see why we should keep wasting our
energy supporting ancient Python versions in a test suite that is
not a requirement for building QEMU.

-- 
Eduardo