Python bindings using cppyy (was: An update on Python bindings)

Albert Astals Cid aacid at
Sun Jan 14 23:09:57 UTC 2018

El dissabte, 13 de gener de 2018, a les 18:05:45 CET, Shaheed Haque va 
> Thanks to some upstream fixes, I have the cppyy-based bindings for KF5 and
> also Qt5 (see below) showing signs of life. 
> Notes:

This is awesome, i'm really happy we're in a point that framework-by-framework 
is possible and that it all seems to be upstream so it's a "hopefully bigger 
group of people" maintaining it :)

Keep it up!


>    1. The packaging has advanced to the point where I think ECM-based
>    framework-by-framework bindings are a real possibility, with both Py2 and
> Py3. AFAICS, this addresses the main feedback received to date. 2. With
> reference to the remark about tracking dependencies between frameworks,
> apologies for the delayed response as I somehow missed the email. I note
> that the dependencies currently in CMake often seem incomplete. I'll bring
> that to the community separately.
>    3. There is one issue still open upstream (
>> select). However, I don't consider this to be a showstopper...we might even
> be able to live with it as is.
>    4. For me, the jury is still out on PyQt versus a new set of cppyy-based
>    Qt bindings. Clearly PyQt is solid and mature, but the limitations really
> concern me (if anybody wants to know more, I'm happy to discuss, but let's
> do that in another thread please). Now, given that there are examples in
> the wild of interoperating cppyy/cling/ROOT with PyQt, I'm going to
> sidestep this question but am playing with a cppyy-based approach. At this
> point, all of Qt has basic cppyy-based bindings, and the next step is to
> tackle things like finding a way to express the object
>    ownership/destruction rules in a more-or-less systematic way.
>    5. On the P2/P3 question, I'm presently still committed to both P2 and
>    P3. I *have* had a couple of minor occasions where P3-only might have
> been nice *for my code*, but if I do find an issue that tips the balance,
> or I find some serious benefit *for the bindings*, I'll drop P2. One
> possible such benefit would be if I can see a sane way to address PEP484
> type hints.
> To get here, I had to build a subset of the tooling I previously had
> developed for the SIP-based approach. The big difference is the absence of
> any need to support customisation of the generated bindings. I am hopeful
> that in the worst case, there might be some minimal customisation (known as
> Pythonisations in cppyy parlance) such as for #4 above, but nothing like
> the scale needed for SIP.
> The core tooling is not specific to KF5 or KDE or Qt5, and is developed in
> upstream cppyy over on The core tooling is built around
> CMake, notably for the generation phase and the C++ library build.
> The PoC extends the core tooling with Pythonic packaging and installation
> using pip/wheels, also from CMake. As before I would look for help to get
> an ECM equivalent, possibly based on the same approach but perhaps
> including CI and distribution via PyPi.
> Finally, now would be a good time for anybody else who wants to get
> involved to step up, especially as a new job limits my free time.
> Thanks, Shaheed
> P.S. Not to stoke the the P2/P3 wars unnecessarily, but while I know that
> upstream Clang just added P3 support in the clang 5.0 release, current
> Ubuntu only packages it for 2.7.14. So I won't be moving yet...
> On 5 November 2017 at 13:23, Boudewijn Rempt <boud at> wrote:
> > On Sat, 4 Nov 2017, Chris Burel wrote:
> > > I think this is a remarkably short sighted statement. It assumes that
> > 
> > people that would use these bindings have no existing Python codebase at
> > all, and can afford to start a brand new project. The reality is much
> > different.
> > 
> > > Let's take a specific example. I have 6 years experience writing Python
> > 
> > for the visual effects industry. We have a 10 year old Python 2 codebase.
> > We also use an application from Autodesk called Maya. It has been a Qt 4
> > application with Python 2 embedded since 2012. In 2016 they jumped to qt 5
> > and pyside2. Now Autodesk knows that companies have built large codebase
> > around their product that requires Python 2. What would've happened if
> > pyside2 did not support Python 2.7? They'd be stuck either forcing all
> > their customers to move to Python 3 and risk people not wanting the new
> > version of the software, or they'd be prevented from moving to Qt 5.
> > 
> > 
> > You will have to switch to Python 3 by 2019, since that's what the VFX
> > Reference Platform says. If you haven't started on the migration yet,
> > you're very late. And the VFX Refernece Platform is basically Autodesk
> > telling the rest of the industry what to use, including their weird
> > patchset for Qt...
> > 
> > > So no, Python 2 is not dead. Not by a long shot.
> > 
> > For VFX, it will be dead in 2019. See
> > 
> > 
> > --
> > Boudewijn Rempt |,

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