[Mobile-sig] Progress update on Mobile Python work

Sun Jan 3 16:04:37 EST 2016

Hi Russ,

Thanks for the detailed progress report! I expect that in the next few
years mobile support will become critical for Python, and your work (and
that of others in this area) is much appreciated.

I've got one recommendation: if you feel you're stuck waiting for a core
developer to provide feedback, please don't hesitate to bring the issue up
on python-dev. That's where we're all lurking. (I expect only a very small
number of core devs read mobile-sig.)

Happy 2016,

--Guido

On Sat, Jan 2, 2016 at 7:12 AM, Russell Keith-Magee <russell at keith-magee.com
> wrote:

> Hi all,
>
> This SIG has been a bit quiet of late, but over the last few months (and
> especially over the Christmas/New Year break) I’ve made some significant
> progress on support for Python on mobile platforms (especially Android), so
> I thought I’d give an update of where things (at least, from where I stand).
>
> iOS Support
> ===========
>
> iOS support is getting quite strong. There is a patch against CPython
> 3.4.2 sources:
>
> http://bugs.python.org/issue23670
>
> This patch provides an XCode project that runs the Python test suite.
> There are still a handful of bugs; these are mostly related to edge cases
> in ctypes.
>
> The issues that previously existed with libffi have now been resolved. The
> biggest question with libffi support now is whether there is an opportunity
> to merge libffi support on OS X with the new libffi support on iOS. The
> generated code for libffi_osx is several years old at this point, and it
> would be easy to replace the current libffi_osx generated code with an
> updated version sharing sources with iOS. The only catch is that libffi no
> longer supports PowerPC architectures in their OS X builds (because Apple
> no longer supports those architectures).
>
> There are two impediments currently preventing this patch from being
> merged into trunk.
>
> The first is a bug, reported during the 3.5 alpha, that is still lingering:
>
> http://bugs.python.org/issue22625
>
> This bug was introduced in the process of fixing support for parallel
> builds in the root Makefile. This problem prevents *any* cross platform
> build from working. I don’t have enough Makefile mojo to sort this one out.
>
> The second is the absence of a feedback from someone on the core team. The
> patch really needs a review from someone to indicate which of the design
> decisions I’ve made are acceptable to the CPython core team.
>
> In the meantime, I’ve been maintaining an external project to make it easy
> to build a Python framework for use in an iPhone (or iPad, or AppleTV, or
> Apple Watch) app:
>
> https://github.com/pybee/Python-iOS-support
>
> You can download a pre-compiled version of the libraries from the project
> page. Add an Objective C bridging library (like Rubicon), and you can write
> your iOS (or tvOS) app in Python.
>
> Android Support
> ===============
>
> Cyd Haselton has been working on an analogous patch for CPython to add
> support for Android. From what I can see, he’s having some difficulties;
> the code is segfaulting, and debugging the source of the segfault is
> proving difficult.
>
> I experimented with CPython on Android briefly at the end of 2014; I came
> to the conclusion that it wasn’t really viable, because once you have
> CPython, you need to access Java libraries to actually write an
> application. That means you have to use JNI, and while JNI *exists* on
> Android, it is constrained to the point that it makes writing apps nigh on
> impractical.
>
> Instead, I’ve been working on an alternate approach: transpiling CPython
> 3.4 bytecode directly to Java class files. The result is a project called
> VOC:
>
> https://github.com/pybee/voc
>
> This is a different approach to that used by Jython. There’s no Python
> interpreter at runtime - what
> you push to the phone is a pure Java class file implementing Python
> language semantics. The price you pay is that there’s no exec(), eval() or
> REPL - but if you’re writing an app for distribution on a phone, that
> probably doesn’t matter.
>
> Performance is passable, but not great - PyStone indicates that it’s
> roughly an order of magnitude slower than CPython on the same machine.
> However I haven’t been focussing on performance to date, and there’s a lot
> of low hanging opportunities for optimisation. It’s also worth noting that
> mobile apps (other than games) generally won’t be CPU bound - they’re
> network bound - so this performance issue isn’t as critical as it may seem.
>
> Here’s a sample project:
>
> https://gist.github.com/freakboy3742/3c6b74e8506d47d9bd97
>
> When you compile that code with VOC, you get 3 class files (one for each
> class, and one for the module itself). If you add those class files to an
> Android project and upload to a phone, you get this:
>
> https://twitter.com/PyBeeWare/status/683258762816192513/video/1
>
> There’s still a lot of work to do on VOC; there are some language
> constructs that it doesn’t handle yet (most notably generators and context
> managers), and I need to port the parts of the standard library that are
> written in C. However, as the video shows, even without those parts, you
> can write simple Android applications in Python.
>
> Packaging
> =========
>
> One last thing - I’ve also created project called Briefcase to tie all
> these pieces together.
>
> https://github.com/pybee/briefcase
>
> Briefcase is an extension to distutils that adds setup.py targets to
> package a project for distribution as an app. iOS and OS/X support is quite
> stable. A stub command exists for Android, but it isn’t fully operational
> yet. Apple TV support would be trivial to add - most of the pieces are
> already there, they just need to be tied together.
>
> Summary
> =======
>
> So - that’s where, IMHO, Python on Mobile is at right now.
>
> If you’ve got any questions, comments, or feedback - let me know.
>
> Yours,
> Russ Magee %-)
>
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>
>

-- 
--Guido van Rossum (python.org/~guido)
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