[Mobile-sig] python on android

Russell Keith-Magee russell at keith-magee.com
Thu Jan 29 05:04:42 CET 2015


Hi Bill,

On Thu, Jan 29, 2015 at 10:41 AM, Bill Janssen <janssen at parc.com> wrote:

> Russell Keith-Magee <russell at keith-magee.com> wrote:
>
> >  b) I don't like the Kivy build tools. They're a lot more complex than
> they
> > need to be.
>
> I didn't find it troublesome, but of course this wasn't my first rodeo.
> I'd certainly agree it's not a push-button solution.  So, what would a
> less complex system be like?
>

A less complex system is what Toga does.

 1. You use cookiecutter to generate a stub project. This gives you the
full source tree for a project you can load into XCode (iOS), or build with
ant (Android), including a "hello world" __main__.py

 2. You download the pre-compiled Python.framework for iOS, or libPython
for Android, and copy it into a libs directory

 3. You start writing Python code, replacing the __main__.py with your own
logic.

 4. You compile and deploy your project using XCode/ant.

Compare this with Kivy - My experience was spending a couple of days
getting the Kivy build process to actually work - trying to find versions
of the Android NDK that aren't being distributed any more (but are the only
hard coded options in the build system), working out that the provided code
doesn't work with the most recent versions of Cython, and sourcing
libraries for all sorts of dependencies, so that I could compile SDL and a
bunch of OpenGL stuff - none of which I needed. It took me a couple of days
to get to "hello world" - and all because of something that could have been
shipped as a pre-compiled binary.


> > I'm going to guess the Kivy people are all Linux users, because
> > they don't appear to have worked out that binary compatibility is a
> thing.
>
> Sorry -- why is that a Linux thing?
>

If I want to distribute an app for OS/X or Windows, I give you an
executable, and It Just Works (tm). Source *might* be provided as an option
in the interest of being open source, but it's not how you distribute
anything in practice. The "Linux way" for distribution is to distribute
source, and tell you to compile it yourself. Distributing binaries is an
afterthought, because ABI compatibility makes building and distributing
binaries painful. Most projects don't have the infrastructure to distribute
binaries for multiple platforms, so unless you can get the OS to provide a
recent binary for you, you compile from source.

I see reflections of that bias here. Even though ABI compatibility exists
for both iOS and Android as platforms, Kivy chooses to distribute as source.


> > You don't need to have every user compile Python and the rest of the Kivy
> > stack - you can just ship a binary library, and it will work on every
> phone
> > with the same hardware (I know, because Toga does this. The Toga
> > bootstrapping process is "clone this repo, and copy this file". You could
> > reduce this to "clone this repo" if you were happy putting binary
> artefacts
> > into version control.)
>
> Sure.
>
> >  c) Kivy's build tools are Python 2.7.1 only on iOS, and 2.7.2 on
> Android;
>
> I believe the mobile platform packaging tools are still stuck at 2.7.
> Kivy 1.8+ will run on Python 3 on desktop, though.


Yes - but in practice, the absence of Python 3 on Mobile means that Kivy on
Mobile is Python 2 only, and an old version at that.


> > and if you build them on OSX, when you're on the device, they report
> > sys.platform as "darwin".
>
> Seems like a bug; I imagine you're suggesting that the Kivy build
> process should patch that file to return "android"?  Although I never
> know what to look at to get that platform info correctly -- this is a
> larger Python issue.
>

Yes, it's a bug (or at least a missing feature). The build system patches
that Kivy use doesn't introduce anything for targeted builds (i.e., using
an x86 platform to compile ARM64 binaries - which is what you're doing when
you compile for mobile), and doesn't provide a platform definition for
mobile.


> And kivy.utils.platform seems to return the proper thing.
>

So... instead of they've introduced their own way to get access to
information that Python already has a standard way of providing.


> > Going back to my post
>
> For those of you following along at home, here's Jeff's list (I had to
> go and look it up).


Jeff?


> >  1. A library build of Python
> >  2. Templates to stub out a working Python project
> >  3. Libraries to do bridge between native language environments and
> Python
> >  (for me, that's Rubicon)
> >  4. Libraries for utilising native system services (for me, that's Toga)
>
> > - I agree with Kivy on layer 1, and I was able to use
> > their build tools to bootstrap my own. However, I have very different
> > opinions on layers 2-4.
>
> Just to outline the Kivy approach to 2-4: Kivy doesn't really do 2 -- it
> provides examples, and you're supposed to extrapolate from them.  I
> guess that's a form of template.  For #3, there's Kivy's "pyjnius" (to
> access Java via JNI) (https://github.com/kivy/pyobjus) and "pyobjus" (to
> access Objective-C via runtime reflection)
> (https://github.com/kivy/pyjnius).  For #4, as I said, there's "plyer"
> (https://github.com/kivy/plyer).


I'd also include most of Kivy in #4 as well, because that's how they're
tackling the widget issue.

We can have a separate discussion sometime about Django vs. Tornado :-).
>

So - a monkey knife-fight at dawn, then :-)

Yours,
Russ Magee %-)
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