[Pyobjc-dev] Proper way to expose custom Obj-C classes to Python?

[Ian M. <ip...@po...>]

Hi,

I'm trying to determine the best way to expose custom,
application-specific, non-system-framework (i.e. not in one of the
framework wrappers provided with PyObjC) classes written in Objective-C to
python across the PyObjC bridge. My eventual hope is to develop a "hybrid"
application in which some portions of the app are in Objective-C and others
are in python, with the two side integrating via the PyObjC bridge. Most of
the documentation I've been able to find seems to focus on situations where
the goal is to have all the app-specific code be in python, and to have the
python call out to AppKit classes, etc via the bridge and the pre-packaged
system framework wrappers.

I've not seen any indication that it's possible to expose classes from an
app. But I did find this web page:
https://pythonhosted.org/pyobjc/dev/wrapping.html which makes it sound like
the best way would be for me to move any classes that need to be visible to
python out of my application, and into a framework (which I can embed in my
application), and then to adapt an existing framework wrapper to wrap this
newly-created framework. So far, the wrapper-adapting part is proving to be
easier said that done.

Looking at the existing wrappers, many of them have a compiled component
(i.e. .m files). As far as I can tell, that seems to be responsible for
bringing in protocols, constants and C functions. That said, it's not clear
to me what all triggers the need for a compiled extension. I also saw that
the _metadata.py files in existing wrappers have this at the top of them:
"This file is generated by objective.metadata". I tracked that down to this
repo: https://bitbucket.org/ronaldoussoren/objective.metadata which, with
some coaxing I could get to build, install and run, but I've not gotten it
to do anything useful yet -- i.e. how I get it to generate these
_metadata.py files is not obvious.

I'm content to keep fighting through the source on my own, but there's this
part of my mind saying, "You've *got* to be missing something. It can't
possibly be this involved to expose a framework to python." I can
understand the overhead for exposing C functions and constants, but all the
Objective-C stuff should be doable at runtime, right?

So, in sum:

1) Is this the right way to expose Objective-C classes to Python?

Assuming yes...

2) Exhaustively speaking, what triggers the need for a compiled extension?
3) What is the magic invocation to get objective.metadata to spit out the
_metadata.py files for my framework?
4) Any other tips that might help in with this "hybrid" app goal?

Many thanks,
Ian