Re: Using ctypes to access OS X frameworks

On Oct 15, 2004, at 1:20 PM, Thomas Heller wrote:

> I have been asked in private email if ctypes can be used to access OS X
> frameworks.  I googled around a bit and found these pages:
>
> http://developer.apple.com/samplecode/CallMachOFramework/ 
> CallMachOFramework.html
>
> http://developer.apple.com/samplecode/CallMachOFramework/listing2.html
>
> Remember that I know nearly nothing about macs, but by reading these
> pages I got the impression that the key functions here are
> LoadFrameworkBundle() and CFBundleGetFunctionPointerForName(), which
> seem to play roles similar to dl_open()/dl_sym() or
> LoadLibrary()/GetProcAddress().

All of the function lookup code in OS X nomatter which API it's from  
boils down to dyld.  libdl is implemented as a shim over top of dyld,  
so ctypes can already be used to load code from frameworks.  All you  
have to do is point it at the code in the bundle, which is always  
Foo.framework/Versions/Current/Foo .. as opposed to libfoo.so on other  
platforms.

> Apart from that, I really do not know if this is a niche covered by
> PyObjC, or would ctypes have a place here?

PyObjC in SVN does wrap CFBundleGetFunctionPointer for name  
(objc.loadBundleFunctions, IIRC) and can do some, not all, of the  
things that ctypes does.  It's primarily useful if you're calling into  
functions that are CoreFoundation based, or deal with very basic types  
(integers, floats, simple structures, etc.).

Here is an example that uses PyObjC to do something ctypes-like.  Note  
that it's a lot less ugly if the functions are shoved into globals..  
but I wanted to make sure all of the functions exist at runtime because  
CPS is undocumented private SPI and may disappear in the future.

http://svn.red-bean.com/pyobjc/trunk/pyobjc/Examples/wmEnable.py

I've been meaning to experiment with ctypes more on OS X, but I have  
simply been too busy :(

-bob


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