[Pythonmac-SIG] Grokking bgen and the toolbox modules

[Donovan Preston]

Hi,

I'm trying to figure out how best to program some functionality which 
will heavily rely on the Mac OS Toolbox. I'd like to do some things with 
creating a QuickTime movie, adding tracks to it, etc, as well as 
managing controls created by Carbon from a Carbon Nib file.

First off, I was looking at the sample code provided by Apple on OS X in 
/Developer/Examples/Carbon/AppearanceSample. It  looks like they are 
using two toolbox calls to get a reference to a control by ID and then 
get it's data. It looks like this:

GetControlByID( GetWindowRef(), &kChoosePopup, &fChoosePopup );
GetControlData( fChoosePopup, 0, kControlPopupButtonMenuRefTag, sizeof
( menu ), &menu, &actual );

How would I go about converting this to Python code that calls bgen 
generated functions? I note that there is a module named Ctl, and also 
that there is a function GetControlByID in there. So far so good. I note 
by looking at Apple's developer documentation that the parameter types 
are WindowRef, ControlID, and ControlRef (is there a better way to find 
out parameter types, like a docstring on a method? Is there a way to 
find this out interactively in python?)

How do I generate a window reference which I can pass to this function, 
as well as a ControlID record? I know from looking at some other bgen 
code that the final parameter is actually being returned to me and 
python will return a nice object with the Control.

I also can guess from looking at some other bgen generated code that 
GetControlData will be a method of the Control object which is returned. 
I am assuming that because I don't see GetControlData in dir(Ctl) and 
GetControlData takes a ControlRef as the first parameter. Am I wrong?

I guess what I am asking, is how exactly is bgen generated code 
produced? How does it know to be so smart as to turn some things into 
return values and some returned data into objects? And how does one go 
about using bgen generated code from Python, as far as having any sort 
of reference or documentation, besides reading the code? (Which isn't 
too hard, really...)

Also, Jack, you mentioned in passing a while back that you would like 
for some of the CarbonNib functions I had written to be generated 
automatically by bgen. How exactly would one go about doing that, and 
how would someone know what functions have and have not been done?

Finally, when I was trying to create a QuickTime movie earlier, some of 
the parameters needed to be set to NULL, but Python wouldn't allow me to 
pass None. Here's the code:

(resRefNum, myMovie) = Qt.CreateMovieFile(fsspec, "TVOD", 
smSystemScript, 0)
myTrack = myMovie.NewMovieTrack(170 << 16, 85 << 16, Sound.kNoVolume);
kSpriteMediaTimeScale = 600
myMedia = myTrack.NewTrackMedia("SPRT", kSpriteMediaTimeScale, None, 
None);

I need to pass None as the final two parameters, but Python won't let 
me. I fixed the NewTrackMedia function by setting the third parameter 
conversion function (right terminology?) from ResObj_Convert, which 
won't accept Python's None, to OptResObj_Convert, which accepts Python's 
None object and returns NULL to the C code. However, the fourth 
parameter, which uses the conversion function PyMac_GetOSType, doesn't 
allow me to pass None, and I can't seem to find one that does.

I gave up on trying to get the above code to work. Is it even possible?

I'd like to help out maintaining these toolbox modules so I can use them 
in my code, but I need help understanding them first.

Sorry for asking so many questions, but I feel like there's so much 
power there that I just can't use because I don't quite understand it!

Donovan