Re: [Pyobjc-dev] A pathetic plea for understanding (MacOS X)

[Steven D. M. <sd...@mi...>]

On Thu, 26 Apr 2001, Deirdre Saoirse Moen wrote:

> I heard about this project on the Jython list and, frankly, it seems
> a more straightforward way of handling the problem of making
> ProjectBuilder/InterfaceBuilder projects.
>
> The catch: I have a lot of python experience, but not a lot mixing it
> with other languages. Even looking through the archives, it's not
> clear to me what is done and what might need to be done.


The best thing for now is probably to look at and try the HelloWorld
program I posted a while back, and look at the apple docs for the
Cocoa classes used. If there's anything you don't understand about it,
ask and I'll try to explain. ( I probably should do a version of the
same program in objective C for comparison, and maybe annotate the
example a bit more. )

> To put it simply, I want to build Cocoa projects and code them in
> Python. I'm learning ObjC (I learned it a few years ago but not
> enough to get fully over the learning curve) and I don't know Java.

Hehe! ;-)  That's sort of what I was hoping for when I got involved.

The truth is that it's not really much of a shortcut right now --
you have to be able to understand enough objective-c to read and
understand the apple Foundation and AppKit docs.

One the bright side, if you already know C, you can .literally. learn
objective-C in a day. ( Learning the whole class library is another
matter! )  And I've been learning lots about the objc runtime by
hacking on PyObjC. ( If you don't know C, I'm afraid that's not a
very bright side! )


> This means I'll want to subclass Cocoa classes in Python -- how close
> is this project to allowing me to do that? Is there some kind of
> guide for how I'd do it either in Jython OR PyObjC? (Ultimately, I'd
> like to try it both ways -- and I'd be more than happy to put up a
> page detailing what has to be done).

You can't subclass Cocoa classes in Python -- objective C classes
are Python objects but not Python classes.  This is the notorious
class/object barrier in Python, and why you need wrapper classes
around dicts and lists and can't directly subclass them.
 You could do the same thing: write a Python wrapper around an
objective C class and subclass that. I'm not sure how I could write
a universal wrapper for all objective-C classes without adding
more introspection capabilities (which is something that's planned,
but not built in -- it can be done with the Neo class inspector --
I'll have to put up some updated instructions on how to get and use
that from Python  -- you can grab the standalone app at:
<http://www.neodata-inc.com/Eng/Self_Introspector.html> )

I would have to say it's not ready for prime time yet.
I don't think you could write a whole non-toy Cocoa app with
Python at present. I haven't been able to get delegate objects
working properly -- which, in the absence of direct subclassing
is probably a requirement. I think I'm going to have to build
an objc-runtime lib from Darwin sources with debugging info,
because I haven't been able to locate the problem with gdb.

I have high hopes for it eventually -- some Apple folks on
other mainling lists have indicated an interest on their part
in opening up ProjectBuilder/InterfaceBuilder to support other
languages,  but I haven't yet figured out how to reanimate a
IB Nib  file from Python yet.

There's a lot of stuff I haven't explored fully yet: for example,
you can load your own objective-C classes as easily as you can
load the AppKit classes. (I've done this with the NeoData class
inspector) and I can say there's a lot less "impedence difference"
between Python and objective-C than between Python and C -- it
makes mixed language programming much easier. I haven't explored
the notion of doing most of a application framework in objective-C
and scripting/customizing  it from Python, but this would
probably work right now. ( Although getting the delegates working
would make it better. )

I would have to admit that right now, PyObjC is mostly for the
adventurous hacker -- but I would sure like to get a few more
adventurous souls to take a hack at it!


-- Steve Majewski