The build script for a Mac OS installer, in
Mac/BuildScript/build-installer.py, currently requires OS 10.4 and
Python 2.3.  At some point it will have to be ported to a newer version
of Python (and Mac OS).  It uses a number of modules which are slated
for future removal, particularly Carbon and MacOS.  These modules are
only used in the function "setIcon".  They can be replaced with a call
to a Cocoa method via PyObjC.  The "setIcon" function using PyObjC would
look like this:

def setIcon(folder, imagefile):

    try:

        import os, AppKit

        AppKit.NSApplicationLoad()      # initialize Cocoa

        return
AppKit.NSWorkspace.sharedWorkspace().setIcon_forFile_options_(
            AppKit.NSImage.alloc().initWithContentsOfFile_(imagefile),
            os.path.abspath(folder), 0)

    except ImportError:
        return False

Usage of PyObjC in the build-script should be avoided, as should eating 
exceptions like you propose. The rationale for not silencing exceptions is 
that the build script is supposed to enable reproducable builds.

I'll probably add a small Cocoa ObjC program to the BuildScript directory 
that uses the API's you mention.

The attached patch shows what I intent do commit after testing. This adds 
a small ObjC command-line tool that sets the icon.  I still have to build 
the installer to check if the patch actually works.

Looks good.  The contrast is stark.

Fixed in r70727 (trunk), r70728 (2.6) and r70729 (3.1)