API Notes: InstallerPlugins framework
An introduction to PyObjC describes the general method for translating Objective-C calls into Python calls, including the handling of pass-by-reference arguments and buffers.
This document describes where the PyObjC bindings for this framework are different from the general rule, such as mentioning APIs that are not supported or where the interface is different than expected.
All API’s in the InstallerPlugins framework are wrapped by PyObjC.
I cannot find documentation for this framework on Apple’s developer website anymore, this likely means that this framework is on the way out (even if it doesn’t appear to be officially deprecated).