When working on the original reference implementation for PEP 432, I found it useful to split the startup & shutdown code out from the main entry points into the eval loop (see issue 22257 for more details).

However, that split made the draft implementation rather hard to maintain - any CPython commit that touched pythonrun.c was almost certain to cause a merge conflict.

The attached patch is a preliminary split into two separate modules, with pythonrun continuing to hold the main eval loop entry points, while the startup and shutdown code moves into pylifecycle.

This is an initial WIP patch (that nonetheless passes the test suite). I started work on it a few months ago, so I need to make sure that I've retained Victor's recent pythonrun changes.