> I think it's a common practice to create constants for such hardcoded
> values.

Yep, _FINAL_MARKER is clearer here that a cryptic character.  An alternate fix would be to use a c as rc marker (like what Python itself does in sys.hexversion and elsewhere).

I’ll see if I can use only one object instead of two.

> Anyway, I can't find packaging package in default branch of python.
The merge started at the PyCon sprints is still underway at https://bitbucket.org/tarek/cpython/  Follow the fellowship ML for details.  There’ll be an announcement on python-dev too when it’s complete, and then we’ll restart fixing bugs.