When running the following command from the Doc/ directory:

    ./venv/bin/sphinx-build -Q -b gettext -D gettext_compact=0 . ../pot/

everything goes right, but when running the following from cpython direcory:

    ./Doc/venv/bin/sphinx-build -Q -b gettext -D gettext_compact=0 Doc pot

we get:

    Extension error:
    Could not import extension asdl_highlight (exception: No module named 'asdl')

This is because sys.path.append(os.path.abspath("../Parser/")) starts from the current directory, cpython/../Parser don't exists while Doc/../Parser exists.

It could be fixed by starting with a Path(__file__).resolve(), will PR it.