Let's try simpler: No code that runs under the GIL is ever run concurrently. All of the code in the example holds the GIL, there's never any concurrency in you

Let's try simpler: No code that runs under the GIL is ever run concurrently. All of the code in the example holds the GIL, there's never any concurrency in your article! With no concurrency, there can be no data race.