There's plenty of reading in the set of links in the grandparent, so maybe I can just quickly clarify. When we speak of concurrency and data races, we're speaki

There's plenty of reading in the set of links in the grandparent, so maybe I can just quickly clarify. When we speak of concurrency and data races, we're speaking about concurrent accesses to a particular memory location, where concurrent means "at the same or overlapping times". In Python at this level, we don't even have a notion of a memory address. In fact, the memory address of where the integer itself is stored is going to be different, since integers in Python are boxed and immutable. Even if that weren't the case and these were direct memory accesses as you'd see in a lower level language, this would still not be able to introduce a data race, as the GIL prevents these two threads from ever actually running at the same time (while executing pure-python code that does not otherwise release the GIL. A poorly written extension or buggy code outside the GIL could cause data races, but that's a bit of a rabbithole). They'll hop back and forth as they acquire/release the GIL, and so the memory accesses can never race.