I think this should be relegated to the “implementation details, not guaranteed and unobservable unless you use escape hatches” pile. Unfortunately, the set of

I think this should be relegated to the “implementation details, not guaranteed and unobservable unless you use escape hatches” pile. Unfortunately, the set of escape hatches in Python (id, sys.getrefcount, etc. but also in some cases is) is not particularly clearly defined. That doesn’t mean that knowing an implementation detail can’t be useful, just that I feel the way (1) and (2) for lists differ (“semantics”) is of a different nature from the way (1) and (2) for strings differ (“implementation”) and worth keeping in a different mental drawer.