> They denote semantics that Python does not have

There is no consensus that "pass by reference" denotes that, whatever a wikipedia editor says. Normal working programmers do not understand "pass by reference" to mean specifically "pass a reference to the caller's stack" but only the more general concept of "pass a reference to the value of a". If you want to talk specifically about what kind of reference gets passed, you need some new terms for that, and both the new terms you come up with will be subtypes of what most of the world will continue to understand as a general category of "pass by reference". No-one outside of these arguments on HN gets confused about whether you can write a swap function in Python; people understand "pass by reference" to mean something more general and entirely true of Python (and Java and so on). You can tell by how often we see those languages described as "pass by reference".

> but it can't. `f` can't change the object which `a` references:

Yes it can. It can't make a to refer to a different object (as your f tries to), but it can change the object a refers to just fine.