There should be one, and only one, obvious way to do it.
This is a key misunderstanding. You CANNOT "append" to lots of collections.
You can ADD to a set, which has a quite different semantics than appending (and hence a different name). You can neither add nor append to a string because they are immutable.
I can imagine various collections where appending might make sense (mutable strings?). None of them are in builtins. If a 3rd party wrote such a collection with append semantics, they'd probably name it append... e.g. collections.deque has an "append" (but also an "appendleft").