But if you need the start of the full expression, can't you just go up in the "parent" chain until the parent is not an expression any more?

Could additional API be introduced which provides the value I am looking for as well as the one you need?

I was not on the nosy list by the way, I just put myself there after I commented. And that was after 3.4.3, after I noticed my software was suddenly broken by a patch release of python.