> Trying to open a file that doesn't exist isn't by itself an exceptional incident. The calling code might consider it an exception and decide to raise, but the IO library shouldn't.

This is a way of thinking that I don't get. Yes it's fine that an IOLibrary has to be able to handle a FileDoesNotExistError condition. But from the caller POV: I clearly instructed you to open a file of some description. I expect you to return to me a handle for said file. Everything that does not match that expectation is exceptional (to the caller).

And it is that violation of expectations that is communicated by (Python's) exceptions.