Write more about purposes of the library: exceptions + data classes ⇒ control flow

[anatoly-scherbakov]

The library documentation refers to a few articles about how exceptions might be used in controlling the control flow of an application. This is an interesting topic to explore further.

I personally very much like to write exceptions as dataclasses and inherit them from DocumentedError. This allows me to encapsulate business logic related information in those exceptions, and then to easily retrieve it in other parts of the application. For instance, I can do something like this:

def ask_hal(question: str, user_name: str):
    try:
        return hal.ask(question)
    except AnswerToAnswer as err:
        raise dataclasses.replace(
            err,
            user_name=user_name,
        )

In this question, we do not provide user_name to the internal layer of the application which is responsible for communication with HAL9000 computer, but we catch the error, enhance it with information available in the API layer, and reraise. Voilà.

Also

ExceptionList, a new feature introduced into Python recently, can be mentioned in relation to this topic.

When?

No idea; perhaps at some point I get inspired by a particular usage example and will get to writing this piece.