Isolating and injecting the dependency on varys

[ergoregion]

No description provided.

[warrickball]

At the risk of bikeshedding, I wondered why you've called this iMessageRetrieval? My instinct is for something like BaseMessageRetrieval (or even BaseMessageRetriever), indicating this is a base class (i.e., should be subclassed).

I can't quite decide if you mean for this to be an abstract class or not. The design feels to me like you want it to be an abstract class but then you create instances in the tests. (I need to have a look at how Mock() works.)

[warrickball]

I suspect you instantiate iMessageRetrieval in the tests because the retriever has to be that kind of object to satisfy the type hint, but you could redefine the functions in EmptyMessageRetrieval too (or maybe define a MockMessageRetrieval if we expect more tests that need the mocking).

[ergoregion]

Sorry, this is probably my instinct to try to implement interfaces/protocol classes in python whereas python just uses base classes for everything. (I'm doing a dependency injection talk in a few weeks, discussing the approach), I'll look further into python conventions and get back to you.

[warrickball]

If you want to impose that classes can be instantiated unless some functions are implemented, I think you can use the Abstract Base Class module in the standard library but I've never used it myself. I think what you've done is reasonably "Pythonic".

If this did become an abstract base class, then I think you'd have to use EmptyMessageRetrieval and override its functions the same way you're currently doing it.

[ergoregion]

@warrickball I found Protocols which seem to be the python method, I've changed the name and made it a protocol https://typing.readthedocs.io/en/latest/spec/protocol.html#protocols

[warrickball]

Interesting! This (and the comparison with abstract base classes) sounds like demo content to me. 😉