Add helper that automatically gets services according to type hints?

[hynek]

As it just came up in #86, I use a pattern similar to this all the time:

class Inner:
    ...

@dataclass
class Wrapper:
    foo: Inner

registry.register_factory(Inner, Inner)
registry.register_factory(Wrapper, lambda svcs_container: Wrapper(svcs_container.get(Inner)))

svcs will always be non-magical by default, but I guess nothing speaks against adding a helper that makes the lambda superfluous by looking at the type hints of the factory and calling svcs_container.(a)get on the required types automatically:

registry.register_factory(Inner, Inner)
registry.register_factory(Wrapper, svcs.inspect_and_get(Wrapper))

Since this would only be a helper, it wouldn't also have the pressure to implement all edge cases because the escape hatch of just writing your own lambda is always there.

[pauleveritt]

FWIW I have a registry project with the kind of injection you describe. It’s critical for a larger effort I have in mind.

I’m investigating re-homing my stuff atop svcs… going through a gap analysis now to see which of my darlings (features) to kill.

[proofit404]

To my understanding we have a couple of corner cases here:

1. Please, please, please, do not call it inspect_and_get
2. We need to have sync and async versions of same function
3. handle keyword arguments defaults

   class Srvc:
       a: DepA
       b: DepB = DepB()

   This would be correct case if registry defines only DepA.
4. Passed class could be without type annotations

One benefit I see for factory builder over registry method is ability to customize factory:

fctr = make_factory(Srvc)

def factory(svcs_container):
    with fctr(svcs_container) as instance:
        yield instance

registry.register(Srvc, factory)

In case our service has it's own life circle an supposed to be used as context manager.

[hynek]

To my understanding we have a couple of corner cases here:

1. Please, please, please, do not call it inspect_and_get
2. We need to have sync and async versions of same function

Could both be avoided by making it a class… say… AutoSvc(Wrapper) and adding special logic into svcs's core if necessary?

4. Passed class could be without type annotations

One benefit I see for factory builder over registry method is ability to customize factory:

fctr = make_factory(Srvc)

def factory(svcs_container):
    with fctr(svcs_container) as instance:
        yield instance

registry.register(Srvc, factory)

In case our service has it's own life circle an supposed to be used as context manager.

I don't quite follow here. It kinda sounds like feature-creep? I'm trying to take advantage of type annotations here and not automate away everything to the point of svcs becoming an opaque blog like most DI frameworks. 😅

[proofit404]

@hynek let me put it this way 🌴 🍸

[proofit404]

@hynek I would like to contribute this feature to the project.

Any thoughts on constraints / design decisions mentioned above?

[hynek]

Cool!! I've been meaning to attack the bigger issues in svcs forever but I keep getting pulled into my Big Two (attrs, structlog) all the time. :(

[proofit404]

I'll be hiking in the mountains for next two weeks. Planning to make some progress on this feature before new year.

[hynek]

looong hike @proofit404! 😇

[proofit404]

I had an overlap with team-building event, and family visit for a new year. Actually, today is my first working day since November.

[pauleveritt]

Funny enough, I loaded this stuff (and my thing) back into my brain yesterday.

[pauleveritt]

@proofit404 If you do wind up working on it, I have code/tests for sniffing that I could look at in helping.

[proofit404]

@hynek Hi, finally get time to work on this feature.

What would be final api design decision?

registry.register_factory(Wrapper, svcs.AutoSvc(Wrapper))

[hynek]

Call it auto and the class that presumably gets instantiated AutoService then?

[proofit404]

Why not. If I understand correctly, AutoService would be an internal thing?

[hynek]

Yeah mostly. We’ve got precedents with ServicePing and RegisteredService that allow for limited introspection. Make it definitely frozen, tho.

[hynek]

@proofit404 no rush, but I've noticed that I've been carrying around a bunch of bug fixes that never got released. do you think it makes sense to wait for you? there'll definitely be more releases this year.

[proofit404]

I definitely don't want to be blocker here. Please, release fixes you have.

[proofit404]

Status update: finally got a chance to encorporate svcs into project at work. Hope it will land well, so I wold have a code base to test feature.

[pauleveritt]

@proofit404 If you're still working on the injector code for signature sniffing...I have some code. It's only mediocre, but maybe the test cases are helpful.

[pauleveritt]

@hynek Claude (with some heavy rules and steering) and I have an implementation. Some notes:

• This project targets 3.14 but it's straightforward to target 3.12
• I kept that file as free of scope-creep as I could
• It has a companion auto.pyi for reasons that are explained in the package
• It has one architecture astronauting
  • It gets the injector from the registry
  • This allows alternate injectors
  • I have two in this package
  • Spot your name in the README and you'll find more details in the note I left you