injector_command_bus.py

# tested on Python3.9 with just injector installed (pip install injector==0.18.4)
from dataclasses import dataclass
from typing import TypeVar, Generic

from injector import Injector, Module, provider


TCommand = TypeVar("TCommand")


class Handler(Generic[TCommand]):
    def __call__(self, command: TCommand) -> None:
        raise NotImplementedError



@dataclass(frozen=True)
class Enrol:
    student_id: int
    course_id: int



class EnrolHandler(Handler[Enrol]):
    def __call__(self, command: Enrol) -> None:
        print(f"command: {command}")



class Enrolment(Module):
    @provider
    def enrol_handler(self) -> Handler[Enrol]:
        return EnrolHandler()


class CommandBus:
    def __init__(self, container: Injector) -> None:
        self._container = container

    def handle(self, command: TCommand) -> None:
        command_cls: Type[TCommand] = type(command)
        handler = self._container.get(Handler[command_cls])
        handler(command)


container = Injector([Enrolment()], auto_bind=False)
command_bus = CommandBus(container)
command_bus.handle(Enrol(student_id=123000, course_id=666))