DI (Dependency Injection) in Python

DI with Python

There seems to be no demand, but I happened to find out how to DI with Python, so ...

Several options

• Injector (Documents are here)
• Inject (There was Japanese article) -siringa (Documents are here)
• di-py

Inject seems to have stopped developing in 2015. di-py doesn't seem to be very well documented. I avoided siringa because it was a bit of a metamorphic way to inject type hints.

I tried Injector by elimination method.

Injector features

As explained in the documentation, it's a Google Guice -like framework. The explanation of Google Guice was easy to understand in this article. Google Guice usage memo

Terms such as Inject, Module, and Provider are almost the same as Google Guice, so it may be easier to understand Guice first. (Although there are still type hints, doing DI in a scripting language was hard to understand)

Implementation example

DI the instance

todo_usecase.py

@singleton
class TodoUseCase:

    def register(self, todo: Todo) - > None:
        print("call todo_usecase.register")

todo_controller.py

@singleton
class TodoController:

    @inject
    def __init__(self, todo_usecase: TodoUseCase) -> None:
        self.todo_usecase = todo_usecase

    def create_todo(self, todo: Todo) -> None:
        self.todo_usecase.register(todo)

if __name__=='__main__':
    injector = Injector()
    todo_controller: TodoController = injector.get(TodoController)

    todo: Todo = Todo()

    todo_controller.create_todo(todo)

If you want to DI a normal instance, just @Inject will do the DI for you. By default, it seems to be a singleton by giving @singleton instead of a singleton. (Guice is also not a singleton by default)

DI an instance of the implementation class

todo_repository.py

class TodoRepository:

    @abstractmethod
    def register(self, todo: Todo) -> None:
        raise NotImplementedError

todo_datasource.py

class TodoDataSource(TodoRepository):

    def register(self, todo: Todo) -> None:
        print("call todo_datasource.register")

todo_usecase.py

@singleton
class TodoUseCase:

　　　　　　　　@inject
    def __init__(self, todo_repository: TodoRepository) -> None:
        self.todo_repository = todo_repository

    def register(self, todo: Todo) -> None:
        self.todo_repository.register(todo=todo)

class TodoDIModule(Module):
    def configure(self, binder):
        binder.bind(TodoRepository, to=TodoDataSource, scope=singleton)

if __name__=='__main__':
    injector = Injector([TodoDIModule()])
    todo_use_case: TodoUseCase = injector.get(TodoUseCase)

    todo: Todo = Todo()

    todo_use_case.register(todo)

The point is to set DI in the implementation class of Module. It seems that the method of making it a singleton can also be done by specifying the scope in Module.

that's all.