Injecting Existing Instance Example

In this example you’ll see how to supply an already-initialized instance as injectable.

For whatever reason we have already initialized an instance of Application and assigned it to the app variable so we use the injectable_factory decorator in a lambda which in turn just returns the existing app.

Now our InjectingExistingInstance example class can be injected with our existing Application instance.

See also

The injectable_factory decorator can also be used in regular functions and not just in lambdas. The Factory Example shows how to use it.

injecting_existing_instance_example.py

from examples import Example
from examples.injecting_existing_instance.app import Application
from injectable import autowired, Autowired, load_injection_container


class InjectingExistingInstance(Example):
    @autowired
    def __init__(
        self,
        app: Autowired(Application),
    ):
        self.app = app

    def run(self):
        print(self.app.number)
        # 42


def run_example():
    load_injection_container()
    example = InjectingExistingInstance()
    example.run()


if __name__ == "__main__":
    run_example()

app.py

from injectable import injectable_factory


class Application:
    def __init__(self, number):
        self.number = number


app = Application(42)
...

injectable_factory(Application)(lambda: app)