Frequently Asked Questions

If I use inject() or scope decorators on my classess will I be able to create instances of them without using Injector?

Yes. Scope decorators don’t change the way you can construct your class instances without Injector interaction.

I’m calling this method (/function/class) but I’m getting “TypeError: XXX() takes exactly X arguments (Y given)”

Example code:

class X:
    @inject
    def __init__(self, s: str):
        self.s = s

def configure(binder):
    binder.bind(s, to='some string')

injector = Injector(configure)
x = X()

Result?

TypeError: __init__() takes exactly 2 arguments (1 given)

Reason? There’s no global state that Injector modifies when it’s instantiated and configured. Its whole knowledge about bindings etc. is stored in itself. Moreover inject() will not make dependencies appear out of thin air when you for example attempt to create an instance of a class manually (without Injector‘s help) - there’s no global state @inject decorated methods can access.

In order for X to be able to use bindings defined in @inject decoration Injector needs to be used (directly or indirectly) to create an instance of X. This means most of the time you want to just inject X where you need it, you can also use Injector.get() to obtain an instance of the class (see its documentation for usage notes).