What is a Pythonic way for Dependency Injection?

Question

Introduction

For Java, Dependency Injection works as pure OOP, i.e. you provide an interface to be implemented and in your framework code accept an instance of a c

Answer 1

Dependency injection is a simple technique that Python supports directly. No additional libraries are required. Using type hints can improve clarity and readability.

Framework Code:

class UserStore():
    """
    The base class for accessing a user's information.
    The client must extend this class and implement its methods.
    """
    def get_name(self, token):
        raise NotImplementedError

class WebFramework():
    def __init__(self, user_store: UserStore):
        self.user_store = user_store

    def greet_user(self, token):
        user_name = self.user_store.get_name(token)
        print(f'Good day to you, {user_name}!')

Client Code:

class AlwaysMaryUser(UserStore):
    def get_name(self, token):      
        return 'Mary'

class SQLUserStore(UserStore):
    def __init__(self, db_params):
        self.db_params = db_params

    def get_name(self, token):
        # TODO: Implement the database lookup
        raise NotImplementedError

client = WebFramework(AlwaysMaryUser())
client.greet_user('user_token')

The UserStore class and type hinting are not required for implementing dependency injection. Their primary purpose is to provide guidance to the client developer. If you remove the UserStore class and all references to it, the code still works.