How does Dependency Injection help manage dependencies in an application?

Dependency Injection (DI) helps manage dependencies in an application by allowing necessary objects (dependencies) to be passed into a class from outside, rather than creating them inside the class. This increases modularity, simplifies testing, and makes component replacement easier.

For example, instead of the class creating a database object itself, it receives it through a constructor or setter:

class Database:
    def query(self):
        return "data"

class Service:
    def __init__(self, db: Database):
        self.db = db

    def get_data(self):
        return self.db.query()

# Dependency injection
db_instance = Database()
service = Service(db_instance)

This approach makes it easy to replace Database with a mock object during testing or to use a different implementation without changing the Service class.