simple-di

from simple_di import Container, Provider class MyConfig(Container): debug_mode = Provider(bool, default=False) database_url = Provider(str, default="sqlite:///test.db") class MyDependencies(Container): # Instantiate nested containers config = MyConfig() # A factory function for a database client def _create_db_client(url: str): print(f"[DB] Connecting to {url}...") return f"DatabaseClient({url})" # Define a provider for the database client, depending on config.database_url db_client = Provider(_create_db_client, config.database_url) # A factory function for the main application def _create_app(client): print(f"[App] Creating app with client: {client}") return f"MyApp({client})" # Define a provider for the app, depending on db_client app = Provider(_create_app, db_client) # Instantiate the main dependency container my_app_deps = MyDependencies() # Accessing dependencies (calling .get() is crucial to resolve them) print("\n--- First Resolution ---") db_client_instance = my_app_deps.db_client.get() print(f"Retrieved DB Client: {db_client_instance}") app_instance = my_app_deps.app.get() print(f"Retrieved App: {app_instance}") # Overriding a configuration value and observing changes print("\n--- Overriding Configuration ---") my_app_deps.config.database_url.set("postgresql://user:pass@host/prod_db") # Accessing again will re-evaluate the db_client provider due to dependency change print("\n--- Second Resolution (after override) ---") new_db_client_instance = my_app_deps.db_client.get() print(f"Retrieved NEW DB Client: {new_db_client_instance}") # Accessing app again will use the new db client new_app_instance = my_app_deps.app.get() print(f"Retrieved NEW App: {new_app_instance}")