new_contents: """Concept example of `Dependency Injector`."""
  
  import sqlite3
  
  from dependency_injector import catalogs
  from dependency_injector import providers
  from dependency_injector import injections
  
  
  class UsersService(object):
      """Users service, that has dependency on database."""
  
      def __init__(self, db):
          """Initializer."""
          self.db = db
  
  
  class AuthService(object):
      """Auth service, that has dependencies on users service and database."""
  
      def __init__(self, db, users_service):
          """Initializer."""
          self.db = db
          self.users_service = users_service
  
  
  class Services(catalogs.DeclarativeCatalog):
      """Catalog of service providers."""
  
      database = providers.Singleton(sqlite3.connect,
                                     injections.Arg(':memory:'))
      """:type: providers.Provider -> sqlite3.Connection"""
  
      users = providers.Factory(UsersService,
                                injections.KwArg('db', database))
      """:type: providers.Provider -> UsersService"""
  
      auth = providers.Factory(AuthService,
                               injections.KwArg('db', database),
                               injections.KwArg('users_service', users))
      """:type: providers.Provider -> AuthService"""
  
  
  # Retrieving catalog providers:
  users_service = Services.users()
  auth_service = Services.auth()
  
  # Making some asserts:
  assert users_service.db is auth_service.db is Services.database()
  assert isinstance(auth_service.users_service, UsersService)
  assert users_service is not Services.users()
  assert auth_service is not Services.auth()
  
  
  # Making some "inline" injections:
  @injections.inject(users_service=Services.users)
  @injections.inject(auth_service=Services.auth)
  @injections.inject(database=Services.database)
  def example(users_service, auth_service, database):
      """Example callback."""
      assert users_service.db is auth_service.db
      assert auth_service.db is database
      assert database is Services.database()
  
  
  # Making a call of decorated callback:
  example()
  
subject: Add new one concept example that uses full syntax