python-dependency-injector/examples/providers/dependency.py

"""`Dependency` provider example."""

import abc
import dataclasses

from dependency_injector import containers, providers, errors


class DbAdapter(metaclass=abc.ABCMeta):
    ...


class SqliteDbAdapter(DbAdapter):
    ...


class PostgresDbAdapter(DbAdapter):
    ...


@dataclasses.dataclass
class UserService:
    database: DbAdapter


class Container(containers.DeclarativeContainer):

    database = providers.Dependency(instance_of=DbAdapter)

    user_service = providers.Factory(
        UserService,
        database=database,
    )


if __name__ == '__main__':
    container1 = Container(database=providers.Singleton(SqliteDbAdapter))
    container2 = Container(database=providers.Singleton(PostgresDbAdapter))

    assert isinstance(container1.user_service().database, SqliteDbAdapter)
    assert isinstance(container2.user_service().database, PostgresDbAdapter)

    container3 = Container(database=providers.Singleton(object))
    try:
        container3.user_service()
    except errors.Error as exception:
        print(exception)
        # The output is:
        # <object object at 0x107ce5c40> is not an
        # instance of <class '__main__.DbAdapter'>