Dependency Injector
===================

*Dependency Injector* is a Python dependency injection framework. It was 
designed to be unified, developer's friendly tool for managing any kind
of Python objects and their dependencies in formal, pretty way.

Below is a list of some key features and points of *Dependency Injector*:

- Easy, smart, pythonic style.
- Obvious, clear structure.
- Memory efficiency.
- Thread safety.
- Semantic versioning.

Main idea of *Dependency Injector* is to keep dependencies under control.

Status
------

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Installation
------------

*Dependency Injector* library is available on PyPi_::

    pip install dependency_injector

Documentation
-------------

*Dependency Injector* documentation is hosted on ReadTheDocs:

- `User's guide`_ 
- `API docs`_

Examples
--------

.. code-block:: python

    """Pythonic way for Dependency Injection."""

    from dependency_injector import providers
    from dependency_injector import injections


    @providers.DelegatedCallable
    def get_user_info(user_id):
        """Return user info."""
        raise NotImplementedError()


    @providers.Factory
    @injections.inject(get_user_info=get_user_info)
    class AuthComponent(object):
        """Some authentication component."""

        def __init__(self, get_user_info):
            """Initializer."""
            self.get_user_info = get_user_info

        def authenticate_user(self, token):
            """Authenticate user by token."""
            user_info = self.get_user_info(user_id=token + '1')
            return user_info


    print AuthComponent
    print get_user_info


    @providers.override(get_user_info)
    @providers.DelegatedCallable
    def get_user_info(user_id):
        """Return user info."""
        return {'user_id': user_id}


    print AuthComponent().authenticate_user(token='abc')
    # {'user_id': 'abc1'}

Example of catalog usage:

.. code-block:: python

    """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."""

        @providers.Singleton
        def database():
            """Provide database connection.

            :rtype: providers.Provider -> sqlite3.Connection
            """
            return sqlite3.connect(':memory:')

        @providers.Factory
        @injections.inject(db=database)
        def users(**kwargs):
            """Provide users service.

            :rtype: providers.Provider -> UsersService
            """
            return UsersService(**kwargs)

        @providers.Factory
        @injections.inject(db=database)
        @injections.inject(users_service=users)
        def auth(**kwargs):
            """Provide users service.

            :rtype: providers.Provider -> AuthService
            """
            return AuthService(**kwargs)


    # 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()


    # Overriding auth service provider and making some asserts:
    class ExtendedAuthService(AuthService):
        """Extended version of auth service."""

        def __init__(self, db, users_service, ttl):
            """Initializer."""
            self.ttl = ttl
            super(ExtendedAuthService, self).__init__(db=db,
                                                      users_service=users_service)


    class OverriddenServices(Services):
        """Catalog of service providers."""

        @providers.override(Services.auth)
        @providers.Factory
        @injections.inject(db=Services.database)
        @injections.inject(users_service=Services.users)
        @injections.inject(ttl=3600)
        def auth(**kwargs):
            """Provide users service.

            :rtype: providers.Provider -> AuthService
            """
            return ExtendedAuthService(**kwargs)


    auth_service = Services.auth()

    assert isinstance(auth_service, ExtendedAuthService)

One more example with catalog:

.. code-block:: python

    """Pythonic way for Dependency Injection (example with Catalog)."""

    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, ':memory:')
        """:type: providers.Provider -> sqlite3.Connection"""

        users = providers.Factory(UsersService,
                                  db=database)
        """:type: providers.Provider -> UsersService"""

        auth = providers.Factory(AuthService,
                                 db=database,
                                 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()


    # Overriding auth service provider and making some asserts:
    class ExtendedAuthService(AuthService):
        """Extended version of auth service."""

        def __init__(self, db, users_service, ttl):
            """Initializer."""
            self.ttl = ttl
            super(ExtendedAuthService, self).__init__(db=db,
                                                      users_service=users_service)


    Services.auth.override(providers.Factory(ExtendedAuthService,
                                             db=Services.database,
                                             users_service=Services.users,
                                             ttl=3600))


    auth_service = Services.auth()

    assert isinstance(auth_service, ExtendedAuthService)

You can get more *Dependency Injector* examples in ``/examples`` directory on
GitHub:

    https://github.com/ets-labs/dependency_injector


Feedback
--------

Feel free to post questions, bugs, feature requests, proposals etc. on
*Dependency Injector*  GitHub Issues:

    https://github.com/ets-labs/dependency_injector/issues

Your feedback is quite important!


.. _PyPi: https://pypi.python.org/pypi/dependency_injector
.. _User's guide: http://dependency_injector.readthedocs.org/en/stable/
.. _API docs: http://dependency-injector.readthedocs.org/en/stable/api/
.. _SLOC: http://en.wikipedia.org/wiki/Source_lines_of_code
.. _SOLID: http://en.wikipedia.org/wiki/SOLID_%28object-oriented_design%29
.. _IoC: http://en.wikipedia.org/wiki/Inversion_of_control
.. _dependency injection: http://en.wikipedia.org/wiki/Dependency_injection