python-dependency-injector/README.rst

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What is ``Dependency Injector``?
================================

``Dependency Injector`` is a dependency injection framework for Python.

The power of the framework is in its simplicity and straightforwardness.

It stands on two principles:

- Explicit is better than implicit (PEP20).
- Do no magic to your code.

How does it different from the other frameworks?

- **No autowiring.** The framework does NOT do any autowiring / autoresolving of the dependencies. You need to specify everything explicitly. Because *"Explicit is better than implicit" (PEP20)*.
- **Does not pollute your code** .Your application does NOT know and does NOT depend on the framework. No ``@inject`` decorators, annotations, patching or any other magic tricks.

``Dependency Injector`` follows a simple contract with you:

- You tell the framework how to build you code
- The framework does it for you

``Dependency Injector`` is a simple tool for the powerful concept.

People often ask
----------------

Here is a short summary of what is often asked about the dependency injection and the Dependency Injector.

What is the dependency injection?
 ⁃ dependency injection is a principle that decreases coupling and increases cohesion

Why should I do the dependency injection?
 ⁃ your code becomes more flexible, testable and clear
 ⁃ you have no problems when you need to understand how it works or change it 😎 

How do I start doing the dependency injection?
 ⁃ you start writing the code following the dependency injection principle
 ⁃ you register all of your application components and their dependencies in the container
 ⁃ when you need a component, you get it from the container

Why do I need a framework for this?
 ⁃ you need the framework for this to not create it by your own
 ⁃ this framework gives you the container and the providers
 ⁃ the container is like a dictionary with the batteries 🔋 
 ⁃ the providers manage the lifetime of your components, you will need factories, singletons, smart config object etc

What price do I pay and what do I get?
 ⁃ you need to explicitly specify the dependencies in the container
 ⁃ it will be extra work in the beginning
 ⁃ it will payoff when project grows or in two weeks 😊 (when you forget what project was about)

What features does the framework have?
 ⁃ building objects graph
 ⁃ smart configuration object
 ⁃ providers: factory, singleton, thread locals registers, etc
 ⁃ positional and keyword context injections
 ⁃ overriding of the objects in any part of the graph

What features the framework does NOT have?
 ⁃ auto wiring / auto resolving of the dependencies
 ⁃ the annotations and ``@inject``-like decorators

Why do I need it?
=================

``Dependency Injector`` helps you understand and change the structure of the application.

With the ``Dependency Injector`` you keep **application structure in one place**.
This place is called **the container**. You use the container to manage all the components of the
application. All the component dependencies are defined explicitly. This provides the control on
the application structure. It is **easy to understand and change** it.

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*The container is like a map of your application. You always know what depends on what.*

``Flask`` + ``Dependency Injector`` example application container:

.. code-block:: python

    from dependency_injector import containers, providers
    from dependency_injector.ext import flask
    from flask import Flask
    from flask_bootstrap import Bootstrap
    from github import Github

    from . import views, services


    class ApplicationContainer(containers.DeclarativeContainer):
        """Application container."""

        app = flask.Application(Flask, __name__)

        bootstrap = flask.Extension(Bootstrap)

        config = providers.Configuration()

        github_client = providers.Factory(
            Github,
            login_or_token=config.github.auth_token,
            timeout=config.github.request_timeout,
        )

        search_service = providers.Factory(
            services.SearchService,
            github_client=github_client,
        )

        index_view = flask.View(
            views.index,
            search_service=search_service,
            default_query=config.search.default_query,
            default_limit=config.search.default_limit,
        )

Running such container looks like this:

.. code-block:: python

    from .containers import ApplicationContainer


    def create_app():
        """Create and return Flask application."""
        container = ApplicationContainer()
        container.config.from_yaml('config.yml')
        container.config.github.auth_token.from_env('GITHUB_TOKEN')

        app = container.app()
        app.container = container

        bootstrap = container.bootstrap()
        bootstrap.init_app(app)

        app.add_url_rule('/', view_func=container.index_view.as_view())

        return app

And testing looks like:

.. code-block:: python

    from unittest import mock

    import pytest
    from github import Github
    from flask import url_for

    from .application import create_app


    @pytest.fixture
    def app():
        return create_app()


    def test_index(client, app):
        github_client_mock = mock.Mock(spec=Github)
        # Configure mock

        with app.container.github_client.override(github_client_mock):
            response = client.get(url_for('index'))

        assert response.status_code == 200
        # Do more asserts

See complete example here - `Flask + Dependency Injector Example <https://github.com/ets-labs/python-dependency-injector/tree/master/examples/miniapps/ghnav-flask>`_

How to install?
---------------

- The package is available on the `PyPi`_::

    pip install dependency-injector

Where is the docs?
------------------

- The documentation is available on the `Read The Docs <http://python-dependency-injector.ets-labs.org/>`_

Have a question?
----------------

- Open a `Github Issue <https://github.com/ets-labs/python-dependency-injector/issues>`_

Found a bug?
------------

- Open a `Github Issue <https://github.com/ets-labs/python-dependency-injector/issues>`_

Want to help?
-------------

- |star| Star the ``Dependency Injector`` on the `Github <https://github.com/ets-labs/python-dependency-injector/>`_
- |new| Start a new project with the ``Dependency Injector``
- |tell| Tell your friend about the ``Dependency Injector``

Want to contribute?
-------------------

- |fork| Fork the project
- |pull| Open a pull request to the ``develop`` branch

.. _PyPi: https://pypi.org/project/dependency-injector/

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