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

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

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`` makes a simple contract with you:

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

The power of the ``Dependency Injector`` is in its simplicity and straightforwardness. It is a simple tool for the powerful concept.

Example
=======

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.*

Example application container:

.. code-block:: python

   import logging
   import sys

   from dependency_injector import containers, providers

   from . import http, monitors, dispatcher


   class ApplicationContainer(containers.DeclarativeContainer):

       config = providers.Configuration()

       configure_logging = providers.Callable(
           logging.basicConfig,
           stream=sys.stdout,
           level=config.log.level,
           format=config.log.format,
       )

       http_client = providers.Factory(http.HttpClient)

       example_monitor = providers.Factory(
           monitors.HttpMonitor,
           http_client=http_client,
           options=config.monitors.example,
       )

       httpbin_monitor = providers.Factory(
           monitors.HttpMonitor,
           http_client=http_client,
           options=config.monitors.httpbin,
       )

       dispatcher = providers.Factory(
           dispatcher.Dispatcher,
           monitors=providers.List(
               example_monitor,
               httpbin_monitor,
           ),
       )

Example of running of such application:

.. code-block:: python

   from .containers import ApplicationContainer


   def main() -> None:
       container = ApplicationContainer()

       container.config.from_yaml('config.yml')
       container.configure_logging()

       dispatcher = container.dispatcher()
       dispatcher.run()


   if __name__ == '__main__':
       main()

Tutorials
=========

Tutorial is a good point to start.

Choose one of the following:

- `Flask web application tutorial <http://python-dependency-injector.ets-labs.org/tutorials/flask.html>`_
- `Aiohttp REST API tutorial <http://python-dependency-injector.ets-labs.org/tutorials/aiohttp.html>`_
- `Asyncio monitoring daemon tutorial <http://python-dependency-injector.ets-labs.org/tutorials/asyncio-daemon.html>`_

Installation
============

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

    pip install dependency-injector

Documentation
=============

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

Frequently asked questions
==========================

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?
 - autowiring / autoresolving of the dependencies
 - the annotations and ``@inject``-like decorators

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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