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https://github.com/ets-labs/python-dependency-injector

Dependency injection framework for Python
https://github.com/ets-labs/python-dependency-injector

aiohttp asyncio dependency-injection dependency-injection-container dependency-injection-framework design-patterns factory flask flask-application flask-restful ioc ioc-container python python-2 python-3 python3 singleton threadlocal

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Dependency injection framework for Python

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

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

It helps implement the dependency injection principle.

Key features of the ``Dependency Injector``:

- **Providers**. Provides ``Factory``, ``Singleton``, ``Callable``, ``Coroutine``, ``Object``,
``List``, ``Dict``, ``Configuration``, ``Resource``, ``Dependency``, and ``Selector`` providers
that help assemble your objects.
See `Providers `_.
- **Overriding**. Can override any provider by another provider on the fly. This helps in testing
and configuring dev/stage environment to replace API clients with stubs etc. See
`Provider overriding `_.
- **Configuration**. Reads configuration from ``yaml``, ``ini``, and ``json`` files, ``pydantic`` settings,
environment variables, and dictionaries.
See `Configuration provider `_.
- **Resources**. Helps with initialization and configuring of logging, event loop, thread
or process pool, etc. Can be used for per-function execution scope in tandem with wiring.
See `Resource provider `_.
- **Containers**. Provides declarative and dynamic containers.
See `Containers `_.
- **Wiring**. Injects dependencies into functions and methods. Helps integrate with
other frameworks: Django, Flask, Aiohttp, Sanic, FastAPI, etc.
See `Wiring `_.
- **Asynchronous**. Supports asynchronous injections.
See `Asynchronous injections `_.
- **Typing**. Provides typing stubs, ``mypy``-friendly.
See `Typing and mypy `_.
- **Performance**. Fast. Written in ``Cython``.
- **Maturity**. Mature and production-ready. Well-tested, documented, and supported.

.. code-block:: python

from dependency_injector import containers, providers
from dependency_injector.wiring import Provide, inject

class Container(containers.DeclarativeContainer):

config = providers.Configuration()

api_client = providers.Singleton(
ApiClient,
api_key=config.api_key,
timeout=config.timeout,
)

service = providers.Factory(
Service,
api_client=api_client,
)

@inject
def main(service: Service = Provide[Container.service]) -> None:
...

if __name__ == "__main__":
container = Container()
container.config.api_key.from_env("API_KEY", required=True)
container.config.timeout.from_env("TIMEOUT", as_=int, default=5)
container.wire(modules=[__name__])

main() # <-- dependency is injected automatically

with container.api_client.override(mock.Mock()):
main() # <-- overridden dependency is injected automatically

When you call the ``main()`` function the ``Service`` dependency is assembled and injected automatically.

When you do testing, you call the ``container.api_client.override()`` method to replace the real API
client with a mock. When you call ``main()``, the mock is injected.

You can override any provider with another provider.

It also helps you in a re-configuring project for different environments: replace an API client
with a stub on the dev or stage.

With the ``Dependency Injector``, object assembling is consolidated in a container. Dependency injections are defined explicitly.
This makes it easier to understand and change how an application works.

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:target: https://github.com/ets-labs/python-dependency-injector

Visit the docs to know more about the
`Dependency injection and inversion of control in Python `_.

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

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

pip install dependency-injector

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

The documentation is available `here `_.

Examples
--------

Choose one of the following:

- `Application example (single container) `_
- `Application example (multiple containers) `_
- `Decoupled packages example (multiple containers) `_
- `Boto3 example `_
- `Django example `_
- `Flask example `_
- `Aiohttp example `_
- `Sanic example `_
- `FastAPI example `_
- `FastAPI + Redis example `_
- `FastAPI + SQLAlchemy example `_

Tutorials
---------

Choose one of the following:

- `Flask web application tutorial `_
- `Aiohttp REST API tutorial `_
- `Asyncio monitoring daemon tutorial `_
- `CLI application tutorial `_

Concept
-------

The framework stands on the `PEP20 (The Zen of Python) `_ principle:

.. code-block:: bash

Explicit is better than implicit

You need to specify how to assemble and where to inject the dependencies explicitly.

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

Frequently asked questions
--------------------------

What is 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 😎

How do I start applying 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 specify where to inject it or get it from the container

What price do I pay and what do I get?
- you need to explicitly specify the dependencies
- it will be extra work in the beginning
- it will payoff as project grows

Have a question?
- Open a `Github Issue `_

Found a bug?
- Open a `Github Issue `_

Want to help?
- |star| Star the ``Dependency Injector`` on the `Github `_
- |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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