ets-labs / python-dependency-injector

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.

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

Example application container:

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:

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
• Aiohttp REST API tutorial
• Asyncio monitoring daemon tutorial
• CLI application tutorial

Installation

• The package is available on the PyPi:

  pip install dependency-injector
  

Documentation

• The documentation is available on the Read The Docs

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

Found a bug?

• Open a Github Issue

Want to help?

• ⭐️ Star the Dependency Injector on the Github
• 🆕 Start a new project with the Dependency Injector
• 💬 Tell your friend about the Dependency Injector

Want to contribute?

• 🔀 Fork the project
• ⬅️ Open a pull request to the develop branch