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Dependency injection microframework for Python

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What is Dependency Injector?

Dependency Injector is a dependency injection framework for Python.

It helps you implement the dependency injection principle.

What is dependency injection?

Dependency injection is a principle that helps to decrease coupling and increase cohesion. Your code becomes more flexible, clear and it is easier to test it.

How to implement dependency injection?

Objects do not create each other anymore. They provide a way to inject the needed dependency instead.

Before:

class ApiClient:

    def __init__(self):
        self.api_key = os.getenv('API_KEY')
        self.timeout = os.getenv('TIMEOUT')


class Service:

    def __init__(self):
        self.api_client = ApiClient()

After:

class ApiClient:

    def __init__(self, api_key: str, timeout: int):
        self.api_key = api_key
        self.timeout = timeout


class Service:

    def __init__(self, api_client: ApiClient):
        self.api_client = api_client

Who creates the objects now? Look at the next section.

What does Dependency Injector do?

Dependency Injector provides you with the container and the providers that help you build your application objects when you apply dependency injection principle:

from dependency_injector import containers, providers


class ApiClient:

    def __init__(self, api_key: str, timeout: int):
        self.api_key = api_key
        self.timeout = timeout


class Service:

    def __init__(self, api_client: ApiClient):
        self.api_client = api_client


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,
    )


if __name__ == '__main__':
    container = Container()
    container.config.from_yaml('config.yml')

    service = container.service()

    assert isinstance(service.api_client, ApiClient)

More examples

Installation

The package is available on the PyPi:

pip install dependency-injector

Documentation

The documentation is available on the Read The Docs

Concept

Dependency Injector 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.

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?
Found a bug?
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

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