simple-dependency-injector

Dependency Injector for Python

A simple and flexible dependency injection framework for Python projects. This library allows you to define services, manage their lifecycle, and inject dependencies into your applications in a clean and structured way.

Installation

You can install this library using pip:

pip install simple-dependency-injector

Basic Usage

Loading and Compiling Services

First, load your service definitions from a YAML file or Python module and compile them:

from simple_dependency_injector import DependencyInjector

# Create an injector and load the service definitions
injector = DependencyInjector(base_path='config_path')
injector.load('services.yaml')
injector.compile()

# Access a service
service = injector.get('my_service')

Service Definition Example (services.yaml)

You can define services in a YAML file:

services:
  my_service:
    class: 'tests/services/my_module.py#MyService'
    arguments:
      - '@another_service'
    scope: singleton

  another_service:
    class: 'tests/services/another_module.py#AnotherService'
    scope: transient

• class: The fully qualified class name to instantiate.

• arguments: The list of dependencies to inject.

  • Service Reference (@service_name): This resolves to another service defined in the injector.
  • Tagged Services (!tagged:tag_name): This resolves to a list of services that have the specified tag.
  • Context Reference (!context): This resolves to the current DI context.

• scope: The lifecycle of the service. Options are singleton, transient, request, or ambivalent.

Example of Argument Resolution:

services:
  my_service:
    class: 'tests/services/my_service.py#MyService'
    arguments:
      - '@another_service'
      - '!tagged:logging'
      - '!context'
    scope: singleton

When my_service is instantiated, the @another_service argument will resolve to the instance of another_service, !tagged:logging will resolve to a list of services tagged with logging, and !context will resolve to the current DI context.

Accessing Services by Tags

You can assign tags to services and resolve them by tag:

services:
  tagged_service:
    class: 'tests/services/tagged_service.py#TaggedService'
    tags:
      - 'my_tag'
    scope: singleton

You can then retrieve all services that have a specific tag:

services_with_tag = injector.get_list_with_tag('my_tag')

Linking Services

You can link services during runtime. For example, you can retrieve one service and assign its instance to another service:

injector.link('source_service', 'target_service')

This is useful when you need to dynamically replace or redirect service instances.

Using the Dependency Injector in Django

To use the dependency injector in Django, you can inject services into requests by creating a custom middleware.

1. Middleware for Dependency Injection Context

Create a middleware to add a new dependency injection context for each request:

# middlewares.py
from simple_dependency_injector import DependencyInjector

injector = DependencyInjector(base_path='config_path')
injector.load('services.yaml')
injector.compile()


class DependencyInjectorMiddleware:
  def __init__(self, get_response):
    self.get_response = get_response

  def __call__(self, request):
    request.container = injector.create_context()
    response = self.get_response(request)
    return response

2. Middleware for Logger Service

You can also create a middleware to inject services like a logger into the request context:

# middlewares.py
from .logger_service import DjangoLoggerService

class LoggerMiddleware:
    def __init__(self, get_response):
        self.get_response = get_response

    def __call__(self, request):
        request.container.set("logger_service", DjangoLoggerService(request))
        response = self.get_response(request)
        return response

3. Register the Middlewares in Django Settings

Add the middlewares to your MIDDLEWARE setting in settings.py:

# settings.py
MIDDLEWARE = [
    # Other middlewares
    'myapp.middlewares.DependencyInjectorMiddleware',
    'myapp.middlewares.LoggerMiddleware',
]

4. Accessing Services in Django Views

Now you can access the services from the request container in your Django views:

# views.py
from django.http import JsonResponse

def my_view(request):
    # Get the logger service from the DI container
    logger = request.container.get('logger_service')

    # Use the logger
    logger.log('This is a log message')

    return JsonResponse({'status': 'success'})

Advanced Features

Using Factories

You can define services using factory methods. This is useful when the service creation logic is more complex:

services:
  factory_service:
    factory:
      class: 'tests/services/my_module.py#MyFactory'
      method: create_service
    arguments:
      - 'config_value'
    scope: singleton

Contextual Dependency Injection

For services that need to maintain a request-specific state, you can create a new context per request and resolve services within that context:

# Create a context for each request
context = injector.create_context()

# Access services within that context
service = context.get('my_service')

Development

Setting Up a Development Environment

To set up a local development environment for this project, follow these steps:

1. Fork this repository and clone it:

git clone https://github.com/yourusername/python-simple-dependency-injector.git
cd simple-dependency-injector

1. Create a virtual environment:

python -m venv venv

1. Activate the virtual environment:

source venv/bin/activate

1. Install the development dependencies:

pip install -r requirements-dev.txt

Now you are ready to start working on the project. You can run tests, add new features, or fix bugs.

Check the code style

black simple_dependency_injector tests && pylint simple_dependency_injector tests

Tests

This project includes a suite of unit tests to ensure that all functionality works as expected. The tests are located in the tests directory, and you can run them using:

python -m unittest discover tests

License

This project is licensed under the MIT License. See the LICENSE file for details.