Python lightweight dependency injection library

Last update: Dec 16, 2022

Overview

pythondi

pythondi is a lightweight dependency injection library for python

Support both sync and async functions

Installation

pip3 install pythondi

Usage

First, you have to binding classes to provider.

There is three different ways to binding.

Binding one by one

from pythondi import Provider


provider = Provider()
provider.bind(Repo, SQLRepo)
provider.bind(Usecase, CreateUsecase)

Binding at initialization

from pythondi import Provider


provider = Provider(cls=Repo, new_cls=SQLRepo)

Binding at initialization with dictionary

from pythondi import Provider


provider = Provider(classes={Repo: SQLRepo, Usecase: CreateUsecase})

After binding, you need to configure it to container

from pythondi import configure, configure_after_clear


# Inject with configure
configure(provider=provider)

# Or if you want to fresh inject, use `configure_after_clear`
configure_after_clear(provider=provider)

Import inject

from pythondi import inject

Add type annotations that you want to inject dependencies

class Usecase:
    def __init__(self, repo: Repo):
        self.repo = repo

Add decorator

class Usecase:
    @inject()
    def __init__(self, repo: Repo):
        self.repo = repo

Initialize class with no arguments

usecase = Usecase()

Or, you can also inject manually through decorator arguments

class Usecase:
    @inject(repo=SQLRepo)
    def __init__(self, repo):
        self.repo = repo

In this case, do not have to configure providers and type annotation.

For test

In case of test codes, you probably want to use mock objects.

In that case, you must use keyword arguments.

class MockRepo:
    pass


@inject()
def test(repo: Repo):
    return repo

Yes:

test(repo=MockRepo())

No:

test(MockRepo())
test(MockRepo)

Note

At the moment of inject, class is automatically initialized.

So you don't have to initialize your class inside of code.

Yes:

@inject()
def __init__(self, repo: Repo):
    self.repo = repo

No:

@inject()
def __init__(self, repo: Repo):
    self.repo = repo()

General example

import abc

from pythondi import Provider, configure, configure_after_clear, inject


class Repo:
    """Interface class"""
    __metaclass__ = abc.ABCMeta

    @abc.abstractmethod
    def get(self):
        pass


class SQLRepo(Repo):
    """Impl class"""
    def get(self):
        print('SQLRepo')


class Usecase:
    @inject()
    def __init__(self, repo: Repo):
        self.repo = repo


if __name__ == '__main__':
    # Init provider
    provider = Provider()

    # Bind `Impl` class to `Interface` class
    provider.bind(Repo, SQLRepo)

    # Inject with configure
    configure(provider=provider)

    # Or if you want to fresh injection, use `configure_after_clear`
    configure_after_clear(provider=provider)

    # Init class without arguments
    u = Usecase()

FastAPI example

from fastapi import FastAPI, APIRouter

from pythondi import Provider, configure, inject
import abc

router = APIRouter()


class Repo:
    """Interface class"""
    __metaclass__ = abc.ABCMeta

    @abc.abstractmethod
    def get(self):
        pass


class SQLRepo(Repo):
    """Impl class"""
    def __init__(self):
        pass

    def get(self):
        print('SQLRepo')


@router.route('/')
def home():
    usecase = Usecase()
    usecase.repo.get()
    return {'hello': 'world'}


class Usecase:
    @inject()
    def __init__(self, repo: Repo):
        self.repo = repo


def create_app():
    provider = Provider()
    provider.bind(Repo, SQLRepo)
    configure(provider=provider)
    app = FastAPI()
    app.include_router(router)
    return app


if __name__ == '__main__':
    app = create_app()
    app.run(debug=True)

Flask example

from flask import Flask, Blueprint, jsonify

from pythondi import Provider, configure, inject
import abc

bp = Blueprint('home', __name__)


class Repo:
    """Interface class"""
    __metaclass__ = abc.ABCMeta

    @abc.abstractmethod
    def get(self):
        pass


class SQLRepo(Repo):
    """Impl class"""
    def __init__(self):
        pass

    def get(self):
        print('SQLRepo')


@bp.route('/')
def home():
    usecase = Usecase()
    usecase.repo.get()
    return jsonify({'hello': 'world'})


class Usecase:
    @inject()
    def __init__(self, repo: Repo):
        self.repo = repo


def create_app():
    provider = Provider()
    provider.bind(Repo, SQLRepo)
    configure(provider=provider)
    app = Flask(__name__)
    app.register_blueprint(bp)
    return app


if __name__ == '__main__':
    app = create_app()
    app.run(debug=True)

Sanic example

import abc

from sanic import Sanic, Blueprint
from sanic.response import json

from pythondi import Provider, configure, inject


class Repo:
    """Interface class"""
    __metaclass__ = abc.ABCMeta

    @abc.abstractmethod
    def get(self):
        pass


class SQLRepo(Repo):
    """Impl class"""
    def __init__(self):
        pass

    def get(self):
        print('SQLRepo')


bp = Blueprint('home', url_prefix='/')


@bp.route('/')
async def home(request):
    usecase = Usecase()
    usecase.repo.get()
    return json({'hello': 'world'})


class Usecase:
    @inject()
    def __init__(self, repo: Repo):
        self.repo = repo


def create_app():
    provider = Provider()
    provider.bind(Repo, SQLRepo)
    configure(provider=provider)
    app = Sanic(__name__)
    app.blueprint(bp)
    return app


if __name__ == '__main__':
    app = create_app()
    app.run(debug=True)

Django example

"""
In case of django, just put the initializing code inside of django startup

You can use project folder's __init__.py or urls.py
"""

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Comments

Clean a polluted state to fix a flaky test.
What is the purpose of the change

This PR is to fix a flaky test tests/test_configure.py::test_configure, which can fail after running tests/test_container.py::test_set.

Reproduce the test failure

Run the following command:

python -m pytest tests/test_container.py::test_set tests/test_configure.py::test_configure

Expected Result

tests/test_configure.py::test_configure pass after running tests/test_container.py::test_set.

Actual Result

provider = <pythondi.Provider object at 0x7fa83b0b46d0> def configure(provider: Provider) -> Optional[NoReturn]: """Configure provider to container""" with _LOCK: if Container.get(): > raise InjectException(msg="Already injected") E pythondi.InjectException: Already injected pythondi/__init__.py:76: InjectException

Why it fails

The container is polluted after tests/test_container.py::test_set is run.

Fix

Clear the container at the beginning of tests/test_configure.py::test_configure.
opened by sturmianseq 1
Reset `Container` to a clean state
The PR aims to improve the reliability of the test test_configure by resetting Container to a clean state by calling methodclear.

The test can fail in the following way if Container is not in a clean state:

> raise InjectException(msg="Already injected") E pythondi.InjectException: Already injected
opened by sturmianseq 1