Flask-DI

A minimal and clean FastAPI-style dependency injection system for Flask.

Features

• FastAPI-style Depends()
• Automatic injection (no decorators required)
• Nested dependencies
• Override system for testing
• Per-request caching
• Pure Python and lightweight

Installation

pip install di-flask

Usage

Note

For automatic injection of dependecies we need to wrap Flask class

from flask_di import DIFlask, Depends

app = DIFlask(__name__)

def get_db():
    return {"session": "db-session"}

def get_user(db=Depends(get_db)):
    return {"username": "alice", "db": db}

@app.route("/info")
def info(user=Depends(get_user)):
    return user

Tip

Flask-DI also supports Annotated type alias for declaring dependecies just like FastAPI does.

from flask_di import DIFlask, Depends
from typing import Annotated

app = DIFlask(__name__)

def get_db():
    return {"session": "db-session"}

SessionDep = Annotated(dict, Depends(get_db))

def get_user(session: SessionDep):
    return {"username": "alice", "session": session}

UserDep = Annotated(dict, Depends(get_user))

@app.route("/info")
def info(user: UserDep):
    return user

Overrides

Flask-DI supports overrides for easy mocking and testing of dependacies.

def override_db():
    return {"session": "test-db"}

app.dependency_overrides[get_db] = override_db

Disclaimer

This is my snippet of code that I use for my Flask project.

Just wanted to share as its dead simple, lightweight and pure python.

Contribution

You are free to contribute to the project in any way you want.

The goal of the project is to be on-par with FastAPI DI style. Please keep it simple, concise and with clear code comments.