Dependency Injection in Python

From the FastAPI cheat sheet · Dependencies · verified Jul 2026

Dependency Injection

Share logic across endpoints using Depends().

python

from fastapi import Depends

async def get_db():
    db = SessionLocal()
    try:
        yield db
    finally:
        db.close()

@app.get("/items/")
async def read_items(db: Session = Depends(get_db)):
    return db.query(Item).all()

💡 Dependencies with yield run cleanup code after the response — perfect for DB sessions

⚡ Sub-dependencies chain automatically: get_admin_user → get_current_user → oauth2_scheme

📌 Use Depends() without arguments on a class to use it directly as a dependency

🟢 Global dependencies apply to every route — great for API key verification

dependenciesdependsinjection

Back to the full FastAPI cheat sheet