Lifespan context manager in FastAPI - Mini Project: Build & Apply

Using Lifespan Context Manager in FastAPI

📖 Scenario: You are building a simple FastAPI web application that needs to perform setup and cleanup tasks when the app starts and stops. This is common when connecting to databases or opening files.

🎯 Goal: Learn how to use the lifespan context manager in FastAPI to run code during app startup and shutdown.

📋 What You'll Learn

Create a FastAPI app instance

Define a lifespan context manager function

Use asynccontextmanager from contextlib

Print messages on startup and shutdown inside the lifespan

Use the lifespan context manager when creating the FastAPI app

💡 Why This Matters

🌍 Real World

Many web applications need to initialize resources like database connections or caches when they start, and clean them up when they stop. The lifespan context manager in FastAPI helps manage these tasks cleanly.

💼 Career

Understanding how to manage app startup and shutdown is important for backend developers working with FastAPI or similar frameworks to ensure reliable and maintainable services.

1

Create the FastAPI app instance

Import FastAPI from fastapi and create a variable called app that is an instance of FastAPI().

FastAPI

# Import FastAPI and create app instance
# Your code here

Need a hint?

Use from fastapi import FastAPI and then app = FastAPI().

2

Define the lifespan context manager function

Import asynccontextmanager from contextlib. Define an async function called lifespan that uses the @asynccontextmanager decorator. Inside it, print "Starting up...", then yield, then print "Shutting down...".

FastAPI

from fastapi import FastAPI
from contextlib import asynccontextmanager

app = FastAPI()

# Define lifespan context manager function
# Your code here

Need a hint?

Use @asynccontextmanager to decorate an async function named lifespan. Print before and after yield.

3

Use the lifespan context manager in the FastAPI app

Modify the app variable to pass the lifespan function as the lifespan parameter when creating the FastAPI instance.

FastAPI

from fastapi import FastAPI
from contextlib import asynccontextmanager

# Pass lifespan to FastAPI app
app = FastAPI()

@asynccontextmanager
async def lifespan(app: FastAPI):
    print("Starting up...")
    yield
    print("Shutting down...")

# Your code here

Need a hint?

Pass lifespan=lifespan when creating the FastAPI app.

4

Add a simple route to test the app

Add a route to app using the @app.get("/") decorator. Define an async function called read_root that returns a dictionary with {"message": "Hello World"}.

FastAPI

from fastapi import FastAPI
from contextlib import asynccontextmanager

@asynccontextmanager
async def lifespan(app: FastAPI):
    print("Starting up...")
    yield
    print("Shutting down...")

app = FastAPI(lifespan=lifespan)

# Add a GET route for '/' that returns a welcome message
# Your code here

Need a hint?

Use @app.get("/") and define async def read_root() returning the dictionary.