Lifespan context manager in FastAPI - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

What happens during the lifespan context manager in FastAPI?

Consider a FastAPI app using a lifespan context manager to open and close a database connection. What is the correct sequence of events when the app starts and stops?

FastAPI

from fastapi import FastAPI
from contextlib import asynccontextmanager

@asynccontextmanager
async def lifespan(app: FastAPI):
    print('Connecting to DB')
    yield
    print('Disconnecting from DB')

app = FastAPI(lifespan=lifespan)

A 1,2,3

B 2,1,3

C 1,3,2

D 3,1,2

💡 Hint

Think about what happens before and after the yield statement in a context manager.

The code before yield runs when the app starts, and the code after yield runs when the app stops.

❓ state_output

intermediate

What is printed when the FastAPI app with lifespan starts and stops?

Given this FastAPI app with a lifespan context manager, what will be printed to the console when the app starts and then stops?

FastAPI

from fastapi import FastAPI
from contextlib import asynccontextmanager

@asynccontextmanager
async def lifespan(app: FastAPI):
    print('Starting app')
    yield
    print('Stopping app')

app = FastAPI(lifespan=lifespan)

A Starting app\nStopping app

B Stopping app\nStarting app

C Starting app

D Stopping app

💡 Hint

Remember the lifespan context manager runs code before and after the yield.

The print before yield runs at startup, the print after yield runs at shutdown.

🔧 Debug

advanced

Why does this FastAPI lifespan context manager cause an error?

Examine this lifespan context manager code. Why does it raise a RuntimeError when the app starts?

FastAPI

from fastapi import FastAPI
from contextlib import asynccontextmanager

@asynccontextmanager
async def lifespan(app: FastAPI):
    print('Setup')
    # Missing yield statement
    print('Teardown')

app = FastAPI(lifespan=lifespan)

A It raises RuntimeError because the app variable is not used inside lifespan.

B It raises RuntimeError because print statements are not allowed in lifespan.

C It raises RuntimeError because FastAPI requires a synchronous lifespan function.

D It raises RuntimeError because the async context manager function does not yield.

💡 Hint

Async context managers must have exactly one yield.

Without a yield, the async context manager is invalid and raises RuntimeError.

📝 Syntax

advanced

Which lifespan context manager code is syntactically correct in FastAPI?

Choose the option with correct syntax for an async lifespan context manager in FastAPI.

A

from contextlib import contextmanager

@contextmanager
def lifespan(app: FastAPI):
    print('Start')
    yield
    print('End')

B

from contextlib import asynccontextmanager

def lifespan(app: FastAPI):
    print('Start')
    yield
    print('End')

C

from contextlib import asynccontextmanager

@asynccontextmanager
async def lifespan(app: FastAPI):
    print('Start')
    yield
    print('End')

D

from contextlib import asynccontextmanager

@asynccontextmanager
def lifespan():
    print('Start')
    yield
    print('End')

💡 Hint

FastAPI expects an async context manager with the app parameter.

Option C uses asynccontextmanager decorator, async function with app parameter, and yield.

🧠 Conceptual

expert

What is the main benefit of using a lifespan context manager in FastAPI?

Why would a developer use a lifespan context manager in a FastAPI application?

A To automatically reload the app when code changes are detected.

B To manage startup and shutdown tasks like opening and closing resources cleanly.

C To handle HTTP request routing and URL matching.

D To replace dependency injection for request handlers.

💡 Hint

Think about what happens when the app starts and stops.

Lifespan context managers allow running code at app startup and shutdown to manage resources.