Lifespan context manager in FastAPI - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to import the asynccontextmanager decorator used for lifespan from contextlib.

FastAPI

from contextlib import [1]

Drag options to blanks, or click blank then click option'

AFastAPI

Basynccontextmanager

CRequest

DDepends

Attempts:

3 left

💡 Hint

Common Mistakes

Importing FastAPI instead of asynccontextmanager

Importing unrelated classes like Request or Depends

The asynccontextmanager decorator is imported from contextlib to define a lifespan context manager.

2fill in blank

medium

Complete the code to define an async lifespan context manager function named 'lifespan'.

FastAPI

@asynccontextmanager
async def [1]():
    print('Starting app')
    yield
    print('Shutting down app')

Drag options to blanks, or click blank then click option'

Ashutdown

Bapp

Cstartup

Dlifespan

Attempts:

3 left

💡 Hint

Common Mistakes

Naming the function differently than lifespan

Forgetting to use yield inside the function

The async function decorated with @asynccontextmanager should be named lifespan by convention for the lifespan context manager.

3fill in blank

hard

Fix the error in the code to create a FastAPI app using the lifespan context manager.

FastAPI

app = FastAPI(lifespan=[1])

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Alifespan

Blifespan()

Clifespan_manager

Dlifespan_context

Attempts:

3 left

💡 Hint

Common Mistakes

Calling the lifespan function instead of passing it

Passing a wrong variable name

The lifespan argument expects the function itself, not a call to it.

4fill in blank

hard

Fill both blanks to correctly use the lifespan context manager with async code.

FastAPI

from contextlib import [1]

@[2]
async def lifespan():
    print('App starting')
    yield
    print('App shutting down')

Drag options to blanks, or click blank then click option'

Aasynccontextmanager

Blifespan

Ccontextmanager

Dapp

Attempts:

3 left

💡 Hint

Common Mistakes

Using synchronous contextmanager instead of asynccontextmanager

Using wrong decorator name

Use asynccontextmanager from contextlib and decorate the function with @asynccontextmanager to define an async lifespan context manager.

5fill in blank

hard

Fill all three blanks to create a FastAPI app with a lifespan context manager that prints messages on startup and shutdown.

FastAPI

from contextlib import [1]
from fastapi import FastAPI

@[2]
async def lifespan():
    print('Starting')
    yield
    print('Stopping')

app = FastAPI([3]=lifespan)

Drag options to blanks, or click blank then click option'

Aasynccontextmanager

Clifespan

Dstartup

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'startup' instead of 'lifespan' as argument

Not importing asynccontextmanager

Not decorating the function properly

Import asynccontextmanager from contextlib, decorate the async function lifespan with @asynccontextmanager, and pass it as the lifespan argument to FastAPI.

Practice

1. What is the main purpose of the lifespan context manager in a FastAPI application?

easy

A. To manage user authentication and authorization

B. To handle HTTP requests and responses

C. To define API routes and endpoints

D. To run setup code when the app starts and cleanup code when it stops

Solution

1. Step 1: Understand the role of lifespan context manager

   The lifespan context manager is designed to run code at the start and end of the FastAPI app lifecycle.

2. Step 2: Identify its main use

   It is used to set up resources like database connections when the app starts and clean them up when the app stops.

3. Final Answer:

   To run setup code when the app starts and cleanup code when it stops -> Option D

4. Quick Check:

   Lifespan manages startup and shutdown code = A [OK]

Hint: Lifespan runs code at app start and stop [OK]

Common Mistakes:

• Confusing lifespan with route handling
• Thinking lifespan manages HTTP requests
• Assuming lifespan handles user sessions

2. Which of the following is the correct way to define a lifespan context manager in FastAPI?

easy

A. async def lifespan(app): yield

B. def lifespan(): return app

C. async def lifespan(): return app

D. def lifespan(app): yield

Solution

1. Step 1: Recall lifespan signature

   The lifespan function must be async and accept the app parameter to manage startup and shutdown.

2. Step 2: Confirm use of yield

   Using yield inside the async function allows running code before and after the yield for startup and shutdown.

3. Final Answer:

   async def lifespan(app): yield -> Option A

4. Quick Check:

   Async + app param + yield = A [OK]

Hint: Lifespan is async with app param and uses yield [OK]

Common Mistakes:

• Forgetting async keyword
• Missing app parameter
• Using return instead of yield

3. Given this FastAPI lifespan code snippet, what will be printed when the app starts and stops?

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

medium

A. Only 'Starting app' is printed

B. 'Starting app' prints on start, 'Stopping app' prints on shutdown

C. Only 'Stopping app' is printed

D. Neither message is printed

Solution

1. Step 1: Understand yield in lifespan

   The code before yield runs at startup, and code after yield runs at shutdown.

2. Step 2: Match prints to lifecycle events

   So 'Starting app' prints when app starts, and 'Stopping app' prints when app stops.

3. Final Answer:

   'Starting app' prints on start, 'Stopping app' prints on shutdown -> Option B

4. Quick Check:

   Code before yield = start, after yield = stop [OK]

Hint: Code before yield runs on start, after yield on stop [OK]

Common Mistakes:

• Thinking both prints run immediately
• Assuming yield blocks all prints
• Confusing start and stop timing

4. What is wrong with this lifespan context manager code?

async def lifespan(app):
    print('Starting')
    return
    print('Stopping')

medium

A. The app parameter is not used, causing runtime error

B. Missing async keyword causes syntax error

C. Using return instead of yield prevents shutdown code from running

D. Print statements are not allowed in lifespan functions

Solution

1. Step 1: Identify use of return instead of yield

   The lifespan function must use yield to separate startup and shutdown code.

2. Step 2: Understand effect of return

   Using return exits the function immediately, so shutdown code after it never runs.

3. Final Answer:

   Using return instead of yield prevents shutdown code from running -> Option C

4. Quick Check:

   Return exits early; yield separates start/stop [OK]

Hint: Use yield, not return, to run shutdown code [OK]

Common Mistakes:

• Confusing return and yield in async functions
• Ignoring that shutdown code runs after yield
• Assuming print statements cause errors

5. You want to open a database connection when your FastAPI app starts and close it when the app stops using the lifespan context manager. Which code correctly implements this?

hard

A. async def lifespan(app):
db = await connect_db()
app.state.db = db
yield
await db.close()

B. async def lifespan(app):
db = await connect_db()
yield
app.state.db = db
await db.close()

C. def lifespan(app):
db = connect_db()
app.state.db = db
yield
db.close()

D. async def lifespan():
db = await connect_db()
app.state.db = db
yield
await db.close()

Solution

1. Step 1: Confirm async function with app parameter

   The lifespan function must be async and accept the app parameter to store the db connection.

2. Step 2: Check order of operations

   Connect to the database before yield, store it on app.state, then close it after yield.

3. Step 3: Verify correct use of await and yield

   Await connect_db and db.close, yield separates startup and shutdown code.

4. Final Answer:

   async def lifespan(app): db = await connect_db() app.state.db = db yield await db.close() -> Option A

5. Quick Check:

   Async + app param + yield + await connect/close = D [OK]

Hint: Connect before yield, close after, store in app.state [OK]

Common Mistakes:

• Placing yield before storing db connection
• Missing async or await keywords
• Not passing app parameter to lifespan