Teardown hooks in Flask - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

What happens when a Flask teardown hook raises an exception?

Consider a Flask app with a teardown hook that raises an exception. What is the behavior of the app after a request finishes?

Flask

from flask import Flask
app = Flask(__name__)

@app.teardown_request
def teardown(exception):
    raise Exception('Error in teardown')

@app.route('/')
def index():
    return 'Hello World'

if __name__ == '__main__':
    app.run()

A The exception is logged but does not affect the response sent to the client.

B The exception causes the server to crash and no response is sent.

C The exception modifies the response body to include the error message.

D The exception is ignored silently without any logging.

💡 Hint

Think about how Flask handles errors in teardown hooks after the response is sent.

Flask runs teardown hooks after the response is sent. If a teardown hook raises an exception, Flask logs it but does not change the response or crash the server.

❓ state_output

intermediate

What is the output count of teardown calls after multiple requests?

Given this Flask app, how many times will the teardown function print 'Teardown called' after 3 requests to '/'?

Flask

from flask import Flask
app = Flask(__name__)

count = 0

@app.teardown_request
def teardown(exception):
    global count
    count += 1
    print('Teardown called')

@app.route('/')
def index():
    return 'Hi'

if __name__ == '__main__':
    app.run()

A 0

B 1

C 3

D 6

💡 Hint

Teardown hooks run once per request after the response.

The teardown function runs once after each request finishes, so after 3 requests it runs 3 times.

📝 Syntax

advanced

Which option correctly registers a teardown hook for the application context?

Select the correct way to register a teardown function that runs when the Flask application context ends.

A

@app.teardown_app_context
def teardown_appcontext(exception):
    print('App context teardown')

B

@app.teardown_request
def teardown_appcontext(exception):
    print('App context teardown')

C

@app.teardown
def teardown_appcontext(exception):
    print('App context teardown')

D

@app.teardown_appcontext
def teardown_appcontext(exception):
    print('App context teardown')

💡 Hint

Check the exact decorator name for application context teardown.

The correct decorator is @app.teardown_appcontext. The others are either for request teardown or invalid.

🔧 Debug

advanced

Why does this teardown hook not run after a request?

Identify the reason why the teardown function below never executes after requests.

Flask

from flask import Flask
app = Flask(__name__)

@app.teardown_request
def teardown():
    print('Teardown executed')

@app.route('/')
def index():
    return 'Hello'

if __name__ == '__main__':
    app.run()

A The decorator @app.teardown_request is invalid and should be @app.teardown.

B The teardown function must accept an exception argument even if unused.

C The function name 'teardown' is reserved and causes a conflict.

D Teardown functions only run on error responses, not successful ones.

💡 Hint

Check the function signature required by teardown_request hooks.

Teardown functions registered with @app.teardown_request must accept one argument (the exception), even if not used. Missing it prevents the function from running.

🧠 Conceptual

expert

What is the main difference between @app.teardown_request and @app.teardown_appcontext?

Choose the statement that best describes the difference between these two Flask teardown decorators.

A @app.teardown_request runs after each request; @app.teardown_appcontext runs when the app context ends, which may be less frequent.

B @app.teardown_request runs only on errors; @app.teardown_appcontext runs after every request.

C @app.teardown_request runs before the request starts; @app.teardown_appcontext runs after the request ends.

D @app.teardown_request and @app.teardown_appcontext are aliases and behave identically.

💡 Hint

Think about the lifecycle of a request versus the application context.

@app.teardown_request runs after each request finishes. @app.teardown_appcontext runs when the application context is popped, which can happen less often than requests.