Teardown hooks in Flask - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to register a teardown function in Flask.

Flask

from flask import Flask
app = Flask(__name__)

@app.[1]()
def cleanup(exception=None):
    print("Cleaning up after request")

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

Abefore_request

Bteardown_request

Croute

Dafter_request

Attempts:

3 left

💡 Hint

Common Mistakes

Using @app.before_request instead of @app.teardown_request

Using @app.after_request which does not run on exceptions

The @app.teardown_request decorator registers a function to run after each request, even if an exception occurs.

2fill in blank

medium

Complete the code to access the exception object in a teardown function.

Flask

@app.teardown_request
def cleanup([1]=None):
    if [1]:
        print(f"Exception occurred: [1]")

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

Aexception=None

Bexception

Cexc

Derror

Attempts:

3 left

💡 Hint

Common Mistakes

Not providing a default value for the exception argument

Using a different argument name without default

The teardown function receives an optional exception argument which is None if no error occurred.

3fill in blank

hard

Fix the error in the teardown function registration.

Flask

def cleanup(exception=None):
    print("Cleaning up")

app.[1](cleanup)

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

Abefore_request

Bafter_request

Cteardown_request

Droute

Attempts:

3 left

💡 Hint

Common Mistakes

Using app.before_request(cleanup) instead

Using app.route(cleanup) which is for URL routes

To register a teardown function, use app.teardown_request decorator or call app.teardown_request(cleanup).

4fill in blank

hard

Fill both blanks to create a teardown function that closes a database connection.

Flask

@app.[1]()
def close_db([2]=None):
    db = getattr(g, 'db', None)
    if db is not None:
        db.close()

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

Ateardown_request

Bbefore_request

Cexception

Derror

Attempts:

3 left

💡 Hint

Common Mistakes

Using before_request decorator

Using wrong argument name like error

The teardown function uses @app.teardown_request and receives an exception argument.

5fill in blank

hard

Fill all three blanks to register a teardown function that logs errors and cleans up resources.

Flask

@app.[1]()
def teardown([2]=None):
    if [2]:
        app.logger.error(f"Error: [2]")
    cleanup_resources()

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

Ateardown_request

Bexception

Dbefore_request

Attempts:

3 left

💡 Hint

Common Mistakes

Using before_request decorator

Not using the exception argument properly

The function is decorated with @app.teardown_request and uses the exception argument to check for errors.

Practice

1. What is the main purpose of a teardown_request function in Flask?

easy

A. To handle incoming HTTP requests

B. To define URL routes

C. To start a new request

D. To run cleanup code after each request finishes

Solution

1. Step 1: Understand the role of teardown hooks

   Teardown hooks run after a request ends to clean up resources like files or database connections.

2. Step 2: Match the purpose with options

   Only To run cleanup code after each request finishes describes running cleanup code after each request finishes, which matches the teardown hook purpose.

3. Final Answer:

   To run cleanup code after each request finishes -> Option D

4. Quick Check:

   Teardown hooks = cleanup after request [OK]

Hint: Teardown hooks always run after request ends [OK]

Common Mistakes:

• Confusing teardown with request handling
• Thinking teardown runs before request
• Assuming teardown defines routes

2. Which of the following is the correct way to register a teardown function in Flask?

easy

A. @app.teardown_request
def cleanup(error=None): pass

B. @app.after_request
def cleanup(): pass

C. @app.route('/teardown')
def cleanup(): pass

D. @app.before_request
def cleanup(): pass

Solution

1. Step 1: Identify the correct decorator for teardown

   The correct decorator to register a teardown function is @app.teardown_request, which optionally accepts an error parameter.

2. Step 2: Check function signature

   The function should accept an optional error=None parameter to detect errors during the request.

3. Final Answer:

   @app.teardown_request\ndef cleanup(error=None): pass -> Option A

4. Quick Check:

   Teardown decorator = @app.teardown_request [OK]

Hint: Teardown functions use @app.teardown_request with error param [OK]

Common Mistakes:

• Using @app.before_request instead
• Missing the optional error parameter
• Confusing with @app.after_request

3. Given this Flask code snippet, what will be printed after a request completes successfully (no error)?

@app.teardown_request
def cleanup(error=None):
    if error:
        print('Error occurred')
    else:
        print('Request finished cleanly')

medium

A. Error occurred

B. Request finished cleanly

C. No output

D. SyntaxError

Solution

1. Step 1: Understand the error parameter in teardown

   The error parameter is None if the request finished without errors.

2. Step 2: Trace the if-else logic

   Since error is None, the else branch runs, printing 'Request finished cleanly'.

3. Final Answer:

   Request finished cleanly -> Option B

4. Quick Check:

   error=None means clean finish [OK]

Hint: error=None means no error, so else branch runs [OK]

Common Mistakes:

• Assuming error is always True
• Expecting no output
• Confusing teardown with before_request

4. What is wrong with this teardown function?

@app.teardown_request
def cleanup():
    print('Cleaning up')

medium

A. Decorator should be @app.before_request

B. Using print inside teardown is not allowed

C. Missing the optional error parameter in the function

D. Function name must be 'teardown' exactly

Solution

1. Step 1: Check teardown function signature

   Teardown functions must accept an optional error=None parameter to receive error info.

2. Step 2: Identify missing parameter issue

   The function cleanup has no parameters, so Flask will raise an error when calling it.

3. Final Answer:

   Missing the optional error parameter in the function -> Option C

4. Quick Check:

   Teardown needs error param or it fails [OK]

Hint: Teardown functions must accept error=None parameter [OK]

Common Mistakes:

• Omitting error parameter
• Using wrong decorator
• Thinking function name is fixed

5. You want to close a database connection after every request, but only if it was opened during that request. Which is the best way to do this using a teardown hook?

hard

A. Use @app.teardown_request with a function that checks if the connection exists and closes it

B. Use @app.before_request to close the connection before the request starts

C. Use @app.route to close the connection on a specific URL

D. Use @app.after_request to close the connection without checking if it exists

Solution

1. Step 1: Understand when to close resources

   Resources like database connections should be closed after the request ends, not before or on specific routes.

2. Step 2: Use teardown_request with conditional check

   The teardown function can check if the connection was opened during the request and close it safely.

3. Final Answer:

   Use @app.teardown_request with a function that checks if the connection exists and closes it -> Option A

4. Quick Check:

   Teardown + check connection before closing = best practice [OK]

Hint: Close resources in teardown only if they exist [OK]

Common Mistakes:

• Closing connection before request starts
• Closing without checking if connection exists
• Trying to close on specific route only