Context lifecycle execution in Flask - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a Flask app instance.

Flask

from flask import Flask
app = Flask([1])

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

Aapp

B__name__

CFlask

DNone

Attempts:

3 left

💡 Hint

Common Mistakes

Using a string like 'app' instead of __name__

Passing None which causes errors

The Flask app instance requires the current module name, which is given by __name__.

2fill in blank

medium

Complete the code to define a route for the home page.

Flask

@app.route([1])
def home():
    return "Hello, Flask!"

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

A"/home"

B"home"

C"/"

D"index"

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'home' without a slash

Using '/home' which is a different URL

The root URL path is "/" for the home page route.

3fill in blank

hard

Fix the error in the code to run the Flask app only when the script is executed directly.

Flask

if [1] == '__main__':
    app.run()

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

A__name__

Bapp.name

Cmain

Dapp.__main__

Attempts:

3 left

💡 Hint

Common Mistakes

Using app.name which is incorrect

Using 'main' without underscores

The special variable __name__ equals '__main__' when the script runs directly.

4fill in blank

hard

Fill both blanks to access the request method inside a route function.

Flask

from flask import [1]

@app.route('/submit', methods=['POST'])
def submit():
    if [2].method == 'POST':
        return 'Form submitted!'

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

Arequest

BResponse

DFlask

Attempts:

3 left

💡 Hint

Common Mistakes

Importing Response instead of request

Using Flask instead of request

You import request from Flask and use it to check the HTTP method.

5fill in blank

hard

Fill all three blanks to create a context manager that pushes and pops the app context.

Flask

with app.[1]() as [2]:
    print([3].app.name)

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

Aapp_context

Bctx

Drequest

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'request' instead of 'ctx' for the context variable

Not using app_context() method

The app_context() method creates a context manager. Capture the context variable as ctx and access the app name with ctx.app.name.

Practice

1. What is the main purpose of Flask's before_request function in the context lifecycle?

easy

A. To run code before each request to prepare data or resources

B. To clean up resources after a request finishes

C. To handle errors during a request

D. To define the URL routes for the application

Solution

1. Step 1: Understand the role of before_request

   This function runs before each request to set up anything needed during the request.

2. Step 2: Compare with other lifecycle hooks

   after_request cleans up after requests, error handlers manage errors, and routes define URLs.

3. Final Answer:

   To run code before each request to prepare data or resources -> Option A

4. Quick Check:

   before_request runs before request [OK]

Hint: Remember: before_request runs setup code before handling requests [OK]

Common Mistakes:

• Confusing before_request with after_request
• Thinking before_request handles errors
• Mixing route definitions with lifecycle hooks

2. Which of the following is the correct way to store data for the current request using Flask's context?

easy

A. Store data in the g object inside a before_request function

B. Use a global variable outside the request

C. Save data in a class variable of the Flask app

D. Write data directly to the response object

Solution

1. Step 1: Identify how Flask manages request-specific data

   Flask provides the g object to store data unique to each request.

2. Step 2: Confirm correct usage

   Using g inside before_request ensures data is set up before route handlers run.

3. Final Answer:

   Store data in the g object inside a before_request function -> Option A

4. Quick Check:

   g stores request data [OK]

Hint: Use g for request data, not globals [OK]

Common Mistakes:

• Using global variables that persist across requests
• Trying to store request data in app class variables
• Modifying the response object directly for data storage

3. Given this Flask code snippet, what will be printed when a request is made to /hello?

from flask import Flask, g
app = Flask(__name__)

@app.before_request
def before():
    g.message = 'Hi'

@app.route('/hello')
def hello():
    return g.message + ' there!'

medium

A. there!

B. Error: g.message not set

C. Hi there!

D. Hi

Solution

1. Step 1: Analyze the before_request function

   The function sets g.message to 'Hi' before the route runs.

2. Step 2: Check the route handler output

   The route returns g.message + ' there!', which becomes 'Hi there!'.

3. Final Answer:

   Hi there! -> Option C

4. Quick Check:

   g.message set before route [OK]

Hint: before_request sets g data used in routes [OK]

Common Mistakes:

• Assuming g.message is not set yet
• Forgetting before_request runs before routes
• Expecting an error due to missing g attribute

4. What is wrong with this Flask code that tries to use g outside a request context?

from flask import Flask, g
app = Flask(__name__)

g.message = 'Hello'

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

medium

A. The g object cannot store strings

B. The route function is missing a return statement

C. The app is missing a secret key

D. Accessing g outside a request causes a runtime error

Solution

1. Step 1: Identify where g is assigned

   g.message = 'Hello' is set outside any request or app context.

2. Step 2: Understand Flask context rules

   g is only available during a request context; accessing it outside causes an error.

3. Final Answer:

   Accessing g outside a request causes a runtime error -> Option D

4. Quick Check:

   g only valid inside requests [OK]

Hint: Set g only inside request functions [OK]

Common Mistakes:

• Setting g variables globally outside requests
• Confusing g with global variables
• Ignoring Flask's context lifecycle rules

5. You want to log the time taken by each request in your Flask app. Which is the best way to do this using context lifecycle hooks?

hard

A. Use teardown_request to set start time and before_request to log duration

B. Use before_request to store start time in g, and after_request to calculate and log duration

C. Log the time only inside the route without lifecycle hooks

D. Store start time in a global variable and log it in the route function

Solution

1. Step 1: Use before_request to mark start time

   Store the current time in g.start_time before the request runs.

2. Step 2: Use after_request to calculate duration and log

   Calculate elapsed time using current time minus g.start_time and log it, then return the response.

3. Final Answer:

   Use before_request to store start time in g, and after_request to calculate and log duration -> Option B

4. Quick Check:

   Use before_request and after_request for timing [OK]

Hint: Start timer before, log after request finishes [OK]

Common Mistakes:

• Using global variables instead of g
• Logging time only inside routes missing full request duration
• Mixing up lifecycle hook order