G object for request-scoped data in Flask - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to import the Flask global object used for request-scoped data.

Flask

from flask import [1]

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

Ag

Brequest

Csession

Dapp

Attempts:

3 left

💡 Hint

Common Mistakes

Importing request instead of g.

Using session which is for user sessions, not request data.

The g object in Flask is used to store data during a request. Import it from flask.

2fill in blank

medium

Complete the code to store a value in the Flask g object during a request.

Flask

from flask import g

def before_request():
    g.[1] = 'user123'

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

Auser_id

Bsession_id

Capp_name

Drequest_data

Attempts:

3 left

💡 Hint

Common Mistakes

Using session_id which is not typically stored in g.

Using unrelated names like app_name.

You can add any attribute to g. Here, user_id is a common example to store user info during a request.

3fill in blank

hard

Fix the error in accessing the g object attribute inside a view function.

Flask

from flask import g

@app.route('/')
def index():
    user = g.[1]
    return f"Hello, {user}!"

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

Auserid

BuserId

CUser_id

Duser_id

Attempts:

3 left

💡 Hint

Common Mistakes

Using camelCase or different casing like userId or User_id.

Using all lowercase but missing underscore like userid.

Attribute names in g are case-sensitive. If you stored user_id, you must access it exactly as g.user_id.

4fill in blank

hard

Fill both blanks to correctly check if an attribute exists in g and use it.

Flask

from flask import g

@app.route('/profile')
def profile():
    if hasattr(g, '[1]'):
        user = getattr(g, '[2]')
    else:
        user = 'Guest'
    return f"Profile: {user}"

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

Auser_id

Busername

Cuser

Dprofile_id

Attempts:

3 left

💡 Hint

Common Mistakes

Using different attribute names in hasattr and getattr.

Using attribute names not set in g.

To safely access an attribute in g, check with hasattr and then get it with getattr using the same attribute name.

5fill in blank

hard

Fill both blanks to create a dictionary comprehension that stores lengths of strings in g if length is greater than 3.

Flask

from flask import g

words = ['apple', 'bat', 'carrot']
g.lengths = {word: len(word) for word in words if len(word) [1] 3 and 'a' [2] word}

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

A:

B>

Cin

D==

Attempts:

3 left

💡 Hint

Common Mistakes

Using = instead of : in dictionary comprehension.

Using == instead of > for length comparison.

Using == instead of in to check substring presence.

The dictionary comprehension needs a colon : between key and value, a greater than sign > to check length, and in to check if 'a' is in the word.

Practice

1. What is the main purpose of the g object in Flask?

easy

A. To store data temporarily during a single request

B. To store data permanently across all requests

C. To manage database connections globally

D. To handle user sessions across multiple requests

Solution

1. Step 1: Understand the scope of g

   The g object is designed to hold data only during the life of one request.

2. Step 2: Compare with other storage options

   Unlike session or global variables, g does not persist data beyond the current request.

3. Final Answer:

   To store data temporarily during a single request -> Option A

4. Quick Check:

   g = request-scoped storage [OK]

Hint: Remember: g lasts only for one request [OK]

Common Mistakes:

• Thinking g stores data across requests
• Confusing g with session or global variables
• Assuming g manages database connections automatically

2. Which of the following is the correct way to store a value in the g object inside a Flask view function?

easy

A. g.user = 'Alice'

B. g.add('user', 'Alice')

C. g.set('user', 'Alice')

D. g['user'] = Alice

Solution

1. Step 1: Recall how to assign attributes in g

   g acts like a simple object where you assign attributes using dot notation.

2. Step 2: Check each option's syntax

   g.user = 'Alice' uses g.user = 'Alice', which is the correct way. g['user'] = Alice uses dictionary style which is invalid. Options B and C use methods that g does not have.

3. Final Answer:

   g.user = 'Alice' -> Option A

4. Quick Check:

   Use dot notation to set g attributes [OK]

Hint: Use dot notation: g.attribute = value [OK]

Common Mistakes:

• Using dictionary syntax like g['key']
• Trying to call non-existent methods on g
• Confusing g with Flask's session object

3. Consider this Flask code snippet:

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

@app.before_request
def before():
    g.value = 10

@app.route('/')
def index():
    g.value += 5
    return str(g.value)

What will be the output when you visit the '/' route?

medium

A. 10

B. 5

C. 15

D. Error: AttributeError

Solution

1. Step 1: Understand the before_request function

   Before each request, g.value is set to 10.

2. Step 2: Analyze the index function

   It adds 5 to g.value, making it 15, then returns it as a string.

3. Final Answer:

   15 -> Option C

4. Quick Check:

   g.value starts 10, adds 5 = 15 [OK]

Hint: Remember g resets each request; additions apply after setup [OK]

Common Mistakes:

• Assuming g.value keeps old values between requests
• Forgetting before_request runs before route
• Expecting an error due to missing attribute

4. What is wrong with this Flask code using g?

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

@app.route('/')
def index():
    if not hasattr(g, 'counter'):
        g.counter = 0
    g.counter += 1
    return str(g.counter)

medium

A. It will raise an error because g cannot have new attributes

B. The code will cause a syntax error due to missing import

C. The counter will increase across requests, causing unexpected results

D. The counter resets on every request, so it always returns 1

Solution

1. Step 1: Understand g scope

   g is reset for each request, so counter does not persist between requests.

2. Step 2: Analyze the counter behavior

   Each request starts fresh, so counter is set to 0 then incremented to 1 every time.

3. Final Answer:

   The counter resets on every request, so it always returns 1 -> Option D

4. Quick Check:

   g data is request-scoped, no persistence [OK]

Hint: Remember g resets each request; no data persists [OK]

Common Mistakes:

• Expecting g.counter to keep increasing across requests
• Thinking g forbids new attributes
• Confusing g with session or global variables

5. You want to share a database connection during a single Flask request using g. Which code snippet correctly opens the connection once per request and reuses it in multiple functions?

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

def get_db():
    if not hasattr(g, 'db'):
        g.db = open_database_connection()
    return g.db

@app.route('/')
def index():
    db = get_db()
    # use db
    return 'OK'

What is the main benefit of this pattern?

hard

A. It opens a new database connection on every function call

B. It shares one connection per request, avoiding multiple opens

C. It stores the connection globally for all requests

D. It closes the connection automatically after each function

Solution

1. Step 1: Analyze the get_db function

   It checks if g.db exists; if not, it opens the connection and saves it to g.

2. Step 2: Understand request scope of g

   The connection is stored only for the current request, so multiple calls reuse the same connection.

3. Step 3: Compare options

   It shares one connection per request, avoiding multiple opens correctly describes this behavior. It opens a new database connection on every function call is wrong because it avoids multiple opens. It stores the connection globally for all requests is wrong because g is not global. It closes the connection automatically after each function is incorrect; closing is not automatic here.

4. Final Answer:

   It shares one connection per request, avoiding multiple opens -> Option B

5. Quick Check:

   Use g to cache per-request resources [OK]

Hint: Cache resources in g to reuse during request [OK]

Common Mistakes:

• Thinking g stores data globally across requests
• Opening new connections on every function call
• Assuming g auto-closes resources