G object for request-scoped data in Flask - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

What is the output of this Flask route using g?

Consider this Flask route that uses the g object to store data during a request. What will be the output when accessing /show?

Flask

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

@app.before_request
def before():
    g.user = 'Alice'

@app.route('/show')
def show():
    return f"User is {g.user}"

A User is Alice

B AttributeError: 'g' object has no attribute 'user'

C KeyError: 'user'

D User is None

💡 Hint

Remember that g is used to store data during a request and is reset for each request.

The g object is a special Flask object used to store data during a request. Here, g.user is set to 'Alice' before the request, so the route returns 'User is Alice'.

❓ state_output

intermediate

What happens to g data across multiple requests?

If you set g.value = 10 in one request, what will g.value be in the next request if not set again?

Flask

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

@app.route('/set')
def set_value():
    g.value = 10
    return 'Value set'

@app.route('/get')
def get_value():
    return str(getattr(g, 'value', 'No value'))

A No value

B AttributeError

C 10

D 0

💡 Hint

Think about how Flask handles the g object for each request.

The g object is unique to each request. Data set in one request is not saved for the next. So, g.value is not set in the second request and returns 'No value'.

🔧 Debug

advanced

Why does this code raise RuntimeError when accessing g?

This Flask app tries to access g.user outside a request context. What causes the error?

Flask

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

def get_user():
    return g.user

print(get_user())

A Because <code>g</code> is a global variable accessible anytime

B Because <code>g.user</code> was never set

C Because <code>g</code> is only available during a request context

D Because Flask app is not running

💡 Hint

Think about when Flask creates the g object.

The g object exists only during an active request context. Accessing it outside a request (like in global code) raises a RuntimeError.

🧠 Conceptual

advanced

What is the main purpose of Flask's g object?

Choose the best description of what the g object is used for in Flask.

A To store data that lasts across multiple requests and users

B To manage database connections globally

C To store configuration settings for the Flask app

D To store data during a single request, accessible across functions

💡 Hint

Think about the lifespan of data stored in g.

The g object is designed to hold data during one request only. It helps share information between functions during that request.

📝 Syntax

expert

Which option correctly sets and accesses g data in Flask?

Select the option that correctly sets g.user in a before_request function and accesses it in a route.

A

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

def before():
    g.user = 'Bob'

@app.route('/')
def index():
    return f"User: {g.user}"

B

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

@app.before_request
def before():
    g.user = 'Bob'

@app.route('/')
def index():
    return f"User: {g.user}"

C

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

@app.before_request
def before():
    user = 'Bob'

@app.route('/')
def index():
    return f"User: {g.user}"

D

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

@app.before_request
def before():
    g.user = 'Bob'

@app.route('/')
def index():
    return f"User: {user}"

💡 Hint

Remember to use the @app.before_request decorator and access g.user properly.

Option B correctly sets g.user in a function decorated with @app.before_request and accesses it in the route. Other options either miss the decorator or use undefined variables.