G object for request-scoped data in Flask - Mini Project: Build & Apply

Using Flask's g Object for Request-Scoped Data

📖 Scenario: You are building a simple Flask web app that needs to store and access data specific to each web request. This data should be available throughout the request but reset for the next request.

🎯 Goal: Learn how to use Flask's g object to store and access request-scoped data safely and easily.

📋 What You'll Learn

Create a Flask app with a route

Use the g object to store data during a request

Access the stored data later in the same request

Demonstrate that data is reset for each new request

💡 Why This Matters

🌍 Real World

Web apps often need to keep track of user info or other data during a single web request without mixing it with other requests. Flask's <code>g</code> object is perfect for this.

💼 Career

Understanding request-scoped data is essential for backend web development with Flask, helping you write clean, safe, and maintainable code.

1

Set up a basic Flask app with a route

Import Flask from flask and create a Flask app called app. Then define a route / with a function index that returns the string 'Hello, Flask!'.

Flask

# Your code here

Need a hint?

Start by importing Flask and creating an app instance. Then add a route decorator and a simple function that returns a greeting.

2

Import g and store data in it

Import g from flask. Inside the index function, set g.user to the string 'Alice' to simulate storing user data for this request.

Flask

from flask import Flask, g

app = Flask(__name__)

@app.route('/')
def index():
    # Store user name in g
    # Your code here
    return 'Hello, Flask!'

Need a hint?

Remember to import g from flask. Then assign the user name to g.user inside the route function.

3

Access the stored g.user data in the response

Modify the index function to return a greeting that includes the user name stored in g.user. Use an f-string to return f'Hello, {g.user}!'.

Flask

from flask import Flask, g

app = Flask(__name__)

@app.route('/')
def index():
    g.user = 'Alice'
    # Return greeting with g.user
    # Your code here

Need a hint?

Use an f-string to include g.user in the returned string.

4

Add a before_request function to set g.user

Define a function load_user decorated with @app.before_request that sets g.user to 'Alice'. Remove the g.user assignment from the index function.

Flask

from flask import Flask, g

app = Flask(__name__)

@app.before_request
def load_user():
    # Set g.user here
    # Your code here

@app.route('/')
def index():
    # Remove g.user assignment here
    return f'Hello, {g.user}!'

Need a hint?

Use @app.before_request to run code before each request. Set g.user there so it is available in all routes.