Before_request hooks in Flask - Mini Project: Build & Apply

Using Before_request Hooks in Flask

📖 Scenario: You are building a simple Flask web app that needs to check if a user is logged in before allowing access to certain pages.To do this, you will use a before_request hook to run a function before every request. This function will check a variable to decide if the user is logged in.

🎯 Goal: Create a Flask app that uses a before_request hook to check a login status before serving pages.If the user is not logged in, the app should redirect them to a login page.

📋 What You'll Learn

Create a Flask app instance

Define a global variable logged_in set to False

Use @app.before_request to define a function that checks logged_in

Redirect to /login if logged_in is False

Create two routes: / for the home page and /login for the login page

💡 Why This Matters

🌍 Real World

Before_request hooks are used in web apps to run code before every page loads, such as checking if a user is logged in or setting up data.

💼 Career

Understanding before_request hooks is important for backend web developers to control access and prepare requests in Flask applications.

1

Create the Flask app and login status variable

Import Flask and create an app instance called app. Then create a variable called logged_in and set it to False.

Flask

from flask import Flask

# Your code here

Need a hint?

Use app = Flask(__name__) to create the app.

Set logged_in = False as a global variable.

2

Add the before_request hook to check login

Use the @app.before_request decorator to create a function called check_login. Inside it, check if logged_in is False. If so, import and use redirect and request from Flask to redirect to /login unless the current path is already /login.

Flask

from flask import Flask

app = Flask(__name__)
logged_in = False

# Your code here

Need a hint?

Use @app.before_request above the function.

Inside the function, check if not logged_in and request.path != '/login'.

Return redirect('/login') in that case.

3

Create the home page route

Create a route for / using @app.route('/'). Define a function called home that returns the string 'Welcome to the home page!'.

Flask

from flask import Flask, redirect, request

app = Flask(__name__)
logged_in = False

@app.before_request
def check_login():
    if not logged_in and request.path != '/login':
        return redirect('/login')

# Your code here

Need a hint?

Use @app.route('/') to create the home page route.

Return the welcome string from the home function.

4

Create the login page route

Create a route for /login using @app.route('/login'). Define a function called login that returns the string 'Please log in.'.

Flask

from flask import Flask, redirect, request

app = Flask(__name__)
logged_in = False

@app.before_request
def check_login():
    if not logged_in and request.path != '/login':
        return redirect('/login')

@app.route('/')
def home():
    return 'Welcome to the home page!'

# Your code here

Need a hint?

Use @app.route('/login') to create the login page route.

Return the login prompt string from the login function.