After_request hooks in Flask - Mini Project: Build & Apply

Using After_request Hooks in Flask

📖 Scenario: You are building a simple Flask web app that returns a greeting message. You want to add a feature that modifies the response before it is sent to the user, such as adding a custom header.

🎯 Goal: Create a Flask app with a route that returns a greeting. Then use an after_request hook to add a custom header X-Custom-Header with the value FlaskProject to every response.

📋 What You'll Learn

Create a Flask app instance named app

Define a route /hello that returns the text Hello, Flask!

Create an after_request function named add_custom_header

In add_custom_header, add the header X-Custom-Header with value FlaskProject to the response

Return the modified response from add_custom_header

💡 Why This Matters

🌍 Real World

After_request hooks are useful to add headers like security policies, CORS, or custom metadata to all responses in a web app.

💼 Career

Understanding Flask hooks is important for backend web development roles that use Python and Flask to build APIs and web services.

1

Create the Flask app and a simple route

Import Flask from flask. Create a Flask app instance called app. Define a route /hello that returns the string 'Hello, Flask!'.

Flask

# Import Flask and create app
# Define route /hello that returns 'Hello, Flask!'
# Your code here

Need a hint?

Use Flask(__name__) to create the app. Use @app.route('/hello') to define the route.

2

Create the after_request hook function

Define a function called add_custom_header that takes a parameter response. This function will be used as an after_request hook.

Flask

from flask import Flask

app = Flask(__name__)

@app.route('/hello')
def hello():
    return 'Hello, Flask!'

# Define after_request function add_custom_header with parameter response
# Your code here

Need a hint?

Define a function with one parameter named response and return it.

3

Add the custom header inside the after_request function

Inside the add_custom_header function, add a header X-Custom-Header with the value FlaskProject to the response.headers. Then return the modified response.

Flask

from flask import Flask

app = Flask(__name__)

@app.route('/hello')
def hello():
    return 'Hello, Flask!'

def add_custom_header(response):
    # Add header X-Custom-Header with value FlaskProject
    # Your code here

Need a hint?

Use response.headers['X-Custom-Header'] = 'FlaskProject' to add the header.

4

Register the after_request hook with the Flask app

Register the add_custom_header function as an after_request hook on the app by using the @app.after_request decorator above the function definition.

Flask

from flask import Flask

app = Flask(__name__)

@app.route('/hello')
def hello():
    return 'Hello, Flask!'

# Register add_custom_header as after_request hook
# Your code here
def add_custom_header(response):
    response.headers['X-Custom-Header'] = 'FlaskProject'
    return response

Need a hint?

Use @app.after_request decorator above the function add_custom_header.