Email verification pattern in Flask - Mini Project: Build & Apply

Email verification pattern

📖 Scenario: You are building a simple Flask web app where users can register with their email addresses. To ensure the email is valid, you want to implement an email verification pattern.This project guides you through setting up the data, configuration, core logic, and completion of the email verification feature.

🎯 Goal: Build a Flask app that accepts user email input, checks if the email format is valid using a regular expression, and displays a message indicating whether the email is valid or not.

📋 What You'll Learn

Create a Flask app with a route to accept email input

Use a regular expression to verify the email format

Display a success message if the email is valid

Display an error message if the email is invalid

💡 Why This Matters

🌍 Real World

Email verification is a common feature in web apps to ensure users provide valid contact information before accessing services.

💼 Career

Understanding how to implement email validation and user input handling in Flask is essential for backend web development roles.

1

DATA SETUP: Create a Flask app and import necessary modules

Write code to import Flask, request, and render_template from flask. Then create a Flask app instance called app.

Flask

from flask import Flask, request, render_template

# Create the Flask app instance
# Your code here

Hint

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

2

CONFIGURATION: Define a regular expression pattern for email validation

Create a variable called email_pattern and assign it the regular expression string r"^[\w\.-]+@[\w\.-]+\.\w+$" to match valid email formats.

Flask

from flask import Flask, request, render_template

app = Flask(__name__)

# Define the email validation regex pattern
# Your code here

Hint

The regex checks for characters before and after '@' and a domain suffix.

3

CORE LOGIC: Create a route to handle email input and validate it

Write a Flask route for '/' that accepts GET and POST methods. Inside the route function verify_email, get the email from request.form with key 'email'. Use the re module to check if the email matches email_pattern. Return render_template('result.html', message=message) where message is 'Valid email!' if it matches or 'Invalid email!' if not.

Flask

from flask import Flask, request, render_template
import re

app = Flask(__name__)

email_pattern = r"^[\w\.-]+@[\w\.-]+\.\w+$"

# Create route '/' with GET and POST methods
# Your code here

Hint

Use @app.route decorator and request.form.get('email', '') to get the email.

4

COMPLETION: Add the HTML template to display the email input form and result message

Create a simple HTML form in a file named templates/result.html that shows an input field named email and a submit button. Below the form, display the message variable passed from Flask inside a paragraph tag.

Flask

from flask import Flask, request, render_template
import re

app = Flask(__name__)

email_pattern = r"^[\w\.-]+@[\w\.-]+\.\w+$"

@app.route('/', methods=['GET', 'POST'])
def verify_email():
    message = ''
    if request.method == 'POST':
        email = request.form.get('email', '')
        if re.match(email_pattern, email):
            message = 'Valid email!'
        else:
            message = 'Invalid email!'
    return render_template('result.html', message=message)

# Create templates/result.html with form and message display
# Your code here

Hint

Use a form with method POST and display the message variable inside a paragraph.

Practice

1. What is the main purpose of email verification in a Flask application?

easy

A. To store user data securely in the database

B. To confirm that the user owns the provided email address

C. To speed up the login process

D. To encrypt the user's password

Solution

1. Step 1: Understand email verification purpose

   Email verification is used to confirm that the user actually owns the email they provided during signup.

2. Step 2: Differentiate from other security tasks

   Encrypting passwords and speeding login are different tasks unrelated to email verification.

3. Final Answer:

   To confirm that the user owns the provided email address -> Option B

4. Quick Check:

   Email verification = Confirm ownership [OK]

Hint: Email verification confirms user email ownership [OK]

Common Mistakes:

• Confusing email verification with password encryption
• Thinking it speeds up login
• Assuming it stores data securely

2. Which Flask library is commonly used to create timed tokens for email verification?

easy

A. flask_sqlalchemy

B. flask_login

C. itsdangerous

D. flask_mail

Solution

1. Step 1: Identify token generation library

   The itsdangerous library provides URLSafeTimedSerializer to create timed tokens.

2. Step 2: Differentiate from other Flask extensions

   flask_sqlalchemy manages databases, flask_login handles user sessions, and flask_mail sends emails but does not create tokens.

3. Final Answer:

   itsdangerous -> Option C

4. Quick Check:

   Token creation = itsdangerous [OK]

Hint: Use itsdangerous for timed token creation [OK]

Common Mistakes:

• Choosing flask_mail for token creation
• Confusing flask_login with token generation
• Selecting flask_sqlalchemy incorrectly

3. Given this Flask code snippet, what will verify_token(token) return if the token is expired?

from itsdangerous import URLSafeTimedSerializer, SignatureExpired

serializer = URLSafeTimedSerializer('secret-key')

def verify_token(token):
    try:
        email = serializer.loads(token, max_age=3600)
        return email
    except SignatureExpired:
        return None

medium

A. Returns None

B. Raises a SignatureExpired exception

C. The email string inside the token

D. Returns an empty string

Solution

1. Step 1: Understand token verification logic

   The function tries to load the token with a max age of 3600 seconds (1 hour).

2. Step 2: Handle expired token exception

   If the token is expired, it raises SignatureExpired, which is caught and returns None.

3. Final Answer:

   Returns None -> Option A

4. Quick Check:

   Expired token returns None [OK]

Hint: Expired tokens return None in try-except block [OK]

Common Mistakes:

• Expecting exception to propagate
• Assuming it returns empty string
• Thinking it returns the email anyway

4. Identify the error in this Flask email verification token generation code:

from itsdangerous import URLSafeTimedSerializer

serializer = URLSafeTimedSerializer('secret-key')

def generate_token(email):
    token = serializer.dumps(email)
    return token

# Later verification
email = serializer.loads(token, max_age=3600)

medium

A. Token variable is undefined at verification

B. Missing secret key in serializer initialization

C. max_age parameter is invalid in loads()

D. Using dumps() instead of loads() to verify

Solution

1. Step 1: Check token generation and usage

   The token is generated inside generate_token but not stored or passed outside.

2. Step 2: Verify token usage scope

   At verification, token is used but not defined in that scope, causing a NameError.

3. Final Answer:

   Token variable is undefined at verification -> Option A

4. Quick Check:

   Undefined token variable causes error [OK]

Hint: Ensure token variable is defined before verification [OK]

Common Mistakes:

• Ignoring variable scope for token
• Thinking secret key is missing
• Misusing max_age parameter

5. You want to implement email verification in Flask so that users receive a link with a token that expires after 24 hours. Which approach correctly combines token creation, sending email, and verification?

hard

A. Generate token without secret key, send email, verify token ignoring expiration

B. Store plain email in database, send email without token, verify by matching email only

C. Send token as plain text in email body, verify token with max_age=3600

D. Generate token with URLSafeTimedSerializer, send email with token link, verify token with max_age=86400

Solution

1. Step 1: Create token with expiration

   Use URLSafeTimedSerializer with a secret key to generate a token that expires after 86400 seconds (24 hours).

2. Step 2: Send email with token link and verify properly

   Send the token inside a URL link in the email. Verify the token using loads() with max_age=86400 to enforce expiration.

3. Final Answer:

   Generate token with URLSafeTimedSerializer, send email with token link, verify token with max_age=86400 -> Option D

4. Quick Check:

   Token creation + email + 24h expiry = Generate token with URLSafeTimedSerializer, send email with token link, verify token with max_age=86400 [OK]

Hint: Use max_age=86400 for 24h token expiry [OK]

Common Mistakes:

• Not using tokens in email links
• Ignoring token expiration
• Sending tokens without secret key