Login form and verification in Flask - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to import the Flask class.

Flask

from flask import [1]

Drag options to blanks, or click blank then click option'

ARequest

Brender_template

CFlask

Dredirect

Attempts:

3 left

💡 Hint

Common Mistakes

Importing 'Request' instead of 'Flask'.

Using lowercase 'flask' instead of 'Flask'.

The Flask class is imported from the flask module to create the app.

2fill in blank

medium

Complete the code to create a Flask app instance.

Flask

app = [1](__name__)

Drag options to blanks, or click blank then click option'

AFlask

Brender_template

Crequest

Dredirect

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'request' instead of 'Flask'.

Forgetting to pass __name__ as argument.

We create the Flask app by calling Flask with the current module name.

3fill in blank

hard

Fix the error in the route decorator to handle POST requests.

Flask

@app.route('/login', methods=[[1]])

Drag options to blanks, or click blank then click option'

A'PUT'

B'POST'

C'GET'

D'DELETE'

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'GET' which is for fetching data, not submitting.

Using 'PUT' or 'DELETE' which are not typical for forms.

The login form should accept POST requests to submit data securely.

4fill in blank

hard

Fill both blanks to get the username from the form and check if it matches 'admin'.

Flask

username = request.form.get([1])
if username == [2]:

Drag options to blanks, or click blank then click option'

A'username'

B'password'

C'admin'

D'user'

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'password' instead of 'username' to get the form data.

Comparing username to 'user' instead of 'admin'.

We get the 'username' field from the form and compare it to the string 'admin'.

5fill in blank

hard

Fill all three blanks to return a welcome message with the username if login is successful.

Flask

if username == 'admin' and password == 'secret':
    return f"Welcome, [1]!"
else:
    return [2]('login.html', [3]=True)

Drag options to blanks, or click blank then click option'

Ausername

Brender_template

Cerror

Dredirect

Attempts:

3 left

💡 Hint

Common Mistakes

Using redirect instead of render_template for failed login.

Not passing the error flag to the template.

We show a welcome message with the username, and if login fails, render the login page with an error flag.

Practice

1. What is the main purpose of a login form in a Flask web application?

easy

A. To create database tables

B. To display images on the webpage

C. To collect username and password from users

D. To send emails automatically

Solution

1. Step 1: Understand the role of a login form

   A login form is designed to collect user credentials like username and password.

2. Step 2: Identify the correct purpose in Flask context

   In Flask, the login form collects these details to verify user identity before granting access.

3. Final Answer:

   To collect username and password from users -> Option C

4. Quick Check:

   Login form = collect credentials [OK]

Hint: Login forms always gather user credentials [OK]

Common Mistakes:

• Confusing login form with other features like email or images
• Thinking login form creates database tables
• Assuming login form sends emails automatically

2. Which Flask code snippet correctly defines a route to display a login form using GET method?

easy

A. app.route('/login', methods=['GET'])\ndef login():\n return render_template('login.html')

B. app.route('/login', methods=['POST'])\ndef login():\n return render_template('login.html')

C. app.route('/login')\ndef login():\n return redirect('/home')

D. app.route('/login', methods=['DELETE'])\ndef login():\n return 'Delete method not allowed'

Solution

1. Step 1: Identify the correct HTTP method for showing a form

   Login forms are usually shown with GET requests, so methods=['GET'] is correct.

2. Step 2: Check the route and function return

   The route '/login' with methods=['GET'] returns the login.html template to display the form.

3. Final Answer:

   app.route('/login', methods=['GET'])\ndef login():\n return render_template('login.html') -> Option A

4. Quick Check:

   Show form = GET method [OK]

Hint: Use GET method to display forms in Flask routes [OK]

Common Mistakes:

• Using POST method to show the form instead of GET
• Not specifying methods list defaults to GET but unclear
• Using DELETE method which is invalid for forms

3. Given this Flask login verification code snippet, what will be the output if username='admin' and password='1234' are submitted?

from flask import Flask, request, render_template_string
app = Flask(__name__)

@app.route('/login', methods=['POST'])
def login():
    user = request.form.get('username')
    pwd = request.form.get('password')
    if user == 'admin' and pwd == '1234':
        return 'Login successful'
    else:
        return 'Login failed'

medium

A. Login successful

B. Login failed

C. SyntaxError

D. No output

Solution

1. Step 1: Check the submitted username and password

   The code compares user to 'admin' and pwd to '1234'. Both match the submitted values.

2. Step 2: Determine the returned response

   Since both match, the function returns 'Login successful'.

3. Final Answer:

   Login successful -> Option A

4. Quick Check:

   Correct credentials = Login successful [OK]

Hint: Match input values exactly to get success message [OK]

Common Mistakes:

• Confusing POST and GET methods for form data
• Assuming wrong output when credentials match
• Ignoring case sensitivity in username/password

4. Identify the error in this Flask login route code:

@app.route('/login', methods=['POST'])
def login():
    username = request.form['username']
    password = request.form['password']
    if username = 'user' and password = 'pass':
        return 'Welcome!'
    else:
        return 'Invalid credentials'

medium

A. No return statement in the function

B. Missing 'methods' argument in @app.route decorator

C. Incorrect use of request.args instead of request.form

D. Using '=' instead of '==' in the if condition

Solution

1. Step 1: Check the if condition syntax

   The code uses single '=' which is assignment, not comparison. It should be '==' to compare values.

2. Step 2: Verify other parts of the code

   The methods argument is present, request.form is correctly used, and return statements exist.

3. Final Answer:

   Using '=' instead of '==' in the if condition -> Option D

4. Quick Check:

   Comparison needs '==' not '=' [OK]

Hint: Use '==' for comparisons, '=' is assignment [OK]

Common Mistakes:

• Using '=' instead of '==' in conditions
• Forgetting to specify POST method in route
• Using request.args for POST form data

5. You want to create a Flask login system that locks out a user after 3 failed attempts. Which approach correctly combines login verification and attempt tracking?

hard

A. Use a global variable to count attempts and reset on successful login

B. Store attempt count in session and check before verifying credentials

C. Check attempts only after successful login to reset count

D. Ignore attempt count and always allow login attempts

Solution

1. Step 1: Understand where to store attempt count

   Using session storage per user is best to track attempts individually without global conflicts.

2. Step 2: Implement logic to check attempts before verifying credentials

   Check if attempts exceed 3 before allowing login verification to prevent further tries.

3. Step 3: Reset attempt count on successful login

   Resetting attempts after success avoids locking out valid users.

4. Final Answer:

   Store attempt count in session and check before verifying credentials -> Option B

5. Quick Check:

   Session tracks attempts per user [OK]

Hint: Use session to track attempts and block after limit [OK]

Common Mistakes:

• Using global variables causing shared count for all users
• Resetting attempts only after success but not checking before login
• Ignoring attempt limits and allowing unlimited tries