User model with password in Flask - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the purpose of hashing passwords in a User model?

Hashing passwords protects user data by converting the password into a secure, unreadable format. This way, even if the database is compromised, the actual passwords are not exposed.

beginner

Which Flask extension is commonly used to hash passwords securely?

Flask-Bcrypt is commonly used to hash passwords securely in Flask applications. It provides easy-to-use methods to hash and check passwords.

beginner

In a Flask User model, why should you never store the password as plain text?

Storing passwords as plain text is risky because if the database is leaked, attackers get direct access to user passwords. Hashing prevents this by storing only the hashed version.

intermediate

What is the typical method name used in a Flask User model to set a password securely?

A typical method is called set_password. It takes the plain password, hashes it, and stores the hashed password in the model.

intermediate

How do you verify a user's password during login in a Flask app?

You use a method like check_password that compares the hashed password stored in the database with the hash of the password entered by the user. If they match, the password is correct.

Which of these is the safest way to store user passwords in Flask?

A Hash passwords using Flask-Bcrypt

B Store passwords as plain text

C Encrypt passwords with reversible encryption

D Store passwords in cookies

Hashing passwords with Flask-Bcrypt is the safest because it is one-way and secure. Plain text and reversible encryption are unsafe.

What does the set_password method usually do in a Flask User model?

A Hashes the password and stores it

B Stores the password as plain text

C Deletes the password

D Sends the password by email

set_password hashes the password before storing it to keep it secure.

Which Flask extension helps with password hashing?

A Flask-Login

B Flask-Mail

C Flask-Bcrypt

D Flask-WTF

Flask-Bcrypt provides secure password hashing functions.

Why should passwords never be stored in plain text?

A It makes the database slower

B It risks exposing user passwords if leaked

C It wastes storage space

D It is required by Flask

Storing passwords in plain text risks exposing them if the database is compromised.

How do you check if a password entered by a user matches the stored password?

A Compare plain text passwords directly

B Use a random number generator

C Send password to admin for verification

D Hash the entered password and compare with stored hash

You hash the entered password and compare it to the stored hashed password to verify.

Explain how to create a User model in Flask that securely handles passwords.

Think about how to protect user passwords from being stolen.

Describe the steps to verify a user's password during login in a Flask app.

Focus on how to safely check passwords without revealing them.

Practice

1. What is the main purpose of the set_password method in a Flask user model?

easy

A. To delete the user's password from the database

B. To hash and store the user's password securely

C. To check if the password entered matches the stored password

D. To display the user's password in plain text

Solution

1. Step 1: Understand the role of set_password

   This method is used to convert a plain password into a secure hashed version before saving it.

2. Step 2: Differentiate from check_password

   check_password is for verifying passwords, not setting them.

3. Final Answer:

   To hash and store the user's password securely -> Option B

4. Quick Check:

   set_password hashes password [OK]

Hint: Remember: set_password hashes, check_password verifies [OK]

Common Mistakes:

• Confusing set_password with check_password
• Thinking set_password shows the password
• Assuming set_password deletes passwords

2. Which of the following is the correct way to define a password hashing method in a Flask user model using Werkzeug?

easy

A. def set_password(self, password): return check_password_hash(self.password_hash, password)

B. def set_password(self, password): self.password = password

C. def set_password(self, password): self.password_hash = password

D. def set_password(self, password): self.password_hash = generate_password_hash(password)

Solution

1. Step 1: Identify correct hashing usage

   The method must use generate_password_hash to hash the password before storing.

2. Step 2: Check assignment to password_hash

   The hashed password should be saved in self.password_hash, not plain password.

3. Final Answer:

   def set_password(self, password): self.password_hash = generate_password_hash(password) -> Option D

4. Quick Check:

   Use generate_password_hash to store hashed password [OK]

Hint: Use generate_password_hash to hash passwords [OK]

Common Mistakes:

• Storing plain password instead of hashed
• Using check_password_hash inside set_password
• Assigning password to wrong attribute

3. Given this Flask user model snippet, what will user.check_password('secret') return if the password was set with user.set_password('secret')?

from werkzeug.security import generate_password_hash, check_password_hash

class User:
    def __init__(self):
        self.password_hash = ''
    def set_password(self, password):
        self.password_hash = generate_password_hash(password)
    def check_password(self, password):
        return check_password_hash(self.password_hash, password)

user = User()
user.set_password('secret')

medium

A. None

B. False

C. True

D. Raises an error

Solution

1. Step 1: Understand password setting

   The password 'secret' is hashed and stored in password_hash.

2. Step 2: Check password verification

   check_password compares the hash with 'secret' and returns True if they match.

3. Final Answer:

   True -> Option C

4. Quick Check:

   Matching password returns True [OK]

Hint: check_password returns True if password matches hash [OK]

Common Mistakes:

• Expecting False for correct password
• Thinking check_password returns the hash
• Assuming error if password matches

4. Identify the error in this Flask user model code snippet:

from werkzeug.security import generate_password_hash, check_password_hash

class User:
    def __init__(self):
        self.password_hash = None
    def set_password(self, password):
        self.password_hash = generate_password_hash(password)
    def check_password(self, password):
        return check_password_hash(password, self.password_hash)

medium

A. The order of arguments in check_password_hash is reversed

B. password_hash should be initialized as an empty string, not None

C. set_password should return the hashed password

D. The class is missing a username attribute

Solution

1. Step 1: Review check_password_hash usage

   The correct order is check_password_hash(stored_hash, password).

2. Step 2: Identify argument mistake

   The code passes password first and self.password_hash second, which is wrong.

3. Final Answer:

   The order of arguments in check_password_hash is reversed -> Option A

4. Quick Check:

   check_password_hash needs (hash, password) order [OK]

Hint: check_password_hash(hash, password) order matters [OK]

Common Mistakes:

• Swapping arguments in check_password_hash
• Initializing password_hash as None causes no error but is not best
• Expecting set_password to return a value
• Confusing missing attributes with password errors

5. You want to add a method change_password to your Flask user model that updates the password only if the old password matches. Which implementation correctly applies this logic?

hard

A. def change_password(self, old_password, new_password):
if self.check_password(old_password):
self.set_password(new_password)
return True
return False

B. def change_password(self, old_password, new_password):
self.set_password(new_password)
return True

C. def change_password(self, old_password, new_password):
if old_password == new_password:
self.set_password(new_password)
return True
return False

D. def change_password(self, old_password, new_password):
if not self.check_password(new_password):
self.set_password(old_password)
return True
return False

Solution

1. Step 1: Verify old password before changing

   The method must check if the old password matches using check_password.

2. Step 2: Update password only if old password is correct

   If the check passes, call set_password with the new password and return True; else return False.

3. Final Answer:

   def change_password(self, old_password, new_password): if self.check_password(old_password): self.set_password(new_password) return True return False -> Option A

4. Quick Check:

   Change password only if old password matches [OK]

Hint: Always verify old password before setting new one [OK]

Common Mistakes:

• Changing password without verifying old password
• Comparing old and new passwords incorrectly
• Swapping old and new passwords in checks