User model with password in Flask - Mini Project: Build & Apply

User model with password

📖 Scenario: You are building a simple Flask app that needs to store user information securely. You want to create a user model that keeps usernames and hashed passwords.

🎯 Goal: Create a Flask user model class called User with attributes for username and password_hash. Implement a method to set the password by hashing it and a method to check a password against the stored hash.

📋 What You'll Learn

Create a User class with username and password_hash attributes

Add a method set_password(password) that hashes the password and stores it in password_hash

Add a method check_password(password) that returns True if the password matches the stored hash

Use werkzeug.security functions generate_password_hash and check_password_hash

💡 Why This Matters

🌍 Real World

Web applications need to store user passwords securely to protect user accounts and data.

💼 Career

Understanding how to hash and verify passwords is essential for backend developers working on user authentication.

1

Create the User class with username and password_hash attributes

Create a class called User with an __init__ method that takes username and sets self.username to it. Also initialize self.password_hash to None.

Flask

class User:
    def __init__(self, username):
        # Your code here

Hint

Define a class named User. Inside __init__, assign username to self.username and set self.password_hash to None.

2

Import password hashing functions

Add an import statement to import generate_password_hash and check_password_hash from werkzeug.security.

Flask

from werkzeug.security import generate_password_hash, check_password_hash

class User:
    def __init__(self, username):
        self.username = username
        self.password_hash = None
# Your code here

Hint

Use from werkzeug.security import generate_password_hash, check_password_hash to import the needed functions.

3

Add set_password method to hash and store password

Inside the User class, add a method called set_password that takes password as a parameter. Use generate_password_hash(password) to create a hash and assign it to self.password_hash.

Flask

from werkzeug.security import generate_password_hash, check_password_hash

class User:
    def __init__(self, username):
        self.username = username
        self.password_hash = None

    # Add set_password method here
    # Your code here

Hint

Define set_password method that sets self.password_hash using generate_password_hash(password).

4

Add check_password method to verify password

Inside the User class, add a method called check_password that takes password as a parameter and returns the result of check_password_hash(self.password_hash, password).

Flask

from werkzeug.security import generate_password_hash, check_password_hash

class User:
    def __init__(self, username):
        self.username = username
        self.password_hash = None

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

    # Add check_password method here
    # Your code here

Hint

Define check_password method that returns check_password_hash(self.password_hash, password).

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