How to Install Flask-Login in Python

Flask-Login is a popular extension for Flask. It simplifies user authentication. This guide will help you install it easily.

Prerequisites

Before installing Flask-Login, ensure you have Python installed. You also need Flask. If not, install Flask first.

pip install flask

Check your Python version. Flask-Login works with Python 3.6+. Verify with:

python --version

Install Flask-Login

Use pip to install Flask-Login. Run this command in your terminal:

pip install flask-login

This will download and install Flask-Login. It also installs dependencies automatically.

Verify Installation

Check if Flask-Login installed correctly. Open Python shell and import it:

 
import flask_login
print(flask_login.__version__)

If no errors appear, installation was successful. You should see the version number.

Basic Flask-Login Setup

Now, let's set up a basic Flask app with Flask-Login. First, create a new Python file.

 
from flask import Flask
from flask_login import LoginManager

app = Flask(__name__)
app.secret_key = 'your_secret_key'

login_manager = LoginManager()
login_manager.init_app(app)

if __name__ == '__main__':
    app.run()

This code initializes Flask-Login. The secret_key is essential for session security.

User Model Setup

Flask-Login requires a user model. Create a simple user class with required methods.

 
from flask_login import UserMixin

class User(UserMixin):
    def __init__(self, id):
        self.id = id

The UserMixin provides default implementations for required methods.

User Loader Function

Flask-Login needs a user loader. This function loads a user by their ID.

 
@login_manager.user_loader
def load_user(user_id):
    return User(user_id)

This callback is used to reload the user object from the user ID.

Login and Logout Routes

Now, add login and logout routes to your Flask app.

 
from flask import redirect, url_for
from flask_login import login_user, logout_user

@app.route('/login')
def login():
    user = User(1)
    login_user(user)
    return redirect(url_for('protected'))

@app.route('/logout')
def logout():
    logout_user()
    return 'Logged out'

The login_user and logout_user functions handle authentication.

Protected Route

Create a protected route that requires authentication.

 
from flask_login import login_required

@app.route('/protected')
@login_required
def protected():
    return 'Protected page'

The login_required decorator ensures only logged-in users can access this route.

Testing the Application

Run your Flask application and test the routes.

flask run

Visit /login first, then try accessing /protected. You should see the protected content.

Common Issues

If you get errors, check these common issues:

1. Missing secret_key in Flask app

2. Forgot to initialize LoginManager

3. User model doesn't implement required methods

Conclusion

Flask-Login makes user authentication simple in Flask. Now you can secure your web applications easily.

For more Python packages, check our guides on Install Babel for Python Internationalization or How to Install pytz in Python Easily.