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# Flask Cheatsheet

## Unique Features

- Lightweight web framework
- Jinja2 template engine
- Werkzeug WSGI toolkit
- URL routing
- Flask extensions

## Routing

Define a route

@app.route('/url')

def function_name():

# Route body

return render_template('template.html')

## Templates

<!-- Jinja2 syntax -->

{% for item in items %}

{{ item.attribute }}

{% endfor %}

## Forms

<!-- HTML syntax for form -->

<form method="POST" action="/url">

<input type="text" name="field_name">

<button type="submit">Submit</button>

</form>

<!-- Handle form submission in view function -->

@app.route('/url', methods=['GET', 'POST'])

def function_name():

if request.method == 'POST':

field_name = request.form['field_name']

# Form handling code

return redirect('/success')

return render_template('template.html')

## Database

Connect to a database

app.config['SQLALCHEMY_DATABASE_URI'] = 'sqlite:///database.db'

db = SQLAlchemy(app)

Define a model

class ModelName(db.Model):

id = db.Column(db.Integer, primary_key=True)

field_name = db.Column(db.String(255), nullable=False)

Create a migration

flask db init

flask db migrate

flask db upgrade

## Authentication

User registration

@app.route('/register', methods=['GET', 'POST'])

def register():

form = RegistrationForm()

if form.validate_on_submit():

user = User(username=form.username.data, email=form.email.data)

user.set_password(form.password.data)

db.session.add(user)

db.session.commit()

flash('Congratulations, you are now a registered user!')

return redirect(url_for('login'))

return render_template('register.html', title='Register', form=form)

User login

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

def login():

form = LoginForm()

if form.validate_on_submit():

user = User.query.filter_by(username=form.username.data).first()

if user is None or not user.check_password(form.password.data):

flash('Invalid username or password')

return redirect(url_for('login'))

login_user(user, remember=form.remember_me.data)

return redirect(url_for('index'))

return render_template('login.html', title='Sign In', form=form)

User logout

@app.route('/logout')

def logout():

logout_user()

return redirect(url_for('index'))

## Resources

- [Flask Documentation](https://flask.palletsprojects.com/)
- [Flask Mega-Tutorial](https://blog.miguelgrinberg.com/post/the-flask-mega-tutorial-part-i-hello-world)
- [Flask Extensions](https://flask.palletsprojects.com/en/2.0.x/extensions/)