# Flask Cheatsheet
## Unique Features
- Lightweight web framework
- Jinja2 template engine
- Werkzeug WSGI toolkit
- URL routing
- Flask extensions
## Routing
```python
# Define a route
@app.route('/url')
def function_name():
# Route body
return render_template('template.html')
```
## Templates
```html
<!-- Jinja2 syntax -->
{% for item in items %}
{{ item.attribute }}
{% endfor %}
```
## Forms
```html
<!-- 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
```python
# 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
```python
# 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/)