1. Flask - Home
Flask is a lightweight web framework for Python that enables rapid development of web applications. It is designed to be simple, flexible, and extensible. In this section, we'll explore the basic components of Flask and how to set up your first application.
app = Flask(__name__)
@app.route('/')
def home():
return 'Welcome to Flask Home!'
if __name__ == '__main__':
app.run(debug=True)
2. Flask - Overview
Flask provides a simple, yet powerful way to build web applications. It allows developers to add only the components they need while leaving out unnecessary features, making it a great option for small to medium-sized projects.
app = Flask(__name__)
@app.route('/')
def overview():
return 'Flask Overview'
3. Flask - Environment
Setting up a proper environment is crucial for running Flask applications. It's recommended to use virtual environments to avoid conflicts between package dependencies.
# Activate the environment (on Windows) flaskenv\Scripts\activate
4. Flask - Application
Flask applications are created by instantiating the Flask class. Each Flask application is represented by an instance of the Flask class.
app = Flask(__name__)
@app.route('/')
def application():
return 'Flask Application'
5. Flask - Routing
Routing in Flask allows the developer to map URLs to functions. When a user visits a specific URL, Flask triggers the corresponding function.
def about():
return 'About Page'
6. Flask - Variable Rules
Flask allows the use of variables in URLs. This means you can capture dynamic parts of the URL and pass them to your functions.
def user_profile(username):
return f'User Profile: {username}'
7. Flask - URL Building
URL Building is an essential Flask feature that allows you to generate URLs dynamically, avoiding hard-coded paths in your code.
@app.route('/next')
def next_page():
return url_for('user_profile', username='john')
8. Flask - HTTP Methods
Flask supports different HTTP methods such as GET, POST, PUT, DELETE, etc. These methods are used to handle different types of requests from the client.
def submit():
return 'Form Submitted'
9. Flask - Templates
Flask uses Jinja2 templates to render dynamic content. This allows you to separate HTML structure from Python code, making the application more maintainable.
@app.route('/home')
def home_page():
return render_template('home.html')
10. Flask - Static Files
Flask provides a way to serve static files (like images, CSS, and JavaScript) to clients. Static files are placed in a special folder named static.
def static_files(filename):
return send_from_directory('static', filename)
11. Flask - Request Object
The Flask Request object allows you to access data sent by the client in HTTP requests. It provides methods to handle data sent via GET, POST, and other HTTP methods.
@app.route('/submit', methods=['POST'])
def submit():
username = request.form['username']
return f'Hello {username}'
12. Sending Form Data to Template
Flask allows you to send form data to templates for rendering dynamic content. This is useful for showing messages or passing values between views and templates.
@app.route('/form', methods=['GET', 'POST'])
def form():
if request.method == 'POST':
username = request.form['username']
return render_template('result.html', username=username)
return render_template('form.html')
14. Flask - Sessions
Sessions in Flask allow you to store data across requests for a specific user. Unlike cookies, session data is stored on the server-side but can be accessed by the client via a session ID stored in a cookie.
@app.route('/setsession')
def set_session():
session['username'] = 'john'
return 'Session Set'
15. Flask - Redirect & Error
Flask provides a way to redirect users to different routes and handle errors gracefully. You can use the redirect() function to navigate to another URL and handle errors using custom error pages.
@app.route('/redirect')
def redirect_to():
return redirect(url_for('home'))
@app.errorhandler(404)
def page_not_found(error):
return 'Page not found', 404
16. Flask - Message Flashing
Message flashing in Flask allows you to display temporary messages to users, usually after a form submission or other important action.
@app.route('/flashmessage')
def flash_message():
flash('Form Submitted Successfully')
return redirect(url_for('home'))
17. Flask - File Uploading
Flask supports file uploading through the use of the request.files object. You can handle user-uploaded files and save them to the server.
@app.route('/upload', methods=['POST'])
def upload_file():
if 'file' in request.files:
file = request.files['file']
file.save(f'./uploads/{file.filename}')
return 'File Uploaded'
18. Flask - Extensions
Flask has a wide range of extensions that add functionality to your application, such as database integration, form validation, and more. These extensions help enhance Flask’s capabilities.
app.config['SQLALCHEMY_DATABASE_URI'] = 'sqlite:///database.db'
db = SQLAlchemy(app)
19. Flask - Mail
Flask-Mail extension provides easy-to-use functionality for sending emails in Flask applications. It integrates seamlessly with Flask to send emails through different mail servers.
mail = Mail(app)
@app.route('/sendmail')
def send_mail():
msg = Message('Hello', recipients=['example@example.com'])
msg.body = 'This is a test email'
mail.send(msg)
return 'Mail Sent'
20. Flask - WTF
Flask-WTF is an extension that simplifies working with forms in Flask applications. It integrates Flask with WTForms, providing form validation and protection against Cross-Site Request Forgery (CSRF).
from wtforms import StringField, SubmitField
from wtforms.validators import DataRequired
class MyForm(FlaskForm):
name = StringField('Name', validators=[DataRequired()])
submit = SubmitField('Submit')
21. Flask - SQLite
Flask can be easily integrated with SQLite, a lightweight database, for simple applications. SQLite is serverless and stores data in a single file, making it ideal for small-scale applications.
import sqlite3
app = Flask(__name__)
def get_db():
if 'db' not in g:
g.db = sqlite3.connect('database.db')
return g.db
22. Flask - SQLAlchemy
Flask-SQLAlchemy is an extension for Flask that adds support for SQLAlchemy, a powerful ORM (Object Relational Mapper). This makes working with databases simpler by allowing you to work with Python objects rather than writing raw SQL queries.
app.config['SQLALCHEMY_DATABASE_URI'] = 'sqlite:///mydb.db'
db = SQLAlchemy(app)
class User(db.Model):
id = db.Column(db.Integer, primary_key=True)
name = db.Column(db.String(50), nullable=False)
23. Flask - Sijax
Flask-Sijax is an extension that allows Flask applications to communicate asynchronously with the client using AJAX. It helps in making applications more interactive by enabling real-time communication between the server and client.
app = Flask(__name__)
app.config['SIJAX_STATIC_PATH'] = 'static/'
sijax = Sijax(app)
24. Flask - Deployment
Flask applications can be deployed on various platforms such as Heroku, AWS, and more. Deployment involves setting up the web server, configuring the application, and ensuring it runs in production mode.
web: python app.py
25. Flask - FastCGI
FastCGI is a protocol for interfacing interactive programs with a web server. It helps in improving performance for web applications. Flask can be used with FastCGI for handling requests more efficiently.
pip install flup
from flup.server.fcgi import WSGIServer
from app import app
WSGIServer(app).run()
26. Flask Useful Resources
There are many useful resources for learning Flask, including official documentation, tutorials, and community forums. These resources help in understanding Flask better and improving development skills.
27. Flask - Quick Guide
Flask provides a quick guide for developers to set up their first application, covering everything from installation to deployment. A quick guide helps beginners start working with Flask efficiently.
pip install flask
# Run the app
python app.py
28. Flask - Useful Resources
Additional useful resources for Flask developers, including tools, templates, and frameworks that complement Flask for building more complex applications.
29. Flask - Discussion
Flask has a vibrant community where developers discuss best practices, troubleshooting, and new features. Participating in discussions helps improve your knowledge and keeps you updated with Flask advancements.