Flask is a lightweight, flexible web framework for building web applications in Python. It follows the WSGI (Web Server Gateway Interface) standard and is often referred to as a microframework because it provides the basic tools to build a web app but leaves most decisions (like database, authentication, etc.) to the developer.
Flask is designed to be simple, unopinionated, and extensible, making it popular for small projects, APIs, and also large applications when combined with additional libraries.
Core Concepts
Routing
Defines how URLs are mapped to Python functions (called views or endpoints). Example:
from flask import Flask
app = Flask(__name__)
@app.route('/')
def home():
return "Hello, World!"Request and Response
Flask provides an easy way to access request data and build responses. Example:
from flask import request
@app.route('/greet', methods=['POST'])
def greet():
name = request.form.get('name')
return f"Hello, {name}"Templates
Uses Jinja2 templating engine to render dynamic HTML. Example:
from flask import render_template
@app.route('/profile')
def profile():
return render_template('profile.html', name="Alice")Extensions
Flask has a rich ecosystem of extensions to add features like:
- Database ORM:
Flask-SQLAlchemy - Form validation:
Flask-WTF - Authentication:
Flask-Login - API building:
Flask-RESTful,Flask-Smorest
Key Features
- Minimalistic Core: You get routing, request/response handling, and templating out of the box.
- Flexible Structure: No imposed way to organize code.
- Extensible: Add features only if and when needed.
- Built-in Development Server and Debugger: Useful for fast iteration.
- Integrated Unit Testing Support: Comes with testing tools for writing tests easily.
When to Use Flask
- You need quick prototypes or small to medium web applications.
- You want full control over components and architecture.
- You are building REST APIs or microservices.
- You prefer adding only what you need instead of having everything pre-integrated.