Getting Started

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Getting Started#

Flask is a Python-based web framework that emphasizes flexibility and minimalism. It provides essential components for web development while allowing developers to choose and integrate additional tools and libraries as needed, making it suitable for both small projects and large applications.

This approach makes Flask an excellent choice for developers who prefer fine-grained control over their application’s architecture and dependencies.

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Getting Started with Flask, the basic steps.

Environment Setup: Install Flask using pip:

pip install Flask

Basic Application Structure - Forthis we create a file named app.py

from flask import Flask

app = Flask(__name__)

@app.route('/')
def hello_world():
    return 'Hello, World!'

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

Running the Application

python app.py

Routing: Add more routes to your application:

@app.route('/about')
def about():
    return 'About Page'

@app.route('/user/<username>')
def show_user_profile(username):
    return f'User {username}'

HTTP Methods: Specify HTTP methods for routes

from flask import request

@app.route('/login', methods=['GET', 'POST'])
def login():
    if request.method == 'POST':
        return 'Logging in...'
    else:
        return 'Login page'

Templates: Create a templates folder and add an HTML file, e.g., index.html:

<!DOCTYPE html>
<html>
<body>
    <h1>{{ message }}</h1>
</body>
</html>

Render the template

from flask import render_template

@app.route('/template')
def template_example():
    return render_template('index.html', message='Hello from template!')

Static Files: Create a static folder for CSS, JavaScript, and images. Reference in HTML:

<link rel="stylesheet" href="{{ url_for('static', filename='style.css') }}">

Request Data: Access form data or URL parameters

@app.route('/submit', methods=['POST'])
def submit():
    data = request.form['input_name']
    return f'Received: {data}'

Redirects and Errors

from flask import redirect, url_for, abort

@app.route('/redirect')
def redirect_example():
    return redirect(url_for('hello_world'))

@app.route('/error')
def error_example():
    abort(404)

@app.errorhandler(404)
def page_not_found(error):
    return 'Page not found', 404

Sessions

from flask import session

app.secret_key = 'your_secret_key'

@app.route('/session')
def session_example():
    if 'visits' in session:
        session['visits'] = session.get('visits') + 1
    else:
        session['visits'] = 1
    return f'Visits: {session.get("visits")}'

Database Integration (example with SQLite)

import sqlite3
from flask import g

DATABASE = 'database.db'

def get_db():
    db = getattr(g, '_database', None)
    if db is None:
        db = g._database = sqlite3.connect(DATABASE)
    return db

@app.teardown_appcontext
def close_connection(exception):
    db = getattr(g, '_database', None)
    if db is not None:
        db.close()

@app.route('/db')
def db_example():
    cur = get_db().cursor()
    cur.execute("SELECT * FROM users")
    results = cur.fetchall()
    return str(results)

Configuration

app.config['DEBUG'] = True
app.config['DATABASE_URI'] = 'sqlite:///example.db'

Extensions: Install and use Flask extensions for additional functionality, e.g., Flask-SQLAlchemy for ORM:

pip install Flask-SQLAlchemy

And the updated code that uses the Flask-SQLAlchemy library.

from flask_sqlalchemy import SQLAlchemy

app.config['SQLALCHEMY_DATABASE_URI'] = 'sqlite:///example.db'
db = SQLAlchemy(app)

class User(db.Model):
    id = db.Column(db.Integer, primary_key=True)
    username = db.Column(db.String(80), unique=True, nullable=False)

This guide covers the fundamental aspects of Flask. As you progress, explore more advanced topics like blueprints for larger applications, Flask-RESTful for API development, and Flask-WTF for form handling.

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