Agent Skills: app.py

When to use this skill

Use this skill whenever the user wants to:

• Build Python web applications with Flask routing and templates
• Configure WSGI, blueprints, extensions, and deployment
• Integrate Flask-SQLAlchemy, Flask-Login, or other extensions
• Create REST APIs or serve server-rendered pages with Jinja2

How to use this skill

Workflow

1. Create app — instantiate Flask and define routes
2. Add templates — use Jinja2 for HTML rendering
3. Organize with blueprints — split features into blueprint modules
4. Configure and deploy — set environment config, deploy with Gunicorn

Quick Start Example

# app.py
from flask import Flask, render_template, request, jsonify

app = Flask(__name__)
app.config['SECRET_KEY'] = 'change-me-in-production'

@app.route('/')
def index():
    return render_template('index.html', title='Home')

@app.route('/api/items', methods=['GET', 'POST'])
def items():
    if request.method == 'POST':
        data = request.get_json()
        # Process and save item
        return jsonify({'status': 'created', 'item': data}), 201
    return jsonify({'items': []})

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

Application Factory Pattern

# __init__.py
from flask import Flask

def create_app(config_name='default'):
    app = Flask(__name__)
    app.config.from_object(config[config_name])

    # Initialize extensions
    db.init_app(app)
    login_manager.init_app(app)

    # Register blueprints
    from .auth import auth_bp
    app.register_blueprint(auth_bp, url_prefix='/auth')

    from .main import main_bp
    app.register_blueprint(main_bp)

    return app

# Development
flask --app app run --debug

# Production
gunicorn -w 4 -b 0.0.0.0:8000 "app:create_app()"

Blueprint Example

# auth/routes.py
from flask import Blueprint, render_template, redirect, url_for

auth_bp = Blueprint('auth', __name__, template_folder='templates')

@auth_bp.route('/login', methods=['GET', 'POST'])
def login():
    if request.method == 'POST':
        # Authenticate user
        return redirect(url_for('main.index'))
    return render_template('auth/login.html')

Best Practices

• Use the application factory pattern with blueprints for modularity
• Keep sensitive configuration out of source code — use environment variables
• Deploy with Gunicorn or uWSGI behind a reverse proxy (nginx)
• Enable CSRF protection with Flask-WTF; set security headers
• Use flask shell for interactive debugging with app context

Reference

• Official documentation: https://flask.palletsprojects.com/

Keywords

flask, Python web, routing, templates, Jinja2, blueprints, WSGI, REST API, Gunicorn