Routes

noreply@example.com (AG Sayyed) — Fri, 25 Jul 2025 00:00:00 +0000

This document details how to create and configure routes in Flask, return responses, manage configuration, and structure projects for maintainability. It covers decorators, JSON responses, environment variables, and best practices for organizing Flask code.

Introduction to Flask Routes

Routes in Flask define how URLs are handled by the application. Each route is associated with a function that returns a response to the client.

Creating a Basic Flask Application

Install Flask and create a Python file (e.g., app.py).
Import the Flask class and instantiate the app:

1from flask import Flask
2app = Flask(__name__)

Define a route using the @app.route decorator:

1@app.route('/')
2def hello_world():
3 return '<b>my first Flask application in action!</b>'

Running the Flask Application

Set environment variables for the app and environment:

1export FLASK_APP=app.py
2export FLASK_ENV=development
3flask run

The app runs on http://localhost:5000 by default.
Use --app and --debug flags for configuration and development mode.

Returning Responses and JSON

Return text or HTML directly from route functions.
To return JSON, return a serializable object (e.g., dictionary) or use jsonify:

1from flask import jsonify
2@app.route('/json')
3def json_example():
4 return jsonify(message='Hello, JSON!')

The response will have content type application/json.

Flask Configuration Options