Securely Load Environment Variables in Python with Flask-DotEnv

import os
from flask import Flask
from dotenv import load_dotenv

# Load environment variables from a .env file (if it exists)
# This should be called early in your application lifecycle
load_dotenv()

app = Flask(__name__)

# Accessing sensitive configuration from environment variables
# This keeps secrets out of your codebase and version control
SECRET_KEY = os.getenv("FLASK_SECRET_KEY")
DATABASE_URL = os.getenv("DATABASE_URL")
API_KEY = os.getenv("THIRD_PARTY_API_KEY")

if not SECRET_KEY:
    print("WARNING: FLASK_SECRET_KEY not set! Using a default (INSECURE FOR PRODUCTION).")
    SECRET_KEY = "super_secret_dev_key" # DO NOT USE IN PRODUCTION

# Example route using a secret
@app.route('/')
def index():
    return f"Welcome! Your API Key (first 5 chars): {API_KEY[:5]}..."

@app.route('/secret')
def secret_data():
    if SECRET_KEY == "super_secret_dev_key":
        return "Developer mode - real secret key not set!"
    return f"Secret key in use: {SECRET_KEY[:10]}..."

if __name__ == '__main__':
    # Create a dummy .env file for testing if it doesn't exist
    if not os.path.exists('.env'):
        with open('.env', 'w') as f:
            f.write("FLASK_SECRET_KEY=my_secure_flask_secret_key_12345
")
            f.write("DATABASE_URL=postgresql://user:pass@host:port/db
")
            f.write("THIRD_PARTY_API_KEY=my_very_secure_api_key_for_external_service
")
        print("Created a dummy .env file for demonstration.")
        print("Please restart the script or manually load .env variables.")

    app.run(debug=True)