Create a Python web application that retrieves and displays weather information for major cities using Flask. Learn to set up a virtual environment, install necessary packages, handle environment variables, and structure your project with static files and templates. Develop a weather module to interact with the OpenWeatherMap API, implement Flask routing, and create a user-friendly interface. Explore how to switch to a production server, handle unexpected user input, and ultimately deploy your application to the web. This comprehensive tutorial covers everything from project setup to deployment, making it ideal for Python beginners looking to build their first web application.