Using Google App Engine

Chapter 3. Python

Although HTML and CSS tell the browser how to display a page, the real power of your application will come when the HTML is dynamically generated by your Google App Engine application. Building HTML using a program is how a website shows dynamic information, such as a list of items pulled from a catalog database. Then the website allows you to pick an item and place it in your shopping cart and then a few screens later, it takes your credit card number and sells you the items. All of this requires programming. We write our instructions on how to handle incoming requests in a programming language called Python.

You will need to write a program that receives the incoming requests from the browsers and handles the request by reading and/or writing some data and then sending the next page of output back to the browser. In the next chapter, we will talk about the HyperText Transport Protocol (HTTP) and the request/response cycle in more detail. In this chapter, you get a quick introduction to the Python programming language as used in Google App Engine.

What Is Programming?

When a request comes from a browser into your web application, you must respond with a response. Let’s imagine for a moment that somehow all the requests were routed to you personally and you had to produce a response by hand for each request. It would be very similar to how telephone operators made manual phone connections in the early 1900s.

If you had to respond by hand to every request from a browser, ...