Now that we know about the two modes of request handling in Google App Engine, how they work, and their respective pros and cons, it's time to divert our attention to request handlingfrom another aspect. As we discussed in the previous chapter, app.yaml is a manifest of your application, and it defines what your application really is. One of the major things that it defines is how your application processes URLs. There are three things that app.yaml defines:

To define which URLs are processed, you can define absolute URLs that start with the / character. Alternatively, if you want some flexibility, you can use regular expressions. Regular expressions might contain regular expression groups, which can later be used in a handler description to specify the URL patterns. We will see this in an example shortly.

The...

We have been returning plain strings so far, and that's been handy for a while. However, things get pretty complicated if you have to return more information with a more detailed and structured page to the user. This is where this string approach gets very complicated and hard to manage.

That's where templates come into play. Just to recap, the idea of a template is to have some placeholder within the content, where the actual values will be rendered so that you can pass to them. There are many templating libraries (each have their different syntax as well at times), but one of the most widely used one is the templating language, which is used by Django, the popular web framework. It is quit intuitive and easy to understand. There's another third-party library named jinja2 that adopts the Django template language in the form of a separate library. Google App Engine has both the Django templates and jinja2 available. If you want to use some other templating...

We are making progress. From strings to templates, but still no cosmetics. Just plain HTML is what we are serving. However, to add some beautification to the pages, we will have to style it. To style the pages better, we will need style sheets, and style sheets might need images to beautify our pages This means that we have to serve static files as well.

Serving static files is pretty simple. You just need to add a handler in your app.yaml file as usual, but instead of the script node, you need to add a static_dir node, which indicates the directory in which the files that you want to serve are present. Let's modify our earlier app to serve some static files such as style sheets and images:

- handlers:
  - url:/assets/.*
    static_dir: assets

You may have already guessed that any URL that starts with /assets will be handled by this handler. However, instead of invoking a script, it maps itself to a directory called assets, which is located at the root of your...

Until now, we have been writing either plain CGI programs, or WSGI handlers that we map in our application manifest file by using regular expressions. This approach of course works, but it is not scalable for even small projects with few pages to be served. This is where we need to grow beyond this and use web frameworks. We have a lot of variety in Python web frameworks, and everyone has their own favorite list of frameworks. App Engine has built-in frameworks that are a part of the App Engine libraries that are available within the runtime environment. However, these might not be the frameworks that you prefer to work with. You might want to use your own favorite web frameworks. Fortunately, that's possible and easy too. We shall review both using built-in frameworks or rolling in your own favorite in the following sections.