Handling Forms with webapp2

If we want users to be able to post their own greetings, we need a way to process information submitted by the user with a web form. The webapp2 framework makes processing form data easy.

From Hello World to Guestbook

In order to prepare the Hello World app we've created thus far, please make the following changes:

• Rename the top level helloworld directory to guestbook
• Rename helloworld.py to guestbook.py
• Replace the handlers section of app.yaml with:

Restart the development server using the new guestbook directory.

Handling Web Forms With webapp2

Declare that you are using webapp2 by adding this libraries section to your app.yaml:

Replace the contents of guestbook/guestbook.py with the following:

Reload the page to see the form, then try submitting a message.

This version has two handlers: MainPage, mapped to the URL /, displays a web form. Guestbook, mapped to the URL /sign, displays the data submitted by the web form.

The Guestbook handler has a post() method instead of a get() method. This is because the form displayed by MainPage uses the HTTP POST method (method="post") to submit the form data. If for some reason you need a single handler to handle both GET and POST actions to the same URL, you can define a method for each action in the same class.

The code for the post() method gets the form data from self.request. Before displaying it back to the user, it uses cgi.escape() to escape HTML special characters to their character entity equivalents. cgi is a module in the standard Python library; see the documentation for cgi for more information.

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