Flask Web Development, 2nd Edition

Chapter 4. Web Forms

The templates that you worked with in Chapter 3 are unidirectional, in the sense that they allow information to flow from the server to the user. For most applications, however, there is also a need to have information that flows in the other direction, with the user providing data that the server accepts and processes.

With HTML, it is possible to create web forms, in which users can enter information. The form data is then submitted by the web browser to the server, typically in the form of a POST request. The Flask request object, introduced in Chapter 2, exposes all the information sent by the client in a request and, in particular for POST requests containing form data, provides access to the user information through request.form.

Although the support provided in Flask’s request object is sufficient for the handling of web forms, there are a number of tasks that can become tedious and repetitive. Two good examples are the generation of HTML code for the forms and the validation of the submitted form data.

The Flask-WTF extension makes working with web forms a much more pleasant experience. This extension is a Flask integration wrapper around the framework-agnostic WTForms package.

Flask-WTF and its dependencies can be installed with pip:

(venv) $ pip install flask-wtf

Configuration

Unlike most other extensions, Flask-WTF does not need to be initialized at the application level, but it expects the application to have a secret key configured. A secret ...