Web forms are used in web applications to accept data from a user and send it to the server for validation and processing. To generate the required forms (for example drop-downs, entry fields, and even password fields that hide their contents from the user), the Flask-WTF module and the WTForms module are used. These modules contain classes that make it possible to create the form components and to ensure that the data entered into them is valid for that field.

For our simple application, only one form is created. The ArenaForm form inherits from the FlaskFor class and contains a description attribute and field called selections. This field is a SelectField, which will create a drop-down list on the web page. It requires a description string and uses the keyword choices to generate the list of the choices available in the drop-down list. As the members of the drop-down list will be generated dynamically within the view (explained as follows), an empty list is passed to the choices keyword here:

from flask_wtf import FlaskForm
from wtforms import SelectField
class ArenaForm(FlaskForm):
    description  = "Use the dropdown to select an arena."
    selections = SelectField('Select an Arena',choices=[])

Other field classes, such as TextField, BooleanField, StringField, FloatField, PasswordField, and many others, are available from WTForms for implementation of complex web applications. Also, because they are Python objects, forms can be updated to include other data attributes on the fly, as we will see as we proceed further.