Form Validation and Data and Error Handling with Flask-WTF
In this lesson, we will learn how to validate the data received from the form and how to handle these validation errors.
Form validation
The Flask-WTF forms provide us with some helpful functions that make the task of distinguishing between a GET or POST request easier. Let us discuss them below.
form.is_submitted()
This function is inherited from the WTForms module. It returns true if all the fields of a form have been completely filled by the user. Otherwise, it returns false. This function does not check the validity of the data entered. It only checks whether all the fields of the form have been filled or not. For example, let’s suppose we have two text fields: Email and Password. form.is_submitted will return true if both fields have been filled by the user. It does not matter whether the user enters the correct or incorrect email and password. However, if one or both fields are empty, then ...