From Scratch: Flask Form Handling and WTForms Validation

This article introduces the core knowledge of handling forms in Flask using the Flask-WTF extension. Flask-WTF is built on WTForms and provides form creation, validation, and CSRF protection. For environment preparation, install `flask` and `flask-wtf`. The core is defining form classes that inherit from `FlaskForm`, using field types like `StringField` and `PasswordField`, and pairing them with validators such as `DataRequired` and `Email` to define rules (e.g., non-empty, format, length). In view functions, instantiate the form and use `form.validate_on_submit()` to handle POST requests and validate data integrity. Templates should use `form.hidden_tag()` to generate CSRF tokens and loop through `form.xxx.errors` to display error messages. After successful validation, retrieve data from `form.xxx.data` and combine it with database storage (e.g., SQLAlchemy). Key process: Define form class → View processing → Template rendering → Data validation and processing. Use WTForms validators to implement checks for non-empty, format, etc., combined with CSRF protection for security, enabling rapid construction of reliable form systems.