jcorpac Flask Forms & Validation
User input is the most dangerous part of a web app. Flask-WTF provides a secure, Pythonic layer of protection.
Form Definitions
- WTForms: Define forms as Python classes (e.g.,
LoginForm(FlaskForm)). - Validators: Use
DataRequired(),Email(),Length(), and custom methods to ensure data integrity.
CSRF Protection
Flask-WTF automatically handles Cross-Site Request Forgery tokens. Ensure {{ form.hidden_tag() }} is present in your templates.
File Uploads
Use FileField and FileRequired with secure_filename() to safely handle user-uploaded media.
Best Practices
- Feedback: Display clear error messages next to invalid fields using
form.errors. - POST/Redirect/GET Pattern: Always redirect after a successful form submission to prevent duplicate data.