WTForms is a popular Python library used for building and validating web forms. It simplifies the process of creating and handling forms in web applications, making it easier to collect user input and ensure data integrity.

Main features of WTForms include:

1. Declarative Syntax: WTForms allows you to define forms and fields using a simple and declarative syntax, making it easy to create forms without needing to write lengthy HTML or validation code.

2. Field Types: It provides a wide range of field types, such as StringField (for text input), IntegerField (for integer input), BooleanField (for checkboxes), TextAreaField (for multiline text input), and more.

3. Validation: WTForms allows you to add validation rules to each field, ensuring that the submitted data meets specific criteria (e.g., required, minimum length, valid email, etc.).

4. CSRF Protection: It comes with built-in support for Cross-Site Request Forgery (CSRF) protection to enhance the security of your forms.

5. Rendering: WTForms can render form fields into HTML, allowing you to easily display the form on your web pages.

Here’s a basic example of using WTForms:

In this example, we use WTForms to create a form with two fields: “username” and “email.” We apply validation rules to each field (minimum length for the username and a valid email format for the email). If the form is submitted via a POST request and passes validation, the data is processed accordingly.

Keep in mind that this example uses WTForms with Flask, but WTForms can also be used with other web frameworks in Python. The library is not tied exclusively to Flask.