How can I create custom validators in Flask?

How can I create custom validators in Flask?

You can create custom validators in Flask by defining a function that checks the input and raising a validation error if needed.

Can you show me an example of a custom validator?

Sure! Here's a simple example:

from flask_wtf import FlaskForm
from wtforms import StringField, ValidationError

class MyForm(FlaskForm):
    name = StringField('Name')

    def validate_name(form, field):
        if len(field.data) < 3:
            raise ValidationError('Name must be at least 3 characters long.')

What if I want to validate an email address?

You can create a custom validator for email like this:

def validate_email(form, field):
    if '@' not in field.data:
        raise ValidationError('Invalid email address.')

How do I integrate this validator into my form?

You can integrate it by adding the validate_<fieldname> method in your form class, just like the name validator.