How can I create custom fields in Flask-WTF?

How can I create custom fields in Flask-WTF?

You can create custom fields in Flask-WTF by subclassing the Field class and implementing your own validation and rendering methods.

Can you give me an example of a custom field?

Sure! Here's a simple example of a custom field that validates a phone number:

from wtforms import Field

class PhoneNumberField(Field):
    def __init__(self, label=None, validators=None, **kwargs):
        super().__init__(label, validators, **kwargs)

    def process_formdata(self, valuelist):
        if valuelist:
            self.data = valuelist[0]
        else:
            self.data = None

    def pre_validate(self, form):
        if not self.data:
            raise ValidationError('Phone number is required.')
        # Add more validation logic here

How do I use this custom field in a form?

You can use the custom field in your form like this:

from flask_wtf import FlaskForm

class MyForm(FlaskForm):
    phone = PhoneNumberField('Phone Number')

What if I want to add custom rendering for the field?

You can override the __call__ method in your custom field class to define how it should be rendered in templates.