How can I create custom fields in WTForms?

How can I create custom fields in WTForms?

You can create custom fields in WTForms by subclassing the existing field classes. What type of custom field do you need?

I want to create a field that validates a phone number format.

You can create a custom field by subclassing StringField and adding your validation logic. Would you like a code example?

Yes, please provide a code example.

Here's a simple example:

from wtforms import StringField, ValidationError

class PhoneNumberField(StringField):
    def __init__(self, *args, **kwargs):
        super().__init__(*args, **kwargs)

    def pre_validate(self, form):
        if not self.data.isdigit() or len(self.data) != 10:
            raise ValidationError('Invalid phone number format.')