Simple Bool field for WTForms, True for "set" False for "unset"

gistfile1.py

class RepeatForm(Form):
    action = TextField('Action', validators=[Required()])

    def validate_action(form, field):
        if field.data == "set":
            field.data = True
        elif field.data == "unset":
            field.data = False
        else:
            raise ValidationError("Invalid: should be set or unset.")