from models.database import TodoState from wtforms import ValidationError from wtforms.validators import InputRequired class CheckTodoDateByState: def __init__(self): pass def __call__(self, form, field): try: todostate = TodoState(field.data) if todostate.needs_date(): date_check = InputRequired("Dieser Status benötigt ein Datum.") form.date.errors = [] date_check(form, form.date) except ValueError: raise ValidationError("Invalid state.")