form_validate.py

def validate(self,
                 dispatcher: CollectingDispatcher,
                 tracker: Tracker,
                 domain: Dict[Text, Any]) -> List[Dict]:
    """Validate extracted requested slot
            else reject the execution of the form action
    """
    # extract other slots that were not requested
    # but set by corresponding entity
    slot_values = self.extract_other_slots(dispatcher, tracker, domain)

    # extract requested slot
    slot_to_fill = tracker.get_slot(REQUESTED_SLOT)
    if slot_to_fill:
        slot_values.update(self.extract_requested_slot(dispatcher,
                                                       tracker, domain))
        if not slot_values:
            # reject form action execution
            # if some slot was requested but nothing was extracted
            # it will allow other policies to predict another action
            raise ActionExecutionRejection(self.name(),
                                           "Failed to validate slot {0}"
                                           "with action {1}"
                                           "".format(slot_to_fill,
                                                         self.name()))

    # we'll check when validation failed in order
    # to add appropriate utterances
    for slot, value in slot_values.items():

        if slot == 'num_people':
            if not self.is_int(value) or int(value) <= 0:
                dispatcher.utter_template('utter_wrong_num_people',
                                              tracker)
                # validation failed, set slot to None
                slot_values[slot] = None