Fallback Skill

Order of precedence

The Fallback Skills all have a priority and will be checked in order from low priority value to high priority value. If a Fallback Skill can handle the Utterance it will create a response and return True.

After this no other Fallback Skills are tried. This means the priority for Fallbacks that can handle a broad range of queries should be high (80-100) and Fallbacks that only responds to a very specific range of queries should be higher (20-80). The more specific, the lower the priority value.

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Fallback Handlers

Import the FallbackSkill base class, create a derived class and register the handler with the fallback system

Implement the fallback handler (the method that will be called to potentially handle the Utterance).

The method implements logic to determine if the Utterance can be handled and shall output speech if it can handle the query.

It shall return Boolean True if the Utterance was handled and Boolean False if not.

from ovos_workshop.skills.fallback import FallbackSkill

class MeaningFallback(FallbackSkill):
    """
        A Fallback skill to answer the question about the
        meaning of life, the universe and everything.
    """
    def initialize(self):
         """
             Registers the fallback handler
         """
         self.register_fallback(self.handle_fallback, 10)
         # Any other initialize code you like can be placed here

    def handle_fallback(self, message):
        """
            Answers question about the meaning of life, the universe
            and everything.
        """
        utterance = message.data.get("utterance")
        if 'what' in utterance
            and 'meaning' in utterance
            and ('life' in utterance
                or 'universe' in utterance
                or 'everything' in utterance):
            self.speak('42')
            return True
        else:
            return False

NOTE: a FallbackSkill can register any number of fallback handlers

The above example can be found here.

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Decorators

Alternatively, you can use decorators

from ovos_workshop.decorators.fallback_handler import fallback_handler


class MeaningFallback(FallbackSkill):
    """
        A Fallback skill to answer the question about the
        meaning of life, the universe and everything.
    """

    @fallback_handler(priority=10)
    def handle_fallback(self, message):
        """
            Answers question about the meaning of life, the universe
            and everything.
        """
        utterance = message.data.get("utterance")
        if 'what' in utterance
            and 'meaning' in utterance
            and ('life' in utterance
                or 'universe' in utterance
                or 'everything' in utterance):
            self.speak('42')
            return True
        else:
            return False

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Check utterances

Fallback skills should report if they are able to answer a question, without actually executing any action.

Besides providing performance improvements this allows other OVOS components to check how a utterance will be handled without side effects

    def can_answer(self, utterances: List[str], lang: str) -> bool:
        """
        Check if the skill can answer the particular question. Override this
        method to validate whether a query can possibly be handled. By default,
        assumes a skill can answer if it has any registered handlers
        @param utterances: list of possible transcriptions to parse
        @param lang: BCP-47 language code associated with utterances
        @return: True if skill can handle the query
        """
        return len(self._fallback_handlers) > 0