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This documentation was last modified: Monday, April 16th, 2018 at 3:48 am

Fallback Skill

A Fallback Skill is a Skill that will be called if no Intent is matched to the Utterance. Previously, Wolfram Alpha was the only Fallback Skill, finding answers for general queries. Recently a system for multiple Fallback Skills was added.

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.

Creating a Fallback Skill

Import the FallbackSkill base class:

from mycroft.skills.core import FallbackSkill

Create a derived class:

class MeaningFallback(FallbackSkill):
    """
        A Fallback skill to answer the question about the
        meaning of life, the universe and everything.
    """
    def __init__(self):
        super(MeaningFallback, self).__init__(name='My Fallback Skill)
        # Add your own initialization code here

Register the handler with the fallback system

Note: a FallbackSkill can register any number of fallback handlers

    def initialize(self):
         """
             Registers the fallback handler
         """
         self.register_fallback(self.handle_fallback, 10)
         # Any other initialize code you like can be placed here

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

    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

Finally, the Skill creator must make sure the skill handler is removed when the Skill is shutdown by the system.

    def shutdown(self):
        """
            Remove this skill from list of fallback skills.
        """
        self.remove_fallback(self.handle_fallback)
        super(MeaningFallback, self).shutdown()

And as with a normal Skill the function create_skill() needs to be in the file to instantiate the skill.

def create_skill():
    return MeaningFallback()

The above example can be found here.


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