(self, trigger, func)
Add a new before or after callback to all available transitions.
        Args:
            trigger (str): The type of triggering event. Must be one of
                'before', 'after' or 'prepare'.
            func (str): The name of the callback function.
Add a new before or after callback to all available transitions.
        Args:
            trigger (str): The type of triggering event. Must be one of
                'before', 'after' or 'prepare'.
            func (str): The name of the callback function.
Add a new before or after callback to all available transitions . Args : trigger ( str ) : The type of triggering event . Must be one of before after or prepare . func ( str ) : The name of the callback function .
def add_callback(self, trigger, func):
        """ Add a new before or after callback to all available transitions.
        Args:
            trigger (str): The type of triggering event. Must be one of
                'before', 'after' or 'prepare'.
            func (str): The name of the callback function.
        """
        for trans in itertools.chain(*self.transitions.values()):
            trans.add_callback(trigger, func)
def add_callback ( self , trigger , func ) : for trans in itertools . chain ( * self . transitions . values ( ) ) : trans . add_callback ( trigger , func )