(self, trigger, func)
Add a new before, after, or prepare callback.
        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, after, or prepare callback.
        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 after or prepare callback . 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, after, or prepare callback.
        Args:
            trigger (str): The type of triggering event. Must be one of
                'before', 'after' or 'prepare'.
            func (str): The name of the callback function.
        """
        callback_list = getattr(self, trigger)
        callback_list.append(func)
def add_callback ( self , trigger , func ) : callback_list = getattr ( self , trigger ) callback_list . append ( func )