(cls, _id)
This method should return an instance of this class matching the passed
        id, or None if not found.
This method should return an instance of this class matching the passed
        id, or None if not found.
This method should return an instance of this class matching the passed id or None if not found .
def get_obj_by_id(cls, _id):
        """
        This method should return an instance of this class matching the passed
        id, or None if not found.
        """
        raise NotImplementedError("Please implement this method.")
def get_obj_by_id ( cls , _id ) : raise NotImplementedError ( "Please implement this method." )