Вопрос наследования Python

Общее правило будет параметром.

Вопрос: is- a vs. has- a:

 Is the box a grid? 
     yes: # if so, then is it really a box???
         The box should inherit grid
     no:
         The box should get a reference to the grid 
            #(generally through a setter or constructor parameter).

Изменить

Пример:

class Grid:
    def __init__(self,width=1,height=1):
        this.width = width; this.height = height;

    def getDimensions(self):
        return (this.width, this.height)

class Box:
    def __init__(self, grid):
        this.__grid = grid; this.x = 0; this.y = 0            

    def verify(self):
        width, height = this.__grid.dimensions()
        if this.x < width and this.y < height:
             print( "A-OK!" ); 
        else
             print( "I am off the grid!!!" )


grid = Grid();
box = Box(grid);
box.verify();