python多态

#对于弱类型的语言来说, 变量没有申明类型,因此同一个变量完全可以再不同的事件引用不同的对象,当同一个变量再调用同一个方法时候,完全可以呈现出多种行为
#这就是多态
#DrawCanvas的draw_canvas方法传入一个shape参数,该方法就是调用shape参数的draw方法,将自己绘制再画布上
class DrawCanvas:
    def draw_canvas(self,shape):
        shape.draw(self)

class Rectangle:
    def draw(self,canvas):
        print ("draw rectangle in %s" % canvas)

class Triangle:
    def draw(self,canvas):
        print "draw triangle in %s" % canvas

class Circle:
    def draw(self,canvas):
        print "draw circle in %s" % canvas

c = DrawCanvas()
c.draw_canvas(Rectangle())
c.draw_canvas(Triangle())
c.draw_canvas(Circle())

draw rectangle in <__main__.DrawCanvas instance at 0x0000000003815B88>
draw triangle in <__main__.DrawCanvas instance at 0x0000000003815B88>
draw circle in <__main__.DrawCanvas instance at 0x0000000003815B88>