#!/usr/bin/env python3
 
from abc import ABCMeta, abstractmethod
class Shape_(metaclass=ABCMeta):
    @abstractmethod
    def calc_(self):
        pass
class Shape(metaclass=ABCMeta):
    @abstractmethod
    def calc(self):
        pass
class Rect(Shape):
    def __init__(self, w, h):
        self.w = w
        self.h = h
    def calc(self):
        area = self.w * self.h
        print('area rect:', area)        
class Circle(Shape):
    def __init__(self, r):
        self.r = r
    def calc(self):
        area = self.r * self.r * 3.14
        print('area circle: ', area)
      
class AreaCalc:
    def calc(self, shape):
        # if isinstance(shape, Shape_):     # wrong
        if isinstance(shape, Shape):        # right
            shape.calc()
        else:
            raise Exception('wrong interface') 
circle = Circle(2)
rect = Rect(4, 2)
areaCalc = AreaCalc()
areaCalc.calc(rect)
areaCalc.calc(circle)

class AreaCalc() {
	calc(shape: Shape) {
		shape.calc()
	}	
}