python子类调用父类、重新定义主类的方法

#子类调用父类
class Calc:
    def __init__(self):
        self.data = []
    def append2(self, x):
          self.data.append(x)
          print(self.data)             

class Calc_child(Calc):
    def add(self, a, b):
        return a/b**2

c_child = Calc_child()
c_child.append2(4)
print(c_child.data)
print(c_child.add(4, 4))
'''
[4]
[4]
0.25
'''
#重新定义主类的方法 printBMI(self)
class BMI:
    def __init__(self,height,weight):
        self.bmi = weight/height**2
    def printBMI(self):
        print("Your BMI is {:.1f}".format(self.bmi))

class ChinaBMI(BMI):
    def printBMI(self):
        print("你的BMl是{:.1f}".format(self.bmi))
        if self.bmi < 18.5:
            print("偏瘦！")
        elif self.bmi < 24:
            print("稍瘦")
        elif self.bmi< 26:
            print("正常")
        elif self.bmi < 28:
            print("偏胖")
        else:
            print("肥胖")
            
h = float(input("height="))
w = float(input("wight="))
x = ChinaBMI(h,w)
x.printBMI()