今天來看加減乘除法的部分，加法呢還是沿用我們的bmiclass

#bmiclass.py
class health:
    def __init__(self,h=0,w=0):
        self.height=h
        self.weight=w
    def BMI(self):
        return self.weight / ((self.height/100)**2)

實作覆寫掉對應的特殊方法!

__add__  +
__sub__  -
__mul__  *
__truediv__ /

依樣我們舉例子

把a同學和b同學的bmi互相加減乘除

        def __add__(self,other):
        return float(self.BMI()) + float(other.BMI())
        def __sub__(self,other):
        return float(self.BMI()) - float(other.BMI())
        def __mul__(self,other):
        return float(self.BMI()) * float(other.BMI())
        def __truediv__(self,other):
        return float(self.BMI()) / float(other.BMI())