def jia(x,y):    return x+ydef jian(x,y):    return x-ydef cheng(x,y):    return x*ydef chu(x,y):    return x/y#建一个字典，使得对应的运算符取到对应的运算方法：operator = {"+":jia,"-":jian,"*":cheng,"/":chu}def f(x,o,y):    #单独的看operator.get(o),其实就等于，jia,jian,cheng,chu 中的一种    print(operator.get(o)(x,y))f(4,"+",9)#switch 实现 加减乘除的方法！