python input eval函数

1、题目：计算某同学语文、数学、英语三门课程的平均分
代码如下：

name=input("please enter your name:")
chi=eval(input("please enter your chinese score:"))
math=eval(input("please enter your math score:"))
eng=eval(input("please enter your English:"))
aver=(chi+math+eng)/3
print(name,",your average score is",aver)

运行结果:
please enter your name:da bao
please enter your chinese score:90
please enter your math score:80
please enter your English:70
da bao ,your average score is 80.0

2、题目：从键盘输入半径，求球体的表面积和体积。
代码如下：

r=eval(input("please enter the radius of sphere:"))
s=4*3.14*(r**2)
v=(4/3)*3.14*(r**3)
print("the surface area of sphere is",s)
print("the volume of sphere is",v)

运行结果：
please enter the radius of sphere:2
the surface area of sphere is 50.24
the volume of sphere is 33.49333333333333

知识点：
input()函数：用户从键盘输入
①字符，保存到一个变量里
或②数字，用eval()函数把包含数字的字符串转换成有效的数字

x的平方用x2
x的3次方用x3