■ 运算符：
●赋值运算符
◆ "=" "+=" "-=" "*=" "/=" "%="
x=y=z=1 # 多重赋值
(x, y, z) = (1, 2, 'a string') #多元赋值
●算术运算符
◆ "+" "-" "*" "/" "//" "%" "**"
●关系运算符
◆ "<" ">" "<=" ">=" "!=" "=="
●逻辑运算符
◆ "or" "and" "not"
■ 表达式是将不同数据（包括变量、函数）用运算符号按一定规则连接起来的一种式子
a=int(raw_input("please input num1"))
b=int(raw_input("please input num2"))
print a+b
print a-b
print a*b
print a/b