Note 1 for <Pratical Programming : An Introduction to Computer Science Using Python 3>

Book Imformation :

<Pratical Programming : An Introduction to Computer Science Using Python 3> 2nd Edtion

Author : Paul Gries,Jennifer Campbell,Jason Montojo

Page : Chapter 1 and Chapter 2.1-2.2

1.every computer runs operating system,which it's the only program on the computer that's allowed direct access to the hardware(硬件).

or more complicate(add another layer between the programmer and the hardware) :

2.two ways to use the Python interpreter(解释器) :

(1).execute a saved Python program with .py extension(扩展，后缀)

(2).using a Python shell(壳，命令解析器)

3.the >>> symbol is called a prompt(提示),prompting you to type something

4.the result of interger division has a decimal point even is a whole number :

 >>> 5 / 2
 2.5
 >>> 4 / 2
 2.0

5.when the operands (操作数) are int and float,Python automatically convert the int into a float :

 >>> 17.0 - 10
 7.0
 >>> 17 - 10.0
 7.0

and you can omit zero like ‘17.’ (but most people think it is a bad idea)

6.integer division,modulo(取模)

 >>> 53 // 24
 2
 >>> 53 % 24
 5

//：整除

when the operands are negative or float,it takes the floor(向下取整) of the result.

 >>> -17 // 10
 -2
 >>> 17 // 10
 1

 >>> 3.5 // 1.0
 3.0
 >>> 3 // 1.1
 2.0
 >>> 3.3 // 1
 3.0

when using modulo,the sign of the result matches the divisor(除数)

定义：a % b = a - n*b，n为不超过a/b的整数

 >>> -17 % 10
 3
 >>> 17 % -10
 -3

7.exponentiation(取幂)：**

 >>> 2 ** 3
 8
 >>> 3 ** 3
 27

8.binary operators(双目运算符),unary operators(单目运算符)

+、-、*、/：binary operators

-(nagetive)：unary operators

 >>> -5
 -5
 >>> --5
 5
 >>> ---5
 -5