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