1.variables must stary with a letter or underscore_

CASE sensitive!!

2. ** power

% remainder

/ 不是整数除法，就是正常的除 （in python 3） python2 和 c++一样还是整数除法

x = 1 + 2**3/4*5

print(x) //1+8/4 *5 =1+2*5 =11.0

1+1.0 // 2.0 - to float automatically

3.constans:fixed vlues such as numbers, letters and strings are constants

string constants use single quotes ('') or double quotes ("")

4. try/except -- traceback

try 里面任意一个die了直接走except，不会继续走下面的了--利用try来尝试危险，catch errors

astr = ‘hello bob'

try:

ister = int (astr)

except:

ister = -1 // usualy provide hints for where is wrong, can add a quit here

5.

name = input('who are u?) // the input() will return a string

print ('welcome', name) // the comma will creat a space

6. use # for comments in python

7. python use indent to distinguish block, which is 4 spaces, it is better to use space than tab, to avoid difference between different editors

8. python 里的print（） 有自动换行功效