1、" ** "优先级高于" - "
[1] Since ** has higher precedence than -, -3**2 will be interpreted as -(3**2) and thus result in -9. To avoid this and get 9, you can use (-3)**2.
2、单个引号使用，示例 ' " ' 和" ' “ 是可以的，反之需要‘ \’ ' 和”\“' 标注
[2] Unlike other languages, special characters such as \n have the same meaning with both single ('...') and double ("...") quotes. The only difference between the two is that within single quotes you don’t need to escape " (but you have to escape \') and vice versa.
3、多个表达式总从 从右往左执行，单个表达式内是从左往右执行
示例：a,b = 0,1 执行顺序为
b = 1
a = 0
再如：a , b = b , a + b 执行顺序为：
b = a + b
a = b
The first line contains a multiple assignment: the variables a and b simultaneously get the new values 0 and 1. On the last line this is used again, demonstrating that the expressions on the right-hand side are all evaluated first before any of the assignments take place. The right-hand side expressions are evaluated from the left to the right.
4、对（字符串）列表操作（（for,while）一定要以副本，否则会产生死循环。
If you need to modify the sequence you are iterating over while inside the loop (for example to duplicate selected items), it is recommended that you first make a copy. Iterating over a sequence does not implicitly make a copy. The slice notation makes this especially convenient:
>>> for w in words[:]: # Loop over a slice copy of the entire list.
... if len(w) > 6:
... words.insert(0, w)
...
>>> words
['defenestrate', 'cat', 'window', 'defenestrate']
