字典的方法

fromkeys(S[,v])  方法: 　　创建并返回新的字典

New dict with keys from S and values equal to v(v defaults to None).

eg:

>>>dict1 = {}

>>>dict1.fromkeys((1,2,3))　　　　#创建只有键的字典，value默认为None

1: None, 2: None, 3: None}

>>>dict1.fromkeys((1,2,3),'Number')　　　　#每一个value都是‘Number’

{1: 'Number', 2: 'Number', 3: 'Number'}

>>>dict1.fromkeys((1,2,3),('one','two','three'))　　　　#不会一一对应

{1: ('one', 'two', 'three'), 2: ('one', 'two', 'three'), 3: ('one', 'two', 'three')}

>>>dict1.fromkeys((1,3),'shuzi')　　　　#重新建立一个新的字典dict1 

{1: 'shuzi', 3: 'shuzi'}

#------------------------------------------------------------------------------------------------------------#

.clear() ：  清除字典内容，比给字典赋空要好

>>> dict1
{1: ('one', 'two', 'three'), 2: ('one', 'two', 'three'), 3: ('one', 'two', 'three')}
>>> dict1.clear()
>>> dict1
{}
>>> dict1 = {}
>>> dict1
{}

>>> a = {'name':'abc'}
>>> b = a
>>> a = {}
>>> b
{'name': 'abc'}
>>> a = b
>>> a.clear()
>>> b
{}