字典的键值是"只读"的，所以不能对键和值分别进行初始化，即以下定义是错的：
>>> dic ={}
>>> dic.keys =(1,2,3,4,5,6)
Traceback(most recent call last):
File"", line 1,in
AttributeError:'dict'object attribute 'keys'is read-only
>>> dic.values =("a","b","c","d","e","f")
Traceback(most recent call last):
File"", line 1,in
AttributeError:'dict'object attribute 'values'is read-only
>>>
