>>> mydic={'a':1,'b':2}  
>>> mydic['a']  
1  
>>> mydic['c']  
Traceback (most recent call last):  
  File "<stdin>", line 1, in ?  
KeyError: 'c'  

>>> 'a' in mydic.keys()  
True  
>>> 'c' in mydic.keys()              #用in做成员归属测试  
False  
>>> D.get('c','"c" is not exist!')   #用get或获取键，如不存在，会打印后面给出的错误信息  
'"c" is not exist!'