Python中字典的has_key方法在3.4版本中改为in

>>> a={1:'a',2:'b'}
>>> 1 in a
True
>>> 'a' in a
False
>>> 2 in a
True
>>> 

即可以判断某个键是否存在于字典中;

>>> a.has_key(1)
2 Traceback (most recent call last):
3   File "<pyshell#27>", line 1, in <module>
4     a.has_key(1)
5 AttributeError: 'dict' object has no attribute 'has_key'