代码如下：

import datetime
def validate(date_text):
    try:
        datetime.datetime.strptime(date_text, '%Y-%m-%d')
    except ValueError:
        raise ValueError("Incorrect data format, should be YYYY-MM-DD")

>>> validate('2003-12-23')
>>> validate('2003-12-32')

第二个会产生exception如下：

 Traceback (most recent call last):  
 File "<pyshell#20>", line 1, in <module>
      validate('2003-12-32')   
 File "<pyshell#18>", line 5, in validate
      raise ValueError("Incorrect data format, should be YYYY-MM-DD")
 ValueError: Incorrect data format, should be YYYY-MM-DD