2018-01-24 chp07的date变量 ，如何做validation，程序改进

The slightly counterintuitive workaround is to convert the string input we receive

from the user to a datetime object and then back to a string (which will always be in

the correct format) before passing it into our database code to store in MySQL.

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First off, add the following helper function to your crimemap.py file:

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def format_date(userdate):

date = dateparser.parse(userdate)        --// 旁白： 先转成 date-object   

try:

return datetime.datetime.strftime(date, "%Y-%m-%d")   -- // 果然如上面 所言，从 date-object 再转成  字符型 

注意 ：  datetime.datetime.strftime （striFtime）是经典的  

由字符串转为日期型的函数为：datetime.datetime.strptime()，