您需要的内容如下：

import datetime # imports the datetime library
x = str(datetime.datetime.now()) # sets a variable x to be the current datatime, converted to string format

with open("data.txt", 'w+') as f: # creates (or opens and will overwrite if already exists) the file data.txt and changes the reference to be f
   f.write(x) # writes to data.txt the contents of the x variable

上面代码的问题在于datetime.datetime.now()没有返回str类型，而是返回datetime.datetime类型，Python不能直接编写该类型。