‘str’ object has no attribute ‘weekday’ Convert date to a string

date = datetime.datetime.today()
shift = datetime.timedelta(max(1,(date.weekday()+6)%7 - 3))
...

new_mail.Subject = 'XXXXXXX as of ' + (date - shift).strftime('%Y-%m-%d')

The problem is that you convert date to string initially and therefore cannot perform date arithmetic on it from there on.