a problem in datetime.interval()

[lameck kassana]

hi ,
I am writing a scriot which will move old files from one directory to backup
The files are in mode *20090307* mean *yyyymmmdd* to new files.
The script is below is like this

*import os
import datetime
import time
from datetime import date
today=date.today()*
*for x in range(5,10):
    interval=datetime.timedelta(x)
    print interval
    today=today-interval
    today=today.strftime("%Y%m%d")
    print today
    src=r"f:\Sql_Loader\SMR\file_log_backup\smr"+today+"*"
    dest=r" f:\Sql_Loader\SMR\file_log_backup2"
    print src
    print dest
    os.system(r"move " +src+" "+ dest)*



but the error is like that
*Traceback (most recent call last):
  File "remove_old_files.py", line 10, in <module>
    today=today-interval
TypeError: unsupported operand type(s) for -: 'str' and 'datetime.timedelta'
*

It seems datetime.timedelta()does not respond with my loop
Any help??
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