deleting old folders with datetime function

I am trying to delete old folders and I am asking does anyone know how to set 开发者_开发知识库up a variable that allows me to check the variable 'todaystr' which is today's date and minus 7 days of this string and store it another variable. I am wanting to automatically delete old files after a week. Below shows the variable 'todaystr' being set up.

todaystr = datetime.date.today().isoformat()  

I would like to create a variable 'oldfile' that stores the current date minus 7 days so I can delete the file with this date. Thanks for any help.

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import datetime
import os
import shutil

threshold = datetime.datetime.now() + datetime.timedelta(days=-7)
file_time = datetime.datetime.fromtimestamp(os.path.getmtime('/folder_name'))

if file_time < threshold:
    shutil.rmtree('/folder_name')

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I relation to the above answer it works very well, the code I used was different in the end. I create the name of the folder with the current date, so when the nightly build runs it will only delete the folder named from 7 days ago. The code is as follows:

import datetime  
import os  
import calendar  

today = datetime.date.today()
todaystr = datetime.date.today().isoformat()
minus_seven = today.replace(day=today.day-7).isoformat()


if os.path.exists(minus_seven):
    os.system("sudo rm -rf "+minus_seven)
    print 'Sandboxes from 7 days ago removed'

I used linux the delete the folder as I have some linux incorporated into my code and it runs good like this.