Timer object in Django
Fork it. Have your model use three states for a product: available, taken, and purchased. When a user initiates an action that marks the product as taken, spawn a new process that will mark the product to available in 3 minutes if it is not purchased.
I'm using Django to create registration/payment application for a limited number of products.    I want to create a timer so that when a user chooses to purchase a product, that product will then displayed as "already taken".  But, if the user the user does not go through with the purchase and the timer runs out, the product goes back to status "available".  If the user completes the purchase, the timer should cancel, leaving the product's status permanently as "already taken".  
I've tried using python's dictionary to instantiate python Timer objects of the fly, but about 30% of the time, I get a "key error" when it's time to cancel the Timer.  
Please.  Could someone give me an idea on the proper way to do this in Django?
Thanks very much!
Mark