* http://learn.rmotr.com/python/introduction-to-programming-with-python/advanced-oop/simple-class-attribute
* http://learn.rmotr.com/python/introduction-to-programming-with-python/advanced-oop/class-and-instance-attributes
* http://learn.rmotr.com/python/introduction-to-programming-with-python/advanced-oop/cookie-factory
* http://learn.rmotr.com/python/introduction-to-programming-with-python/advanced-oop/cookie-factory-with-default-values
* http://learn.rmotr.com/python/introduction-to-programming-with-python/advanced-oop/class-counter