We want to know when the instances of the Rectangle class are removed from memory, that is, when the objects become inaccessible and get deleted by the garbage-collection mechanism. However, it is very important to notice that the ways in which garbage collection works depends on the implementation of Python. Remember that, Python runs on a wide variety of platforms.

Before Python removes an instance from memory, it calls the __del__ method. Thus, we can use this method to add any code we want to run before the instance is destroyed. We can think of the __del__ method as the equivalent of a destructor in other object-oriented programming languages.

The following lines declare a __del__ method within the body of the Rectangle class. Remember that Python always receives self as the first argument for any instance method:

def __del__(self):
        print('A Rectangle instance is being destroyed.')

The following lines create two instances of the Rectangle class...