Q: After doing a del obj from a Python script where obj can be any Python object the destructor, __del__, of obj is never invoked.

Calling del on a Python object does not guarantee the destructor will be called! That simply decrements a counter internal to the object. It will invoke the destructor if (and only if) the internal counter, after it is decremented, has reached zero.

Q: Why doesn't the Python interpreter call the __del__ method of all Python objects contained within it before exiting?

There is not even a guarantee that the Python interpreter will invoke the destructors of all objects residing in it before exiting! This is part of the Python specification.

Workaround:

The only guaranteed way to ensure a destructor is called in Python is to call it in your own code like this: