Why aren't destructors guaranteed to be called on interpreter exit?

Question

From the python docs:

It is not guaranteed that __del__() methods are called for objects that still exist when the interpreter exits.

Answer 1

If you did some nasty things, you could find yourself with an undeletable object which python would try to delete forever:

class Phoenix(object):
    def __del__(self):
        print "Deleting an Oops"
        global a
        a = self

a = Phoenix()

Relying on __del__ isn't great in any event as python doesn't guarantee when an object will be deleted (especially objects with cyclic references). That said, perhaps turning your class into a context manager is a better solution ... Then you can guarantee that cleanup code is called even in the case of an exception, etc...