python - What happens if you delete an object that holds another object?

Question

If I have

class MyClass:
    def __init__(self, object):
        self.object = object
some_other_object = SomeOtherObject()
myclass = MyClass(some_other_object)
del myclass

what happens to the some_other_object? Does it get deleted too?

question from:https://stackoverflow.com/questions/65646995/what-happens-if-you-delete-an-object-that-holds-another-object

Answer 1

If there are no other references to some_other_object throughout the program, then yes, it too will get deleted.

In your case, there are two references: 1) some_other_object, and 2) myclass.object.

Deleting myclass just deletes the second reference. But the first remains.

Python uses a method of garbage collection called 'reference counting'. To summarise it very concisely, Python keeps track of the number of 'references' to each object in memory. If you run del x, you're decrementing the number of references to the object that x referred to by 1 (and the name x no longer refers to that object, of course). Once the number of references to an object reaches 0, it can be garbage collected (i.e. the memory it occupies can be freed).