how soon is `__del__` called after reference count drops to zero?

Question

How soon after the reference count reaches zero is __del__ method called? Does the language promise that it\'s done right away, before any other use code can ex

Answer 1

Python doesn't make any guarantees about when __del__ is called, or whether it is called at all. As it is, __del__ methods are unlikely to be called if the object is part of a reference cycle, because even if the cycle as a whole is cleaned up, Python has no way to decide where to break the cycle and in what order the __del__ methods (if any) should be called. Because of __del__'s rather quirky semantics (in order to call __del__ the refcount of the object is temporarily increased, and the __del__ method can prevent destruction of the object by storing the reference somewhere else) what happens in other implementations is a bit of a crapshoot. (I don't remember the exact details in current Jython, but it has changed a few times in the past.)

That said, in CPython, if __del__ is called, it's called as soon as the reference count drops to zero (since refcounting is the only way __del__ methods are called, and the only chance CPython has of calling __del__ is when the actual refcount is changed.)