[Python-3000] Removing __del__

[Marcin 'Qrczak' Kowalczyk]

"Giovanni Bajo" <rasky at develer.com> writes:

> What if the "self" passed to __del__ was instead a weakref.proxy,
> or a similar wrapper object which does not give you access to the
> object itself but lets you access its attributes?

weakref.proxy will find the object already dead.

I doubt this can be done fully automatically.

The basic design is splitting the object into an outer part handled to
clients, which is watched to become unreachable, and a private inner
part used to physically access the resource, including releasing it.
I see no good way around it.

Often the inner part is a single field which is already separated.
In other cases it might require an extra indirection, in particular
if it's a mutable field.

This design distinguishes between related objects which are needed
during finalization (fields of the inner object) and related objects
which are not (fields of the outer object).

Cycles involving only outer objects are harmless, they can be safely
freed together, triggering finalization of all associated objects.
Inner objects may also refer to most other objects, ensuring that
they are not finalized earlier. But a path from an inner object to its
associated outer object prevents it from being finalized and is a bug
in the program (unless it is broken before the object loses all other
references).

-- 
   __("<         Marcin Kowalczyk
   \__/       qrczak at knm.org.pl
    ^^     http://qrnik.knm.org.pl/~qrczak/