[Python-Dev] PEP 442 clarification for type hierarchies

[Antoine Pitrou]

On Tue, 06 Aug 2013 18:38:51 +0200
Stefan Behnel <stefan_ml at behnel.de> wrote:
> Antoine Pitrou, 06.08.2013 17:49:
> > Le Tue, 06 Aug 2013 17:18:59 +0200,
> > Stefan Behnel a écrit :
> >> If a Python class with a
> >> __del__ inherits from an extension type that implements
> >> tp_finalize(), then whose tp_finalize() will be executed first?
> > 
> > Then only the Python __del__ gets called. It should call
> > super().__del__() manually, to ensure the extension type's
> > tp_finalize gets called.
> 
> Ok, but then all I have to do in order to disable C level finalisation for
> a type is to inherit from it and provide an empty __del__ method.
> 
> I think that disqualifies the feature for the use in Cython. Finalisation
> at the Python level is nice, but at the C level it's usually vital. I had
> originally read this PEP as a way to get better guarantees than what
> dealloc can provide, but your above statement makes it rather the opposite.

Anything vital should probably be ensured by tp_dealloc.
For example, you might close an fd early in tp_finalize, but also ensure
it gets closed in tp_dealloc in the case tp_finalize wasn't called.

(that said, you can also have fd leaks in pure Python...)

Regards

Antoine.