Hi Maciej,
On 04.09.2015 00:08, Maciej Fijalkowski wrote:
On Thu, Sep 3, 2015 at 9:23 AM, Valentine Sinitsyn
<valentine.sinit...@gmail.com> wrote:
Hi Armin,
On 25.08.2015 13:00, Armin Rigo wrote:
Hi Valentine,
On 25 August 2015 at 09:56, Valentine Sinitsyn
<valentine.sinit...@gmail.com> wrote:
Yes, I think so. There is a *highly obscure* corner case: __del__
will still be called several times if you declare your class with
"__slots__=()".
Even on "post-PEP-0442" Python 3.4+? Could you share a link please?
class X(object):
__slots__=() # <= try with and without this
def __del__(self):
global revive
revive = self
print("hi")
X()
revive = None
revive = None
revive = None
By accident, I found a solution to this puzzle:
class X(object):
__slots__ = ()
class Y(object):
pass
import gc
gc.is_tracked(X()) # False
gc.is_tracked(Y()) # True
An object with _empty_ slots is naturally untracked, as it can't create back
references.
Valentine
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That does not make it ok to have del called several time, does it?
That's a tricky question. Python's data model [1,2] doesn't say anything
about how many times __del__ can be called. PEP-0442 guarantees it will
be called only once, but it implicitly covers GC-objects only.
For me, it looks like destructor behaviour for non-GC object is
undefined, but I agree it makes sense to call them exactly once as well.
1. https://docs.python.org/3/reference/datamodel.html
2. https://docs.python.org/2/reference/datamodel.html
--
Valentine
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