[Python-Dev] __del__ is not called after creating a new reference
oleg at redhat.com
Sun Apr 2 13:20:14 EDT 2017
On 04/02, Armin Rigo wrote:
> Hi all,
> On 20 March 2017 at 22:28, Nathaniel Smith <njs at pobox.com> wrote:
> > Modern CPython, and all extant versions of PyPy and Jython, guarantee that
> > __del__ is called at most once.
> Just a note, if someone actually depends on this: it is not true in
> all cases. For example, in CPython 3.5.3:
> >>> class X:
> ... __slots__=() # <= note this!
> ... def __del__(self):
> ... print("DEL")
> ... global resurrect
> ... resurrect = self
> >>> print(X())
> <__main__.X object at 0x7f5d1ad600d0>
> >>> resurrect=None
/* Enable GC unless this class is not adding new instance variables and
the base class did not use GC. */
if ((base->tp_flags & Py_TPFLAGS_HAVE_GC) ||
type->tp_basicsize > base->tp_basicsize)
type->tp_flags |= Py_TPFLAGS_HAVE_GC;
That is. "type->tp_basicsize > base->tp_basicsize" is false if empty __slots__,
so we do not set HAVE_GC.
And PyObject_CallFinalizer() doesn't set FINALIZED if PyType_IS_GC(tp) == F.
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