Re: [Python-Dev] del is not called after creating a new reference

2 Apr 2017

      On 04/02, Armin Rigo wrote:
...
Hi all,
On 20 March 2017 at 22:28, Nathaniel Smith <njs@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>
DEL
resurrect=None
DEL
Objects/typeobject.c:type_new()

    /* 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.

Oleg.

Re: [Python-Dev] __del__ is not called after creating a new reference

Oleg Nesterov

Re: [Python-Dev] del is not called after creating a new reference