allow cycles throught the __dict__ slot to be cleared (closes #1469629)
Patch from Armin, test from me.
diff --git a/Lib/test/test_descr.py b/Lib/test/test_descr.py
index 92304b4..4aeb77f 100644
--- a/Lib/test/test_descr.py
+++ b/Lib/test/test_descr.py
@@ -1,8 +1,10 @@
import builtins
+import gc
import sys
import types
import math
import unittest
+import weakref
from copy import deepcopy
from test import support
@@ -1186,7 +1188,6 @@
self.assertEqual(Counted.counter, 0)
# Test lookup leaks [SF bug 572567]
- import gc
if hasattr(gc, 'get_objects'):
class G(object):
def __eq__(self, other):
@@ -4380,7 +4381,6 @@
self.assertRaises(AttributeError, getattr, C(), "attr")
self.assertEqual(descr.counter, 4)
- import gc
class EvilGetattribute(object):
# This used to segfault
def __getattr__(self, name):
@@ -4429,6 +4429,21 @@
foo = Foo()
str(foo)
+ def test_cycle_through_dict(self):
+ # See bug #1469629
+ class X(dict):
+ def __init__(self):
+ dict.__init__(self)
+ self.__dict__ = self
+ x = X()
+ x.attr = 42
+ wr = weakref.ref(x)
+ del x
+ support.gc_collect()
+ self.assertIsNone(wr())
+ for o in gc.get_objects():
+ self.assertIsNot(type(o), X)
+
class DictProxyTests(unittest.TestCase):
def setUp(self):
class C(object):
diff --git a/Misc/NEWS b/Misc/NEWS
index 44683f5..119dfd7 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -10,6 +10,9 @@
Core and Builtins
-----------------
+- Issue #1469629: Allow cycles through an object's __dict__ slot to be
+ collected. (For example if ``x.__dict__ is x``).
+
- Issue #14172: Fix reference leak when marshalling a buffer-like object
(other than a bytes object).
diff --git a/Objects/typeobject.c b/Objects/typeobject.c
index c3822ab..e006694 100644
--- a/Objects/typeobject.c
+++ b/Objects/typeobject.c
@@ -830,8 +830,13 @@
assert(base);
}
- /* There's no need to clear the instance dict (if any);
- the collector will call its tp_clear handler. */
+ /* Clear the instance dict (if any), to break cycles involving only
+ __dict__ slots (as in the case 'self.__dict__ is self'). */
+ if (type->tp_dictoffset != base->tp_dictoffset) {
+ PyObject **dictptr = _PyObject_GetDictPtr(self);
+ if (dictptr && *dictptr)
+ Py_CLEAR(*dictptr);
+ }
if (baseclear)
return baseclear(self);