# HG changeset patch
# User Denis Laxalde <denis.laxalde@logilab.fr>
# Date 1511971685 -3600
# Node ID 24393ce335f5b97cd546000a87c5c87a48d1a15a
# Parent  55924e962cd7190f5d060722f50eac6d30552deb
[gcdebug] Only ignore weakref.WeakKeyDictionary class on Python 2

From Python 3.5, this class fails isinstance check with the following
error:

::

    cls = <class 'weakref.WeakKeyDictionary'>, instance = <functools._lru_list_elem object at 0x7f4331859a48>

        def __instancecheck__(cls, instance):
            """Override for isinstance(instance, cls)."""
            # Inline the cache checking
    >       subclass = instance.__class__
    E       AssertionError: [<class 'AttributeError'> in gc] 'functools._lru_list_elem' object has no attribute '__class__'

    /usr/lib/python3.5/abc.py:181: AssertionError


I have no clue why this happens, but it makes
cubicweb.web.test.test_views.AutomaticWebTest.test_startup_views fail on
Python 3.5. So only consider this class for Python 2.

diff -r 55924e962cd7 -r 24393ce335f5 cubicweb/_gcdebug.py
--- a/cubicweb/_gcdebug.py	Wed Nov 29 16:14:57 2017 +0100
+++ b/cubicweb/_gcdebug.py	Wed Nov 29 17:08:05 2017 +0100
@@ -19,6 +19,8 @@
 
 import gc, types, weakref
 
+from six import PY2
+
 from cubicweb.schema import CubicWebRelationSchema, CubicWebEntitySchema
 try:
     from cubicweb.web.request import _NeedAuthAccessMock
@@ -29,12 +31,16 @@
 
 IGNORE_CLASSES = (
     type, tuple, dict, list, set, frozenset, type(len),
-    weakref.ref, weakref.WeakKeyDictionary,
+    weakref.ref,
     listiterator,
     property, classmethod,
     types.ModuleType, types.FunctionType, types.MethodType,
     types.MemberDescriptorType, types.GetSetDescriptorType,
     )
+if PY2:
+    # weakref.WeakKeyDictionary fails isinstance check on Python 3.5.
+    IGNORE_CLASSES += (weakref.WeakKeyDictionary, )
+
 if _NeedAuthAccessMock is not None:
     IGNORE_CLASSES = IGNORE_CLASSES + (_NeedAuthAccessMock,)