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"""Finalization with weakrefs

This is designed for avoiding __del__.
"""


import sys
import traceback
import weakref


__author__
= "Benjamin Peterson <benjamin@python.org>"


class OwnerRef(weakref.ref):
   
"""A simple weakref.ref subclass, so attributes can be added."""
   
pass


def _run_finalizer(ref):
   
"""Internal weakref callback to run finalizers"""
   
del _finalize_refs[id(ref)]
    finalizer
= ref.finalizer
    item
= ref.item
   
try:
        finalizer
(item)
   
except Exception:
       
print("Exception running {}:".format(finalizer), file=sys.stderr)
        traceback
.print_exc()


_finalize_refs
= {}


def track_for_finalization(owner, item, finalizer):
   
"""Register an object for finalization.

    ``owner`` is the the object which is responsible for ``item``.
    ``finalizer`` will be called with ``item`` as its only argument when
    ``owner`` is destroyed by the garbage collector.
    """

   
ref = OwnerRef(owner, _run_finalizer)
   
ref.item = item
   
ref.finalizer = finalizer
    _finalize_refs
[id(ref)] = ref

Diff to Previous Revision

--- revision 2 2010-05-23 22:03:43
+++ revision 3 2011-07-02 18:42:08
@@ -16,18 +16,19 @@
     
pass
 
 
-def _run_finalizers(ref):
+def _run_finalizer(ref):
     
"""Internal weakref callback to run finalizers"""
-    errors = []
-    for item, callback in ref.to_finalize:
-        try:
-            callback(item)
-        except Exception:
-            errors.append((callback, sys.exc_info()))
-    for callback, error in errors:
-        print("Exception running {}:".format(callback), file=sys.stderr)
-        traceback.print_exception(*error)
-    del errors # Clear cycles from sys.exc_info()
+    del _finalize_refs[id(ref)]
+    finalizer = ref.finalizer
+    item = ref.item
+    try:
+        finalizer(item)
+    except Exception:
+        print("Exception running {}:".format(finalizer), file=sys.stderr)
+        traceback.print_exc()
+
+
+_finalize_refs = {}
 
 
 
def track_for_finalization(owner, item, finalizer):
@@ -37,9 +38,7 @@
     
``finalizer`` will be called with ``item`` as its only argument when
     
``owner`` is destroyed by the garbage collector.
     
"""
-    try:
-        ref = owner._owner_ref
-    except AttributeError:
-        ref = owner._owner_ref = OwnerRef(owner, _run_finalizers)
-        ref.to_finalize = []
-    ref.to_finalize.append((item, finalizer))
+    ref = OwnerRef(owner, _run_finalizer)
+    ref.item = item
+    ref.finalizer = finalizer
+    _finalize_refs[id(ref)] = ref

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