From 54fc92c9bfd9471350c8ef4ceb45bc1139d77597 Mon Sep 17 00:00:00 2001
From: Graham Dumpleton <Graham.Dumpleton@gmail.com>
Date: Fri, 13 Sep 2013 16:39:11 +1000
Subject: [PATCH] Added a weakref proxy implementation that works with both
 normal functions and instance methods.

---
 src/__init__.py |  2 +-
 src/wrappers.py | 64 +++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 65 insertions(+), 1 deletion(-)

diff --git a/src/__init__.py b/src/__init__.py
index 2356f7a..dfdf254 100644
--- a/src/__init__.py
+++ b/src/__init__.py
@@ -1,5 +1,5 @@
 __version_info__ = ('1', '1', '0')
 __version__ = '.'.join(__version_info__)
 
-from .wrappers import ObjectProxy, FunctionWrapper
+from .wrappers import ObjectProxy, FunctionWrapper, WeakFunctionProxy
 from .decorators import decorator
diff --git a/src/wrappers.py b/src/wrappers.py
index f6fbe49..d1e35c8 100644
--- a/src/wrappers.py
+++ b/src/wrappers.py
@@ -2,6 +2,7 @@ from . import six
 
 import functools
 import operator
+import weakref
 
 class _ObjectProxyMethods(object):
 
@@ -511,3 +512,66 @@ try:
     from ._wrappers import ObjectProxy, FunctionWrapper
 except ImportError:
     pass
+
+def _weak_function_proxy_callback(ref, self, callback):
+    if self._self_expired:
+        return
+
+    self._self_expired = True
+
+    # This could raise an exception. We let it propagate back and let
+    # the weakref.proxy() deal with it, at which point it generally
+    # prints out a short error message direct to stderr and keeps going.
+
+    if callback is not None:
+        callback(self)
+
+class WeakFunctionProxy(ObjectProxy):
+
+    def __init__(self, wrapped, callback=None):
+        # We need to determine if the wrapped function is actually a
+        # bound method. In the case of a bound method, we need to keep a
+        # reference to the original unbound function and the instance.
+        # This is necessary because if we hold a reference to the bound
+        # function, it will be the only reference and given it is a
+        # temporary object, it will almost immediately expire and
+        # the weakref callback triggered. So what is done is that we
+        # hold a reference to the instance and unbound function and
+        # when called bind the function to the instance once again and
+        # then call it. Note that we avoid using a nested function for
+        # the callback here so as not to cause any odd reference cycles.
+
+        _callback = callback and functools.partial(
+                _weak_function_proxy_callback, self=self, callback=callback)
+
+        self._self_expired = False
+
+        try:
+            self._self_instance = weakref.proxy(wrapped.__self__, _callback)
+
+            super(WeakFunctionProxy, self).__init__(
+                    weakref.proxy(wrapped.__func__, _callback))
+
+        except AttributeError:
+            self._self_instance = None
+
+            super(WeakFunctionProxy, self).__init__(
+                    weakref.proxy(wrapped, _callback))
+
+    def __call__(self, *args, **kwargs):
+        # We perform a boolean check here on the instance and wrapped
+        # function as that will trigger the reference error prior to
+        # calling if the reference had expired.
+
+        instance = self._self_instance and self._self_instance
+        function = self._self_wrapped and self._self_wrapped
+
+        # If the wrapped function was originally a bound function, for
+        # which we retained a reference to the instance and the unbound
+        # function we need to rebind the function and then call it. If
+        # not just called the wrapped function.
+
+        if instance is None:
+            return self._self_wrapped(*args, **kwargs)
+
+        return function.__get__(instance)(*args, **kwargs)