* wpylib.py.im_weakref: weakref for instance method.

Copied from Linux Screen Reader project.

py/im_weakref.py

@@ -0,0 +1,86 @@
+# -*- python -*-
+#
+# $Id: im_weakref.py,v 1.1 2011-06-08 15:50:07 wirawan Exp $
+#
+# wpylib.py.im_weakref
+# Created: 20110607
+# Wirawan Purwanto
+#
+# Advanced hack tools for python: weakref proxy class for instance-method.
+#
+
+"""
+wpylib.py.im_weakref
+
+Complement of weakref's weak reference for an instance method
+(whether bound or unbound).
+
+Original-source: Linux Screen Reader project
+Copied-from: http://mindtrove.info/python-weak-references/
+Date: 20110607
+"""
+
+import weakref, new
+
+class im_ref(object):
+  '''
+  Our own proxy object which enables weak references to bound and unbound
+  methods and arbitrary callables. Pulls information about the function,
+  class, and instance out of a bound method. Stores a weak reference to the
+  instance to support garbage collection.
+
+  @organization: IBM Corporation
+  @copyright: Copyright (c) 2005, 2006 IBM Corporation
+  @license: The BSD License
+  '''
+  def __init__(self, cb):
+    try:
+      try:
+        self.inst = weakref.ref(cb.im_self)
+      except TypeError:
+        self.inst = None
+      self.func = cb.im_func
+      self.klass = cb.im_class
+    except AttributeError:
+      self.inst = None
+      self.func = cb.im_func
+      self.klass = None
+
+  def __call__(self, *args, **kwargs):
+    '''
+    Proxy for a call to the weak referenced object. Take arbitrary params to
+    pass to the callable.
+
+    @raise ReferenceError: When the weak reference refers to a dead object
+    '''
+    if self.inst is not None and self.inst() is None:
+      raise ReferenceError
+    elif self.inst is not None:
+      # build a new instance method with a strong reference to the instance
+      mtd = new.instancemethod(self.func, self.inst(), self.klass)
+    else:
+      # not a bound method, just return the func
+      mtd = self.func
+    # invoke the callable and return the result
+    return mtd(*args, **kwargs)
+
+  def __eq__(self, other):
+    '''
+    Compare the held function and instance with that held by another proxy.
+
+    @param other: Another proxy object
+    @type other: L{Proxy}
+    @return: Whether this func/inst pair is equal to the one in the other
+    proxy object or not
+    @rtype: boolean
+    '''
+    try:
+      return self.func == other.func and self.inst() == other.inst()
+    except Exception:
+      return False
+
+  def __ne__(self, other):
+    '''
+    Inverse of __eq__.
+    '''
+    return not self.__eq__(other)