With new-style classes, is is no longer possible to override slots

(special '__' methods) on an instance-by instance basis. Changed the
handling of the length so that the __len__ method looks for a __len__
dictionary key. It would be better not to use a __len__ attribute name
for the BTree length object, but such a change would be problematic
for old instances.

lib/python/Products/PluginIndexes/common/UnIndex.py

@@ -13,7 +13,7 @@
 
 """Simple column indices"""
 
-__version__='$Revision: 1.20 $'[11:-2]
+__version__='$Revision: 1.21 $'[11:-2]
 
 import sys
 from cgi import escape
@@ -21,8 +21,6 @@ from types import StringType, ListType, IntType, TupleType
 
 from Globals import Persistent
 from Acquisition import Implicit
-import BTree
-import IOBTree
 from zLOG import LOG, ERROR
 
 from BTrees.OOBTree import OOBTree, OOSet
@@ -95,11 +93,27 @@ class UnIndex(Persistent, Implicit, SimpleItem):
         except:
             self.indexed_attrs = [ self.id ] 
         
+        # It was a mistake to use a __len__ attribute here, but it's not
+        # worth changing at this point, as there is old data with this
+        # attribute name. :( See __len__ method docstring
+        self.__len__ = BTrees.Length.Length() 
 
-        self.__len__=BTrees.Length.Length() # see __len__ method docstring
         self.clear()
 
-    def getId(self): return self.id
+    def __len__(self):
+        """Return the number of objects indexed.
+        """
+
+        # The instance __len__ attr isn't effective because
+        # Python cached this method in a slot,
+        __len__ = self.__dict__.get('__len__')
+        if __len__ is not None:
+            return __len__() 
+        
+        return len(self._unindex)
+
+    def getId(self):
+        return self.id
 
     def clear(self):
         # inplace opportunistic conversion from old-style to new style BTrees
@@ -140,15 +154,6 @@ class UnIndex(Persistent, Implicit, SimpleItem):
     def __nonzero__(self):
         return not not self._unindex
 
-    def __len__(self):
-        """Return the number of objects indexed.
-
-        This method is only called for indexes which have "old" BTrees,
-        and the *only* reason that UnIndexes maintain a __len__ is for
-        the searching code in the catalog during sorting.
-        """
-        return len(self._unindex)
-
     def histogram(self):
         """Return a mapping which provides a histogram of the number of
         elements found at each point in the index."""

lib/python/Products/Transience/Transience.py

@@ -13,10 +13,10 @@
 """
 Transient Object Container Class ('timeslice'-based design).
 
-$Id: Transience.py,v 1.33 2003/11/18 13:17:08 tseaver Exp $
+$Id: Transience.py,v 1.34 2003/11/28 16:46:11 jim Exp $
 """
 
-__version__='$Revision: 1.33 $'[11:-2]
+__version__='$Revision: 1.34 $'[11:-2]
 
 import Globals
 from Globals import HTMLFile
@@ -427,8 +427,16 @@ class TransientObjectContainer(SimpleItem):
             # our "__len__" is the length of _index.
             # we need to maintain the length of the index structure separately
             # because getting the length of a BTree is very expensive.
-            try: self.__len__.set(0)
-            except AttributeError: self.__len__ = self.getLen = Length()
+            # Note that it is a mistake to use the __len__ attr this way,
+            # because length methods are cached in C slots and out instance
+            # attr won't be used for len(foo) in new-style classes.
+            # See the __len__ method below. I (Jim) am not changing this now
+            # on account of ols instances. With some effort, we could fix this,
+            # bit I'm not up for it now.
+            try:
+                self.__len__.set(0)
+            except AttributeError:
+                self.__len__ = Length()
 
             # set up last_timeslice and deindex_next integer pointers
             # we set them to the current timeslice as it's the only sane
@@ -438,6 +446,12 @@ class TransientObjectContainer(SimpleItem):
         finally:
             self.lock.release()
 
+    def __len__(self):
+        return self.__dict__['__len__']()
+
+    def getLen(self):
+        return self.__len__
+
     def _getCurrentBucket(self):
         """
         Do housekeeping if necessary, then return the 'current' bucket.

lib/python/Products/ZCatalog/Catalog.py

@@ -76,7 +76,13 @@ class Catalog(Persistent, Acquisition.Implicit, ExtensionClass.Base):
         # object unique identifier to the rid, and self.paths is a
         # mapping of the rid to the unique identifier.
 
-        self.__len__=BTrees.Length.Length()
+        # Note that it was unfortunate to use __len__ as the attribute
+        # name here. New-style classes cache slot methods in C slot
+        # pointers. The result is that instances can't override slots.
+        # This is not easy to change on account of old objects with
+        # __len__ attr.
+
+        self.__len__ = BTrees.Length.Length()
         self.clear()
 
         if brains is not None:
@@ -84,6 +90,14 @@ class Catalog(Persistent, Acquisition.Implicit, ExtensionClass.Base):
 
         self.updateBrains()
 
+    def __len__(self):
+        try:
+            return self.__dict__['__len__']()
+        except KeyError:
+            # Fallback for *really* old catalogs that don't have
+            # Length objects. 
+            return len(self.data)
+
     def clear(self):
         """ clear catalog """
 
@@ -122,11 +136,6 @@ class Catalog(Persistent, Acquisition.Implicit, ExtensionClass.Base):
             if hasattr(index, '__of__'): index=index.__of__(self)
             index._convertBTrees(threshold)
 
-    def __len__(self):
-        # NOTE, this is never called for new catalogs, since
-        # each instance overrides this.
-        return len(self.data)
-
     def updateBrains(self):
         self.useBrains(self._v_brains)
 

lib/python/SearchIndex/UnIndex.py

@@ -13,7 +13,7 @@
 
 """Simple column indices"""
 
-__version__='$Revision: 1.33 $'[11:-2]
+__version__='$Revision: 1.34 $'[11:-2]
 
 from Globals import Persistent
 from Acquisition import Implicit
@@ -75,9 +75,22 @@ class UnIndex(Persistent, Implicit):
         self.ignore_ex=ignore_ex        # currently unimplimented
         self.call_methods=call_methods
 
-        self.__len__=BTrees.Length.Length() # see __len__ method docstring
+        # Note that it was unfortunate to use __len__ as the attribute
+        # name here. New-style classes cache slot methods in C slot
+        # pointers. The result is that instances can't override slots.
+        # This is not easy to change on account of old objects with
+        # __len__ attr.
+
+        self.__len__=BTrees.Length.Length()
         self.clear()
 
+    def __len__(self):
+        try:
+            return self.__dict__['__len__']()
+        except KeyError:
+            # Fallback for really old indexes
+            return len(self._unindex)
+
     def clear(self):
         # inplace opportunistic conversion from old-style to new style BTrees
         try: self.__len__.set(0)
@@ -117,15 +130,6 @@ class UnIndex(Persistent, Implicit):
     def __nonzero__(self):
         return not not self._unindex
 
-    def __len__(self):
-        """Return the number of objects indexed.
-
-        This method is only called for indexes which have "old" BTrees,
-        and the *only* reason that UnIndexes maintain a __len__ is for
-        the searching code in the catalog during sorting.
-        """
-        return len(self._unindex)
-
     def histogram(self):
         """Return a mapping which provides a histogram of the number of
         elements found at each point in the index."""