[Checkins] SVN: zc.sourcefactory/trunk/ - fixed another scalability bug caused by missing __nonzero__

[Benji York]

Log message for revision 85190:
  - fixed another scalability bug caused by missing __nonzero__
  - updating CHANGES.txt with previous release info
  

Changed:
  U   zc.sourcefactory/trunk/CHANGES.txt
  U   zc.sourcefactory/trunk/src/zc/sourcefactory/mapping.py
  U   zc.sourcefactory/trunk/src/zc/sourcefactory/mapping.txt

-=-
Modified: zc.sourcefactory/trunk/CHANGES.txt
===================================================================
--- zc.sourcefactory/trunk/CHANGES.txt	2008-04-09 15:15:12 UTC (rev 85189)
+++ zc.sourcefactory/trunk/CHANGES.txt	2008-04-09 15:23:12 UTC (rev 85190)
@@ -2,22 +2,37 @@
 Changes
 =======
 
-After 0.2.1
-===========
 
+0.3.2 (2008-04-09)
+==================
+
+    - Fixed scalability bug caused by missing __nonzero__ on ValueMappingSource
+
+
+0.3.1 (2008-02-12)
+==================
+
+    - Fixed scalability bug caused by missing __nonzero__ on BasicSourceFactory
+
+
+0.3.0 (??????????)
+==================
+
     - Added class-level defaults for attributes that are declared in the
       interfaces to not have the Zope 2 security machinery complain about
       them.
 
+
 0.2.1 - 2007-07-10
 ==================
 
     - Fixed a bug in the contextual token policy that was handling the
       resolution of values for a given token incorrectly.
 
-0.2 - 2007-07-10
-================
 
+0.2.0 - 2007-07-10
+==================
+
     - Added a contextual token policy interface that allows getToken and
       getValue to access the cotext for contextual sources.
 

Modified: zc.sourcefactory/trunk/src/zc/sourcefactory/mapping.py
===================================================================
--- zc.sourcefactory/trunk/src/zc/sourcefactory/mapping.py	2008-04-09 15:15:12 UTC (rev 85189)
+++ zc.sourcefactory/trunk/src/zc/sourcefactory/mapping.py	2008-04-09 15:23:12 UTC (rev 85190)
@@ -71,3 +71,8 @@
 
     def __len__(self):
         return len(self.base)
+
+    def __nonzero__(self):
+        for dummy in self.base:
+            return True
+        return False

Modified: zc.sourcefactory/trunk/src/zc/sourcefactory/mapping.txt
===================================================================
--- zc.sourcefactory/trunk/src/zc/sourcefactory/mapping.txt	2008-04-09 15:15:12 UTC (rev 85189)
+++ zc.sourcefactory/trunk/src/zc/sourcefactory/mapping.txt	2008-04-09 15:23:12 UTC (rev 85190)
@@ -43,3 +43,26 @@
   True
   >>> 1 in bound_source
   False
+
+
+Scaling
+-------
+
+Sometimes the number of items available through a source is very large.  So
+large that you only want to access them if absolutely neccesary.  One such
+occasion is with truth-testing a source.  By default Python will call
+__nonzero__ to get the boolean value of an object, but if that isn't available
+__len__ is called to see what it returns.  That might be very expensive, so we
+want to make sure it isn't called.
+
+  >>> class ExpensiveSource(object):
+  ...     def __len__(self):
+  ...         raise RuntimeError("oops, don't want to call __len__")
+  ...
+  ...     def __iter__(self):
+  ...         return iter(xrange(999999))
+
+  >>> expensive_source = ExpensiveSource()
+  >>> mapped_source = ValueMappingSource(expensive_source, map)
+  >>> bool(mapped_source)
+  True