mercurial/revset.py

--- a/mercurial/revset.py	Wed Mar 19 17:53:45 2014 -0700
+++ b/mercurial/revset.py	Thu Mar 20 18:55:28 2014 -0700
@@ -2464,6 +2464,9 @@
         self._ascending = ascending
         self._genlist = None
 
+    def __len__(self):
+        return len(self._list)
+
     @util.propertycache
     def _list(self):
         if not self._genlist: