Index: src/org/python/core/PyString.java
===================================================================
--- src/org/python/core/PyString.java	(revision 3222)
+++ src/org/python/core/PyString.java	(working copy)
@@ -2795,6 +2795,11 @@
         if (s != null)
             sval = s.toString();
         try {
+            // Double.valueOf allows format specifier ("d" or "f") at the end
+            String lowSval = sval.toLowerCase();
+            if (lowSval.endsWith("d") || lowSval.endsWith("f")) {
+                throw new NumberFormatException("format specifiers not allowed");
+            }
             return Double.valueOf(sval).doubleValue();
         }
         catch (NumberFormatException exc) {