diff -u a/urllib.py b/urllib.py
--- a/urllib.py	2010-06-03 11:17:32.000000000 +0400
+++ b/urllib.py	2010-06-03 11:20:04.000000000 +0400
@@ -1375,7 +1375,10 @@
                         continue
 
                 base = ip2num(m.group(1))
-                mask = int(m.group(2)[1:])
+                if m.group(2) is not None:
+                    mask = int(m.group(2)[1:])
+                else:
+                    mask = 8 * (m.group(1).count('.') + 1)
                 mask = 32 - mask
 
                 if (hostIP >> mask) == (base >> mask):