Index: tools/opt-viewer/optrecord.py
===================================================================
--- tools/opt-viewer/optrecord.py
+++ tools/opt-viewer/optrecord.py
@@ -146,7 +146,7 @@
             del mapping['DebugLoc']
 
         assert(len(mapping) == 1)
-        (key, value) = mapping.items()[0]
+        (key, value) = list(mapping.items())[0]
 
         if key == 'Caller' or key == 'Callee':
             value = cgi.escape(demangle(value))