This change stops sleekxmpp from spending huge amounts of time unnecessarily computing logging data that may never be used. This is a HUGE performance improvement; in some of my test runs, unnecessary string creation was accounting for > 60% of all CPU time.

Note that using % in a string will _always_ perform the sting substitutions, because the strings are constructed before the function is called. So log.debug('%s' % expensiveoperation()) will take about the same CPU time whether or not the logging level is DEBUG or INFO. if you use , no substitutions are performed unless the string is actually logged

sleekxmpp/features/feature_mechanisms/mechanisms.py

@@ -123,7 +123,7 @@ class feature_mechanisms(base_plugin):
 
     def _handle_fail(self, stanza):
         """SASL authentication failed. Disconnect and shutdown."""
-        log.info("Authentication failed: %s" % stanza['condition'])
+        log.info("Authentication failed: %s" , stanza['condition'])
         self.xmpp.event("failed_auth", stanza, direct=True)
         self.xmpp.disconnect()
         return True