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/stanza/rootstanza.py

@@ -80,8 +80,7 @@ class RootStanza(StanzaBase):
             self['error']['type'] = 'cancel'
             self.send()
             # log the error
-            log.exception('Error handling {%s}%s stanza' %
-                          (self.namespace, self.name))
+            log.exception('Error handling {%s}%s stanza' ,  self.namespace, self.name)
             # Finally raise the exception to a global exception handler
             self.stream.exception(e)