#NEWLINE# def postorder( self , f ) : #NEWLINE# #INDENT# 'Postorder traversal, applying a function to each operator.  The\n        function returns an iterator' #NEWLINE# for c in self . children ( ) : #NEWLINE# #INDENT# for x in c . postorder ( f ) : #NEWLINE# #INDENT# ( yield x ) #NEWLINE# #UNINDENT# #UNINDENT# for x in f ( self ) : #NEWLINE# #INDENT# ( yield x )