#NEWLINE# def __setitem__( self , key , value ) : #NEWLINE# #INDENT# if ( value in self . _reverse ) : #NEWLINE# #INDENT# raise KeyError ( ( "Can't have key %r on both sides!" % key ) ) #NEWLINE# #UNINDENT# dict . __setitem__ ( self , key , value ) #NEWLINE# self . _reverse [ value ] = key