#NEWLINE# def __setitem__( self , n , obj ) : #NEWLINE# #INDENT# if obj . wasset : #NEWLINE# #INDENT# raise RuntimeError ( ( 'setitem should only be called once, setting %r to %r' % ( n , obj ) ) ) #NEWLINE# #UNINDENT# else : #NEWLINE# #INDENT# self . wasset = 1 #NEWLINE# #UNINDENT# self . callback ( obj )