#NEWLINE# def __iadd__( self , other ) : #NEWLINE# #INDENT# '\n        Combine the chart with another one\n        ' #NEWLINE# if ( not isinstance ( self , ChartBase ) ) : #NEWLINE# #INDENT# raise TypeError ( 'Only other charts can be added' ) #NEWLINE# #UNINDENT# self . _charts . append ( other ) #NEWLINE# return self