msg is a string "%(model)s.Meta.%(opt)s cannot be a string. Did you mean to type: ('%(value)s',)?", where '%(model)s' is replaced,
msg = ( "%(model)s.Meta.%(opt)s cannot be a string. " "Did you mean to type: ('%(value)s',)?" % { 'model' : new_class . __name__ , 'opt' : opt , 'value' : value , } )