【代码报错】big trade下单问题

老版本的trade复制到big trade里 这句话一直报错，请问要怎么修改

ranker_prediction = context.ranker_prediction[(

    context.ranker_prediction.date == data.current_dt.strftime('%Y-%m-%d'))&(context.ranker_prediction.score>=0.4)\]

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  AttributeError: 'StrategyContext' object has no attribute 'ranker_prediction'