vnpy的回测报告中好像没有按年统计的每年盈亏金额，
我想在脚本回测中实现，

engine = BacktestingEngine()
engine.set_parameters(
    vt_symbol = "000001.SZSE",
    interval ="d",
    start = datetime(2018,3,23),
    end = datetime(2018,4,23),
    rate = 0,
    slippage = 0,
    size = 10,
    pricetick = 0.2,
    capital = 1_000_000,
    )

engine.add_strategy(BollChannelStrategy,{})
engine.load_data()
engine.run_backtesting()
df = engine.calculate_result()
engine.calculate_statistics()
engine.show_chart()

要怎么弄呢？