如何重用pyalgotrade的实例策略类

from pyalgotrade import strategy

class MyStrategy(strategy.Strategy):
    def __init__(self, feed, instrument):
        super(MyStrategy, self).__init__(feed)
        self.__instrument = instrument
        self.__sma = ma.SMA(feed[instrument].getCloseDataSeries(), 15)

def onBars(self, bars):
    if self.__sma[-1] is None:
        return

    bar = bars[self.__instrument]
    if self.__sma[-1] > bar.getPrice():
        self.marketOrder(self.__instrument, 1)
    elif self.__sma[-1] < bar.getPrice():
        self.marketOrder(self.__instrument, -1)

from pyalgotrade import bar
from pyalgotrade import plotter
from pyalgotrade import strategy
from pyalgotrade.barfeed import yahoofeed

# 创建回测引擎对象
feed = yahoofeed.Feed()
feed.addBarsFromCSV("spy", "spy.csv")

# 实例化策略类并添加到引擎中
myStrategy = MyStrategy(feed, "spy")

# 运行回测引擎
myStrategy.run()