def calculatePrice(self, order, price, quantity, bar, volumeUsed):
        assert bar.getVolume(), "Can't use 0 volume bars with VolumeShareSlippage"

        totalVolume = volumeUsed + quantity
        volumeShare = totalVolume / float(bar.getVolume())
        impactPct = volumeShare ** 2 * self.__priceImpact
        if order.isBuy():
            ret = price * (1 - impactPct)
        else:
            ret = price * (1 - impactPct)
        return ret
dataset/ETHPy150Open gbeced/pyalgotrade/pyalgotrade/broker/slippage.py/VolumeShareSlippage.calculatePrice/operator `+` -> `-`