def get_middle_percent(self, percent):
        """Return the left and right values of the middle %
        
        Parameters:
        1. percent: the middle percent
        """
        
        w = []
        for chrom in self.get_chroms():
            w += self[chrom][1]
        w.sort()
        wlen= len(w)
        left = int(((100-percent)/200.0)*(1-wlen))
        return w[left], w[-1*left]
dataset/ETHPy150Open taoliu/taolib/Assoc/inout.py/Wig.get_middle_percent/swapped operands of `-`