奇葩問題ValueError: math domain error，已解決！！！

　　在實現決策樹的ID3算法時，編寫了計算信息熵的函數，運行后遇到了如下的問題：

 

 　　對應處的代碼為：

    @staticmethod
    def calc_ent(datasets):
        data_length = len(datasets)
        label_count = {}
        for i in range(data_length):
            label = datasets[i][-1]
            if label not in label_count:
                label_count[label] = 0
            else:
                label_count[label] += 1
        ent = -sum([(p / data_length) * log(p / data_length, 2) for p in label_count.values()])
        return ent

　　經過不斷地試錯與百度，最后解決了該問題，竟然是把else:去掉：

    @staticmethod
    def calc_ent(datasets):
        data_length = len(datasets)
        label_count = {}
        for i in range(data_length):
            label = datasets[i][-1]
            if label not in label_count:
                label_count[label] = 0
            label_count[label] += 1
        ent = -sum([(p / data_length) * log(p / data_length, 2) for p in label_count.values()])
        return ent

　　運行成功：

 

 　　根據報錯提示，原因應該是數學域錯誤，不知道為什么刪掉else:就成功了......