python - 如何正确计算基尼指数？

Question

该函数接收一个列表并计算一个基尼指数。基尼指数的计算方法是用 1 减去每个类别的概率平方和。

Input
 - values: a list of labels.
Output
 - impurity: gini index of the list.

def gini(values):
    height, area = 0, 0
    for value in values:
        height += value
        area += height - value / 2.
    fair_area = height * len(values) / 2.
    impurity = (fair_area - area) / fair_area
    return impurity

impurity should be 0.4082 for gini([0,0,0,0,0,1,1]) (now its 0.7142)
and 0.5 for gini([0,0,1,1]) (this works)

如何根据最终结果正确计算？