收益率方差和标准差计算

import math
def solve(probabilities, returns):
    expected = sum(p * r for p, r in zip(probabilities, returns))
    variance = sum(p * (r - expected) ** 2 for p, r in zip(probabilities, returns))
    std_dev = math.sqrt(variance)
    return {"方差": round(variance, 6), "标准差": round(std_dev, 4)}