大家帮帮忙，急啊，……

import numpy as np
a = [4, 5, 6] #假设给定的三个数4， 5，6
print('均值：', np.mean(a))
print('方差：', np.var(a))
print('标准差：', np.sqrt(np.var(a)))

nums = 3.5, 4.2, 2.8
u = sum(nums) / len(nums)
o2 = sum([(_ - u) ** 2 for _ in nums]) / len(nums)
o = o2 ** 0.5
print(f'均值：{u:.2f}方差：{o2:.2f}标准差：{o:.2f}')