求请教一句代码，关于for循环的

Question

average_mae_history = [np.mean([x[i] for x in all_mae_histories]) for i in range(num_epoachs)]
这句看不懂

Answer 1

就是嵌套列表生成式了,
比如一个可迭代对象arr=[1,2,3]
通过表达式[i+1 for i in arr]就能产生一个[2,3,4]的列表
这里相当于：

average_mae_history = []
for i in range(num_epoachs):
    arr = []
    for x in all_mae_histories:
        arr.append(x[i])
    average_mae_history.append(np.mean(arr))