append 如何与 python 中的 for 循环一起使用

Question

t=int(input())
#c=[i for i in range(t)]
for i in range(t):

    n=int(input())
    a = list(map(int,input().strip().split()))
    b = list()

    for i in range(n):
        if(a[i]==1):
            b.append(i)


    print(b)

when list a is (1 0 1), list b is( 0,2 ) when list a is 1 0 0 1, list b is 0,3 In fact, I suppose the output of list b is ( 1,1) instead of 0, 2 since its definition is to add the obj into list Please tell me if there's something I miss or get wrong, thanks

Answer 1

You append i , which is the index, and not a[i] which is the value from a .

so b is essentially a list containing all indexes of elements in a that are equal 1