Python append 多元素

Question

I have a list(T) of 6500 images(arrays) that I am using for image classification, and I would like to see how increasing the data affects the accuracy.

So, starting from n=2000 images, I am thinking of having a loop that will add 500(n+=500) images at each iteration till it reaches 6500 and therefore compare the accuracy between 2000, 2500, 3000, ... 6500. I have simplified the problem below by having a list of 20 elements.

lst = [1,2,3,4,5,6,7,8,9,0,1,2,3,4,5,6,7,8,9,0]

My second list ( slist ) contains the first 9 elements of the first list ( lst ).

I am trying to add 2 values to slist at each iteration, starting from lst[9:] . I know rather than using append , extend should be used to add multiple values at once. However, I couldn't find a way to do it.

In the following code, one element is added to slist (from lst ) at each loop.

lst = [1,2,3,4,5,6,7,8,9,0,1,2,3,4,5,6,7,8,9,0]
slist = lst[:9]
for i in lst[9:]:
    slist.append(i)

How can I add 2 or 3 elements simultaneously at each loop? An example output would be:

[1,2,3,4,5,6,7,8,9,0,1]

[1,2,3,4,5,6,7,8,9,0,1,2,3]

[1,2,3,4,5,6,7,8,9,0,1,2,3,4,5]

Answer 1

You could try using extend :

l = [1,2,3,4,5,6,7,8,9,0,1,2,3,4,5,6,7,8,9,0]
slist = l[:9]
for i in l[9:][::2]:
    if i == l[9]:
        slist.extend(l[9+i: 9+i+1])
    else:
        slist.extend(l[9+i-1: 9+i+1])
    print(slist)

Output:

[1, 2, 3, 4, 5, 6, 7, 8, 9, 0]
[1, 2, 3, 4, 5, 6, 7, 8, 9, 0, 1, 2]
[1, 2, 3, 4, 5, 6, 7, 8, 9, 0, 1, 2, 3, 4]
[1, 2, 3, 4, 5, 6, 7, 8, 9, 0, 1, 2, 3, 4, 5, 6]
[1, 2, 3, 4, 5, 6, 7, 8, 9, 0, 1, 2, 3, 4, 5, 6, 7, 8]
[1, 2, 3, 4, 5, 6, 7, 8, 9, 0, 1, 2, 3, 4, 5, 6, 7, 8, 0]

Answer 2

lst=[1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,
  16,17,18,19,20]

iter = 9
while True:
    print(lst[:iter])
    iter+=2
    if len(lst) <= iter:
        print(lst[:iter])
        break

Answer 3

This code does the job

lst=[1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,
  16,17,18,19,21]

slist= lst[:9]
s,f=0,2
while True:
    slist.extend(lst[9:][s:f])
    print(slist)
    s+=2
    f+=2
    if len(slist) >= len(lst):
        break

It prints out:

[1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11]
[1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13]
[1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15]
[1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17]
[1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19]
[1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21]