将列表理解与 if、else 和 for 循环结合使用，同时仅保留满足条件的列表项

Question

我使用列表理解来仅加载满足特定条件的文件夹中的图像。 在同样的操作中，我还想跟踪那些不符合条件的。这就是我遇到麻烦的地方。

如果

if

和

else

条件位于开头，则每次迭代都会产生一个结果元素。被

else

捕获的项目将被

None

替换，而不是从结果列表中排除。

我不知道如何添加

else

条件，以便可以对

else

捕获的项目执行操作，而不将它们包含在结果列表中。

这是代码的简化和通用版本：

exclude_imgs = [1, 3]
final = [
    n
    for ix, n in enumerate(sorted(["img1", "img4", "img3", "img5", "img2"]))
    if ix + 1 not in exclude_imgs
]

[ins] In [4]: final
Out[4]: ['img2', 'img4', 'img5']

添加

else

条件来存储排除的图像：

exclude_imgs = [1, 3]
excluded = []
final = [
    n if ix + 1 not in exclude_imgs else excluded.append(n)
    for ix, n in enumerate(sorted(["img1", "img4", "img3", "img5", "img2"]))
]

[ins] In [6]: final
Out[6]: [None, 'img2', None, 'img4', 'img5']

[ins] In [7]: excluded
Out[7]: ['img1', 'img3']

我该如何写才能得到如下结果：

final: ['img2', 'img4', 'img5']
excluded: ['img1', 'img3']

？

Answer 1

考虑根本不使用列表理解，正是因为您想要创建两个列表，而不仅仅是一个。

exclude_imgs = [1, 3]
excluded = []
final = []

for ix, n in enumerate(sorted(["img1", "img4", "img3", "img5", "img2"]), start=1):
    (excluded if ix in excluded_imgs else final).append(n)

Answer 2

exclude_imgs = [1, 3]

# convert all element of exclude_imgs into string
exclude_imgs = [str(x) for x in exclude_imgs]

# declare the list of images into a variable so that it is easy to call later. No need to sort
img_lst = ["img1", "img4", "img3", "img5", "img2"]

excluded = []
final = []

# No need to sort
for x in img_lst:

    # This condition checks if any of exclude_imgs is present in the image.
    if any(y in x for y in exclude_imgs):

        excluded.append(x)
    else:
        final.append(x)

print(excluded)     # Output: ['img1', 'img3']

print(final)        # Output: ['img4', 'img5', 'img2']