Python递归追加列表函数 [英] Python recursively appending list function

问题描述

递归函数有问题，本应相对简单，但似乎无法正确执行.

Having issues with a recursive function that should be relatively simple to do, but can`t seem to get right.

我有一个文件夹结构，其中的文件夹可以包含其他文件夹、图像或文件.每个文件夹都有关联的权限.我想让我的函数递归地构建一个与每个文件夹关联的权限列表.

I have a folder structure with folders that can contain other folders, images or files. Associated with each folder there are permissions. I want to have my function recursively build a list of the permissions that are associated with each folder.

我有一个函数 has_read_permission(request) 如果文件夹有权限则返回 True，否则返回 False

I have a function has_read_permission(request) that returns True if the folder has permissions and False if not

我已经构建了一个这样的函数:

I have built a function like so:

def get_child_perms(self, folder, request, perm_list):
        # Folder contains other folders
        if folder.get_children():
            # For every sub-folder
            for subfolder in folder.get_children():
                return perm_list.append(self.get_child_perms(subfolder, request, perm_list))
        else:
            # If folder doesn't have sub-folders containing folders
            return [folder.has_read_permission(request)]

我一直没有

给定的文件夹如下:

Folder (allowed) - Wont check this one
|_First Folder (allowed)
| |_First sub Folder (restricted)
| | |_File
| | |_File
| | |_Image
| |__Second Sub Folder (allowed)
|_Second Folder (allowed)

然后运行 ​​get_child_perms() 将返回[真，假，真，真]甚至[真，[假，真]，真]

Then running get_child_perms() would return [True,False,True,True] or even [True, [False, True], True]

编辑

忽略编辑 -> 询问其他问题 Python 递归函数缺失结果

Disregard edit -> asked other question Python Recursive function missing results

变身了，

def get_child_perms(self, folder, request, perm_list):
        if folder.get_children():
            for subfolder in folder.get_children():
                perm_list.append(self.get_child_perms(subfolder, request, perm_list))
            return perm_list
        else:
            return [folder.has_read_permission(request)]

得到:

[[True], [...], [True], [...], [...], [True], [True], [True], [True], [True], [True], [True], [True], [...], [True], [...]]

 Admin
 -Folder 1
   - Files
 -Folder 2
   - Files
 -Folder 3
   - Files 
 -Folder 4
   - SubFolder 1
      -SubSubFolder 1
         - Files
      - Files
   - SubFolder 2
      - SubSubFolder 2
           - Files
      - Files
 -Folder 5
   - SubFolder 3
       - Files
   - SubFolder 4
       - Files
   - SubFolder 5
       -Files
   - Files
 -Folder 6
   - Files
 -Folder 7
   - SubFoler 6
       - Files
   - Files
 -Folder 8
   - Files

推荐答案

正如所指出的 append 是一个 inplace 操作，它返回 None，你可以完全避免使用 append通过返回一个列表组合:

As pointed out append is an inplace operation that returns None, you can avoid using append at all by returning a list comp:

def get_child_perms(self, folder, request, perm_list):
    # Folder contains other folders
    children =  folder.get_children()
    if children:
        # For every sub-folder
        return [self.get_child_perms(subfolder, request, perm_list)
                for subfolder in children]
    return [folder.has_read_permission(request)]

你也不需要 else 因为你只能从函数中返回一次.

You don't need an else either as you can only return once from the function.

这篇关于Python递归追加列表函数的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！