Python move "met conditional value" outside of loop

Question

This may be confusing.

rootdir= C:\User\Desktop\File
file = 'file.txt'

mainLocNum = str(list(rootdir)).count(r'\\')
mainFolder=os.listdir(rootdir)

with open(file,'w') as f:

    for dir, subdirs, files in os.walk(rootdir):
        currentDirLevel=str(list(dir)).count(r'\\')
        for allFolders in subdirs:
            if (currentDirLevel - mainLocNum) == 0:
                parentFolders=allFolders
                f.write(str(parentFolders))
                PLACEHOLDER
            elif (currentDirLevel - mainLocNum) == 1:
                subFolders=allFolders
                f.write(str(allFolders)     <----- write this in PLACEHOLDER

I want to write the second write statement into the PLACEHOLDER line only if the elif condition is met. If I don't write the second write statement in the PLACEHOLDER position, the second write statement in the second conditional is written at the very bottom of the text file; however I want to write the second conditional's write statement (only if it is met) in the PLACEHOLDER position, which is in between each of the first write iterations.

I've been trying different nesting methods, but I am lacking in fundamental loop construction logic.

Any help is appreciated, thanks!

EDIT:

I am looping through a main directory, and I am writing all of the parent folders into the text file. I want to write in between each parent folder its subfolders: i.e if the parent folder contains more folders, to write those folders in between each parent folder; and if the parent folder does not contain any more folders, to skip to the next parent folder etc. I am using the if (currentDirLevel - mainLocNum)==(number) to know how many directories it is stepping into and to perform a different write function for each step.

I am trying to write the names of the folders in certain formats depending on whether they are level 1 sub-directories, level 2 sub-directories etc...

What I want:

ParentFolder1
    SubFolder1
    Subfolder2
        SubSubFolder1
    SubFolder3
ParentFolder2
    SubFolder1
ParentFolder3
ParentFolder4
    SubFolder1
        SubSubFolder1
            SubSubSubFolder1
        SubSubFolder2
    SubFolder2
ParentFolder5
    SubFolder1

What I am getting

ParentFolder1
ParentFolder2
ParentFolder3
ParentFolder4
ParentFolder5
SubFolder1
SubFolder2
SubFolder3
SubFolder1
SubFolder1
SubFolder2
SubFolder1
SubSubFolder1
SubSubFolder1
SubSubFolder2
SubSubSubFolder1

Please don't focus on the os.walk or iterating through the directories. I have a lot of code written already, and I want the main focus to answer my question about running a conditional loop and placing the value within that loop into a write function inside another loop.

I would prefer restructuring this loop logic rather than starting over with the whole os.walk for loop.

Thanks again

Answer 1

I'm not quite sure what you mean by the term "conditional loop", but what you're trying to achieve is easily done using a small recursive function based on os.listdir. You could do this using os.walk, but I often find it simpler (and more efficient) to call os.listdir explicitly (os.walk calls os.listdir internally), especially when you don't need separate lists of directories and plain files.

import os

tab = 4 * ' '

def writedirs(fhandle, path, depth=0):
    ''' Recursively walk the directory tree starting at path,
        writing all directory names to open file handle fhandle.
        Nodes are traversed depth-first, top-down, and names
        are indented proportional to their depth.
    '''
    data = os.listdir(path)
    # Names returned by listdir are in file system order;
    # If you want them sorted alphabetically, call
    # data.sort()
    # or
    # data.sort(key=str.lower)
    # for case-insensitive sorting.

    indent = depth * tab
    depth += 1
    for filename in data:
        fullpath = os.path.join(path, filename)
        if os.path.isdir(fullpath):
            fhandle.write(indent + filename + '\n')
            writedirs(fhandle, fullpath, depth)

#Test
rootdir = 'testfolder'
outname = 'file.txt'
with open(outname, 'w') as fhandle:
    writedirs(fhandle, rootdir)

contents of 'file.txt'

ParentFolder1
    SubFolder1
    Subfolder2
        SubSubFolder1
    SubFolder3
ParentFolder2
    SubFolder1
ParentFolder3
ParentFolder4
    SubFolder1
        SubSubFolder1
            SubSubSubFolder1
        SubSubFolder2
    SubFolder2
ParentFolder5
    SubFolder1

It's generally better to avoid recursion in Python, when practical: the Python interpreter cannot perform tail call elimination, and it imposes a maximum recursion depth. However, when dealing with recursive data structures (like file trees) it's natural to use a recursive algorithm.

---

FWIW, the code below iteratively performs the inverse operation of the code above; I used it to build the directory tree from the indented list of directory names given in the question.

import os

data = '''
ParentFolder1
    SubFolder1
    Subfolder2
        SubSubFolder1
    SubFolder3
ParentFolder2
    SubFolder1
ParentFolder3
ParentFolder4
    SubFolder1
        SubSubFolder1
            SubSubSubFolder1
        SubSubFolder2
    SubFolder2
ParentFolder5
    SubFolder1
'''[1:]

def show(seq):
    for row in seq:
        print(row)
    print()

def stripcount(s):
    z = s.lstrip(' ')
    count = len(s) - len(z)
    return z, count

joinpath = os.path.join

def make_dir_tree(dir_tree, root=''):
    ''' Create a directory tree in root from dir_tree,
        which is a list of indented directory names.
    '''
    dir_tree = [stripcount(s) for s in dir_tree]
    #show(dir_tree)

    stack = [root]
    depth = -1
    for dname, count in dir_tree:
        if count > depth:
            depth = count
            stack.append(dname)
        elif count < depth:
            depth = count
            stack.pop()
            stack[-1] = dname
        else:
            stack[-1] = dname

        pathname = joinpath(*stack)
        print(pathname)
        os.mkdir(pathname)


dir_tree = data.splitlines()
show(dir_tree)
make_dir_tree(dir_tree, 'testfolder')