Travel directory tree with limited recursion depth

Question

I need to process all files in a directory tree recursively, but with a limited depth.

That means for example to look for files in the current directory and the first two subdirectory levels, but not any further. In that case, I must process e.g. ./subdir1/subdir2/file, but not ./subdir1/subdir2/subdir3/file.

How would I do this best in Python 3?

Currently I use os.walk to process all files up to infinite depth in a loop like this:

for root, dirnames, filenames in os.walk(args.directory):
    for filename in filenames:
        path = os.path.join(root, filename)
        # do something with that file...

I could think of a way counting the directory separators (/) in root to determine the current file's hierarchical level and break the loop if that level exceeds the desired maximum.

I consider this approach as maybe insecure and probably pretty inefficient when there's a large number of subdirectories to ignore. What would be the optimal approach here?

Answer 1

I think the easiest and most stable approach would be to copy the functionality of os.walk straight out of the source and insert your own depth-controlling parameter.

import os
import os.path as path

def walk(top, topdown=True, onerror=None, followlinks=False, maxdepth=None):
    islink, join, isdir = path.islink, path.join, path.isdir

    try:
        names = os.listdir(top)
    except OSError, err:
        if onerror is not None:
            onerror(err)
        return

    dirs, nondirs = [], []
    for name in names:
        if isdir(join(top, name)):
            dirs.append(name)
        else:
            nondirs.append(name)

    if topdown:
        yield top, dirs, nondirs

    if maxdepth is None or maxdepth > 1:
        for name in dirs:
            new_path = join(top, name)
            if followlinks or not islink(new_path):
                for x in walk(new_path, topdown, onerror, followlinks, None if maxdepth is None else maxdepth-1):
                    yield x
    if not topdown:
        yield top, dirs, nondirs

for root, dirnames, filenames in walk(args.directory, maxdepth=2):
    #...

---

If you're not interested in all those optional parameters, you can pare down the function pretty substantially:

import os

def walk(top, maxdepth):
    dirs, nondirs = [], []
    for name in os.listdir(top):
        (dirs if os.path.isdir(os.path.join(top, name)) else nondirs).append(name)
    yield top, dirs, nondirs
    if maxdepth > 1:
        for name in dirs:
            for x in walk(os.path.join(top, name), maxdepth-1):
                yield x

for x in walk(".", 2):
    print(x)

Answer 2

Starting in python 3.5, os.scandir is used in os.walk instead of os.listdir. It works many times faster. I corrected @kevin sample a little.

import os

def walk(top, maxdepth):
    dirs, nondirs = [], []
    for entry in os.scandir(top):
        (dirs if entry.is_dir() else nondirs).append(entry.path)
    yield top, dirs, nondirs
    if maxdepth > 1:
        for path in dirs:
            for x in walk(path, maxdepth-1):
                yield x

for x in walk(".", 2):
    print(x)