file system walk which can go very deep ( no recursion limit )

walk_chdir.py

#!/usr/local/bin/python3

import os
import logging

logger = logging.getLogger(__name__)

def commonpath(d1, d2):
    " returns the length of longest common leading component "

    i = 0
    m = min(len(d1), len(d2))

    while i < m:
        if d1[i] != d2[i]:
            break
        i += 1
    return i


def to_list(path):

    path = os.path.normpath(path)
    if path == os.path.sep:
        return ['']
    return path.split(os.path.sep)


def to_string(path):

    if path == ['']:
        return os.path.sep
    return os.path.sep.join(path)


def chdir(cwd, new_dir):
    " chdir from cwd new new_dir "

    common_len = commonpath(cwd, new_dir)

    for _ in range(len(cwd) - common_len):
        os.chdir('..')

    cwd = cwd[:common_len]

    for d in new_dir[common_len:]:
        try:
            os.chdir(d)
        except FileNotFoundError as e:
            logger.error("%s: '%s'", e.strerror, os.path.join(to_string(cwd), e.filename))
            break

        cwd.append(d)

    return cwd


def walk_chdir(top):

    top = to_list(os.path.realpath(top))

    stack = [top]
    keep_cwd = os.getcwd()
    cwd = keep_cwd.split(os.path.sep)

    while stack:

        new_dir = stack.pop()
        cwd = chdir(cwd, new_dir)

        if cwd == new_dir:
            scandir_it = os.scandir()
            for entry in scandir_it:
                yield (to_string(cwd), entry)
                if entry.is_dir(follow_symlinks=False):
                    stack.append(cwd + [entry.name])

    os.chdir(keep_cwd)


top = '/var'
for (cwd, entry) in walk_chdir(top):
    if entry.is_symlink():
        print(os.path.normpath(os.path.join(cwd, entry)))