Lib/os.py (part 5)

Source:

cpython 3.14 @ ab2d84fe1023/Lib/os.py ↗

This annotation covers directory traversal and file metadata. See module_os4_detail for os.open, os.read, os.write, os.close, and process management.

Map

Lines	Symbol	Role
1-80	os.scandir	Efficient directory listing with DirEntry
81-160	DirEntry	Cached file metadata from the OS
161-260	os.walk	Top-down or bottom-up directory traversal
261-360	os.stat_result	Named tuple for os.stat() output
361-500	os.environ	Mapping interface to environment variables

Reading

os.scandir and DirEntry

# CPython: Lib/os.py:1080 scandir
# (wraps Modules/posixmodule.c os_scandir_impl)

# DirEntry provides:
#   .name       — filename (not full path)
#   .path       — full path
#   .inode()    — inode number
#   .is_dir()   — True if this is a directory (follows symlinks by default)
#   .is_file()  — True if this is a regular file
#   .is_symlink() — True if this is a symbolic link
#   .stat()     — os.stat_result (cached)

os.scandir() returns a context manager (ScandirIterator) that yields DirEntry objects. The OS provides is_dir/is_file information "for free" on most platforms (via d_type on Linux, FindFileData.dwFileAttributes on Windows), avoiding extra stat calls.

os.walk

# CPython: Lib/os.py:340 walk
def walk(top, topdown=True, onerror=None, followlinks=False):
    """Directory tree generator.
    For each directory in the tree rooted at top, yields (dirpath, dirnames, filenames)."""
    with scandir(top) as scandir_it:
        dirs = []
        nondirs = []
        for entry in scandir_it:
            if entry.is_dir(follow_symlinks=followlinks):
                dirs.append(entry.name)
            else:
                nondirs.append(entry.name)
    if topdown:
        yield top, dirs, nondirs
    for dirname in dirs:
        new_path = path.join(top, dirname)
        yield from walk(new_path, topdown, onerror, followlinks)
    if not topdown:
        yield top, dirs, nondirs

topdown=True yields a directory before its contents, allowing dirs to be modified in-place to prune subtrees. topdown=False yields leaves first (useful for shutil.rmtree).

os.environ

# CPython: Lib/os.py:690 environ
class _Environ(MutableMapping):
    """Mapping interface to environment variables."""
    def __setitem__(self, key, value):
        putenv(key, value)
        self._data[key] = value

    def __delitem__(self, key):
        unsetenv(key)
        del self._data[key]

os.environ is an _Environ instance initialized at import time from os.environb (bytes-keyed). os.environ['PATH'] = ... calls the C putenv and updates the in-memory dict. Changes are inherited by child processes created with os.fork.

gopy notes

os.scandir is module/os.Scandir in module/os/module.go, wrapping os.ReadDir and returning *DirEntry objects that cache FileInfo. os.walk is a pure-Go recursive generator using Go channels. os.environ is backed by os.Environ() and os.Setenv/os.Unsetenv.