cosmopolitan/third_party/python/Lib/os.py

r"""OS routines for NT or Posix depending on what system we're on.

This exports:
  - all functions from posix or nt, e.g. unlink, stat, etc.
  - os.path is either posixpath or ntpath
  - os.name is either 'posix' or 'nt'
  - os.curdir is a string representing the current directory (always '.')
  - os.pardir is a string representing the parent directory (always '..')
  - os.sep is the (or a most common) pathname separator ('/' or '\\')
  - os.extsep is the extension separator (always '.')
  - os.altsep is the alternate pathname separator (None or '/')
  - os.pathsep is the component separator used in $PATH etc
  - os.linesep is the line separator in text files ('\r' or '\n' or '\r\n')
  - os.defpath is the default search path for executables
  - os.devnull is the file path of the null device ('/dev/null', etc.)

Programs that import and use 'os' stand a better chance of being
portable between different platforms.  Of course, they must then
only use functions that are defined by all platforms (e.g., unlink
and opendir), and leave all pathname manipulation to os.path
(e.g., split and join).
"""

#'
import abc
import sys, errno
import stat as st

_names = sys.builtin_module_names

# Note:  more names are added to __all__ later.
__all__ = ["altsep", "curdir", "pardir", "sep", "pathsep", "linesep",
           "defpath", "name", "path", "devnull", "SEEK_SET", "SEEK_CUR",
           "SEEK_END", "fsencode", "fsdecode", "get_exec_path", "fdopen",
           "popen", "extsep", "_exit"]

def _exists(name):
    return name in globals()

def _get_exports_list(module):
    try:
        return list(module.__all__)
    except AttributeError:
        return [n for n in dir(module) if n[0] != '_']

# Any new dependencies of the os module and/or changes in path separator
# requires updating importlib as well.
name = 'posix'
linesep = '\n'

import posixpath as path
import posix

CLD_CONTINUED = posix.CLD_CONTINUED
CLD_DUMPED = posix.CLD_DUMPED
CLD_EXITED = posix.CLD_EXITED
CLD_TRAPPED = posix.CLD_TRAPPED
DirEntry = posix.DirEntry
EX_CANTCREAT = posix.EX_CANTCREAT
EX_CONFIG = posix.EX_CONFIG
EX_DATAERR = posix.EX_DATAERR
EX_IOERR = posix.EX_IOERR
EX_NOHOST = posix.EX_NOHOST
EX_NOINPUT = posix.EX_NOINPUT
EX_NOPERM = posix.EX_NOPERM
EX_NOUSER = posix.EX_NOUSER
EX_OK = posix.EX_OK
EX_OSERR = posix.EX_OSERR
EX_OSFILE = posix.EX_OSFILE
EX_PROTOCOL = posix.EX_PROTOCOL
EX_SOFTWARE = posix.EX_SOFTWARE
EX_TEMPFAIL = posix.EX_TEMPFAIL
EX_UNAVAILABLE = posix.EX_UNAVAILABLE
EX_USAGE = posix.EX_USAGE
F_LOCK = posix.F_LOCK
F_OK = posix.F_OK
F_TEST = posix.F_TEST
F_TLOCK = posix.F_TLOCK
F_ULOCK = posix.F_ULOCK
GRND_NONBLOCK = posix.GRND_NONBLOCK
GRND_NORDRND = posix.GRND_NORDRND
GRND_NOSYSTEM = posix.GRND_NOSYSTEM
GRND_RANDOM = posix.GRND_RANDOM
O_ACCMODE = posix.O_ACCMODE
O_APPEND = posix.O_APPEND
O_ASYNC = posix.O_ASYNC
O_CLOEXEC = posix.O_CLOEXEC
O_CREAT = posix.O_CREAT
O_DIRECT = posix.O_DIRECT
O_DIRECTORY = posix.O_DIRECTORY
O_DSYNC = posix.O_DSYNC
O_EXCL = posix.O_EXCL
O_LARGEFILE = posix.O_LARGEFILE
O_NDELAY = posix.O_NDELAY
O_NOATIME = posix.O_NOATIME
O_NOCTTY = posix.O_NOCTTY
O_NOFOLLOW = posix.O_NOFOLLOW
O_NONBLOCK = posix.O_NONBLOCK
O_PATH = posix.O_PATH
O_RDONLY = posix.O_RDONLY
O_RDWR = posix.O_RDWR
O_RSYNC = posix.O_RSYNC
O_SYNC = posix.O_SYNC
O_TMPFILE = posix.O_TMPFILE
O_TRUNC = posix.O_TRUNC
O_WRONLY = posix.O_WRONLY
POSIX_FADV_DONTNEED = posix.POSIX_FADV_DONTNEED
POSIX_FADV_NOREUSE = posix.POSIX_FADV_NOREUSE
POSIX_FADV_NORMAL = posix.POSIX_FADV_NORMAL
POSIX_FADV_RANDOM = posix.POSIX_FADV_RANDOM
POSIX_FADV_SEQUENTIAL = posix.POSIX_FADV_SEQUENTIAL
POSIX_FADV_WILLNEED = posix.POSIX_FADV_WILLNEED
PRIO_PGRP = posix.PRIO_PGRP
PRIO_PROCESS = posix.PRIO_PROCESS
PRIO_USER = posix.PRIO_USER
RTLD_GLOBAL = posix.RTLD_GLOBAL
RTLD_LAZY = posix.RTLD_LAZY
RTLD_LOCAL = posix.RTLD_LOCAL
RTLD_NOW = posix.RTLD_NOW
R_OK = posix.R_OK
SCHED_BATCH = posix.SCHED_BATCH
SCHED_FIFO = posix.SCHED_FIFO
SCHED_IDLE = posix.SCHED_IDLE
SCHED_OTHER = posix.SCHED_OTHER
SCHED_RESET_ON_FORK = posix.SCHED_RESET_ON_FORK
SCHED_RR = posix.SCHED_RR
ST_APPEND = posix.ST_APPEND
ST_MANDLOCK = posix.ST_MANDLOCK
ST_NOATIME = posix.ST_NOATIME
ST_NODEV = posix.ST_NODEV
ST_NODIRATIME = posix.ST_NODIRATIME
ST_NOEXEC = posix.ST_NOEXEC
ST_NOSUID = posix.ST_NOSUID
ST_RDONLY = posix.ST_RDONLY
ST_RELATIME = posix.ST_RELATIME
ST_SYNCHRONOUS = posix.ST_SYNCHRONOUS
ST_WRITE = posix.ST_WRITE
WCONTINUED = posix.WCONTINUED
WCOREDUMP = posix.WCOREDUMP
WEXITED = posix.WEXITED
WEXITSTATUS = posix.WEXITSTATUS
WIFCONTINUED = posix.WIFCONTINUED
WIFEXITED = posix.WIFEXITED
WIFSIGNALED = posix.WIFSIGNALED
WIFSTOPPED = posix.WIFSTOPPED
WNOHANG = posix.WNOHANG
WNOWAIT = posix.WNOWAIT
WSTOPPED = posix.WSTOPPED
WSTOPSIG = posix.WSTOPSIG
WTERMSIG = posix.WTERMSIG
WUNTRACED = posix.WUNTRACED
W_OK = posix.W_OK
X_OK = posix.X_OK
_exit = posix._exit
_have_functions = posix._have_functions
abort = posix.abort
access = posix.access
chdir = posix.chdir
chmod = posix.chmod
chown = posix.chown
chroot = posix.chroot
close = posix.close
closerange = posix.closerange
cpu_count = posix.cpu_count
device_encoding = posix.device_encoding
dup = posix.dup
dup2 = posix.dup2
environ = posix.environ
error = posix.error
execv = posix.execv
execve = posix.execve
fchdir = posix.fchdir
fchmod = posix.fchmod
fchown = posix.fchown
fdatasync = posix.fdatasync
fork = posix.fork
fpathconf = posix.fpathconf
fspath = posix.fspath
fstat = posix.fstat
fsync = posix.fsync
ftruncate = posix.ftruncate
get_blocking = posix.get_blocking
get_inheritable = posix.get_inheritable
get_terminal_size = posix.get_terminal_size
getcwd = posix.getcwd
getcwdb = posix.getcwdb
getgrouplist = posix.getgrouplist
getgroups = posix.getgroups
getlogin = posix.getlogin
getpgid = posix.getpgid
getpgrp = posix.getpgrp
getpid = posix.getpid
getpriority = posix.getpriority
getsid = posix.getsid
getuid = posix.getuid
initgroups = posix.initgroups
isatty = posix.isatty
kill = posix.kill
killpg = posix.killpg
lchown = posix.lchown
link = posix.link
listdir = posix.listdir
lseek = posix.lseek
lstat = posix.lstat
major = posix.major
makedev = posix.makedev
minor = posix.minor
mkdir = posix.mkdir
mkfifo = posix.mkfifo
mknod = posix.mknod
nice = posix.nice
open = posix.open
openpty = posix.openpty
pathconf = posix.pathconf
pathconf_names = posix.pathconf_names
pipe = posix.pipe
pipe2 = posix.pipe2
posix_fadvise = posix.posix_fadvise
pread = posix.pread
putenv = posix.putenv
pwrite = posix.pwrite
read = posix.read
readlink = posix.readlink
readv = posix.readv
remove = posix.remove
rename = posix.rename
replace = posix.replace
rmdir = posix.rmdir
scandir = posix.scandir
sched_yield = posix.sched_yield
sendfile = posix.sendfile
set_blocking = posix.set_blocking
set_inheritable = posix.set_inheritable
setegid = posix.setegid
seteuid = posix.seteuid
setgid = posix.setgid
setpgid = posix.setpgid
setpriority = posix.setpriority
setregid = posix.setregid
setresgid = posix.setresgid
setresuid = posix.setresuid
setreuid = posix.setreuid
setsid = posix.setsid
setuid = posix.setuid
stat = posix.stat
stat_float_times = posix.stat_float_times
stat_result = posix.stat_result
statvfs_result = posix.statvfs_result
strerror = posix.strerror
symlink = posix.symlink
sync = posix.sync
sysconf = posix.sysconf
sysconf_names = posix.sysconf_names
system = posix.system
tcgetpgrp = posix.tcgetpgrp
tcsetpgrp = posix.tcsetpgrp
terminal_size = posix.terminal_size
times = posix.times
times_result = posix.times_result
truncate = posix.truncate
umask = posix.umask
uname = posix.uname
uname_result = posix.uname_result
unlink = posix.unlink
unsetenv = posix.unsetenv
urandom = posix.urandom
utime = posix.utime
wait = posix.wait
wait3 = posix.wait3
wait4 = posix.wait4
waitpid = posix.waitpid
write = posix.write
writev = posix.writev

__all__.extend(_get_exports_list(posix))
del posix

sys.modules['os.path'] = path
from os.path import (curdir, pardir, sep, pathsep, defpath, extsep, altsep,
    devnull)

del _names


_globals = globals()
def _add(str, fn):
    if (fn in _globals) and (str in _have_functions):
        _set.add(_globals[fn])

_set = set()
_add("HAVE_FACCESSAT",  "access")
_add("HAVE_FCHMODAT",   "chmod")
_add("HAVE_FCHOWNAT",   "chown")
_add("HAVE_FSTATAT",    "stat")
_add("HAVE_FUTIMESAT",  "utime")
_add("HAVE_LINKAT",     "link")
_add("HAVE_MKDIRAT",    "mkdir")
_add("HAVE_MKFIFOAT",   "mkfifo")
_add("HAVE_MKNODAT",    "mknod")
_add("HAVE_OPENAT",     "open")
_add("HAVE_READLINKAT", "readlink")
_add("HAVE_RENAMEAT",   "rename")
_add("HAVE_SYMLINKAT",  "symlink")
_add("HAVE_UNLINKAT",   "unlink")
_add("HAVE_UNLINKAT",   "rmdir")
_add("HAVE_UTIMENSAT",  "utime")
supports_dir_fd = _set

_set = set()
_add("HAVE_FACCESSAT",  "access")
supports_effective_ids = _set

_set = set()
_add("HAVE_FCHDIR",     "chdir")
_add("HAVE_FCHMOD",     "chmod")
_add("HAVE_FCHOWN",     "chown")
_add("HAVE_FDOPENDIR",  "listdir")
_add("HAVE_FEXECVE",    "execve")
_set.add(stat) # fstat always works
_add("HAVE_FTRUNCATE",  "truncate")
_add("HAVE_FUTIMENS",   "utime")
_add("HAVE_FUTIMES",    "utime")
_add("HAVE_FPATHCONF",  "pathconf")
if _exists("statvfs") and _exists("fstatvfs"): # mac os x10.3
    _add("HAVE_FSTATVFS", "statvfs")
supports_fd = _set

_set = set()
_add("HAVE_FACCESSAT",  "access")
# Some platforms don't support lchmod().  Often the function exists
# anyway, as a stub that always returns ENOSUP or perhaps EOPNOTSUPP.
# (No, I don't know why that's a good design.)  ./configure will detect
# this and reject it--so HAVE_LCHMOD still won't be defined on such
# platforms.  This is Very Helpful.
#
# However, sometimes platforms without a working lchmod() *do* have
# fchmodat().  (Examples: Linux kernel 3.2 with glibc 2.15,
# OpenIndiana 3.x.)  And fchmodat() has a flag that theoretically makes
# it behave like lchmod().  So in theory it would be a suitable
# replacement for lchmod().  But when lchmod() doesn't work, fchmodat()'s
# flag doesn't work *either*.  Sadly ./configure isn't sophisticated
# enough to detect this condition--it only determines whether or not
# fchmodat() minimally works.
#
# Therefore we simply ignore fchmodat() when deciding whether or not
# os.chmod supports follow_symlinks.  Just checking lchmod() is
# sufficient.  After all--if you have a working fchmodat(), your
# lchmod() almost certainly works too.
#
# _add("HAVE_FCHMODAT",   "chmod")
_add("HAVE_FCHOWNAT",   "chown")
_add("HAVE_FSTATAT",    "stat")
_add("HAVE_LCHFLAGS",   "chflags")
_add("HAVE_LCHMOD",     "chmod")
if _exists("lchown"): # mac os x10.3
    _add("HAVE_LCHOWN", "chown")
_add("HAVE_LINKAT",     "link")
_add("HAVE_LUTIMES",    "utime")
_add("HAVE_LSTAT",      "stat")
_add("HAVE_FSTATAT",    "stat")
_add("HAVE_UTIMENSAT",  "utime")
_add("MS_WINDOWS",      "stat")
supports_follow_symlinks = _set

del _set
del _have_functions
del _globals
del _add


# Python uses fixed values for the SEEK_ constants; they are mapped
# to native constants if necessary in posixmodule.c
# Other possible SEEK values are directly imported from posixmodule.c
SEEK_SET = 0
SEEK_CUR = 1
SEEK_END = 2

# Super directory utilities.
# (Inspired by Eric Raymond; the doc strings are mostly his)

def makedirs(name, mode=0o777, exist_ok=False):
    """makedirs(name [, mode=0o777][, exist_ok=False])

    Super-mkdir; create a leaf directory and all intermediate ones.  Works like
    mkdir, except that any intermediate path segment (not just the rightmost)
    will be created if it does not exist. If the target directory already
    exists, raise an OSError if exist_ok is False. Otherwise no exception is
    raised.  This is recursive.

    """
    head, tail = path.split(name)
    if not tail:
        head, tail = path.split(head)
    if head and tail and not path.exists(head):
        try:
            makedirs(head, mode, exist_ok)
        except FileExistsError:
            # Defeats race condition when another thread created the path
            pass
        cdir = curdir
        if isinstance(tail, bytes):
            cdir = bytes(curdir, 'ASCII')
        if tail == cdir:           # xxx/newdir/. exists if xxx/newdir exists
            return
    try:
        mkdir(name, mode)
    except OSError:
        # Cannot rely on checking for EEXIST, since the operating system
        # could give priority to other errors like EACCES or EROFS
        if not exist_ok or not path.isdir(name):
            raise

def removedirs(name):
    """removedirs(name)

    Super-rmdir; remove a leaf directory and all empty intermediate
    ones.  Works like rmdir except that, if the leaf directory is
    successfully removed, directories corresponding to rightmost path
    segments will be pruned away until either the whole path is
    consumed or an error occurs.  Errors during this latter phase are
    ignored -- they generally mean that a directory was not empty.

    """
    rmdir(name)
    head, tail = path.split(name)
    if not tail:
        head, tail = path.split(head)
    while head and tail:
        try:
            rmdir(head)
        except OSError:
            break
        head, tail = path.split(head)

def renames(old, new):
    """renames(old, new)

    Super-rename; create directories as necessary and delete any left
    empty.  Works like rename, except creation of any intermediate
    directories needed to make the new pathname good is attempted
    first.  After the rename, directories corresponding to rightmost
    path segments of the old name will be pruned until either the
    whole path is consumed or a nonempty directory is found.

    Note: this function can fail with the new directory structure made
    if you lack permissions needed to unlink the leaf directory or
    file.

    """
    head, tail = path.split(new)
    if head and tail and not path.exists(head):
        makedirs(head)
    rename(old, new)
    head, tail = path.split(old)
    if head and tail:
        try:
            removedirs(head)
        except OSError:
            pass

__all__.extend(["makedirs", "removedirs", "renames"])

def walk(top, topdown=True, onerror=None, followlinks=False):
    """Directory tree generator.

    For each directory in the directory tree rooted at top (including top
    itself, but excluding '.' and '..'), yields a 3-tuple

        dirpath, dirnames, filenames

    dirpath is a string, the path to the directory.  dirnames is a list of
    the names of the subdirectories in dirpath (excluding '.' and '..').
    filenames is a list of the names of the non-directory files in dirpath.
    Note that the names in the lists are just names, with no path components.
    To get a full path (which begins with top) to a file or directory in
    dirpath, do os.path.join(dirpath, name).

    If optional arg 'topdown' is true or not specified, the triple for a
    directory is generated before the triples for any of its subdirectories
    (directories are generated top down).  If topdown is false, the triple
    for a directory is generated after the triples for all of its
    subdirectories (directories are generated bottom up).

    When topdown is true, the caller can modify the dirnames list in-place
    (e.g., via del or slice assignment), and walk will only recurse into the
    subdirectories whose names remain in dirnames; this can be used to prune the
    search, or to impose a specific order of visiting.  Modifying dirnames when
    topdown is false is ineffective, since the directories in dirnames have
    already been generated by the time dirnames itself is generated. No matter
    the value of topdown, the list of subdirectories is retrieved before the
    tuples for the directory and its subdirectories are generated.

    By default errors from the os.scandir() call are ignored.  If
    optional arg 'onerror' is specified, it should be a function; it
    will be called with one argument, an OSError instance.  It can
    report the error to continue with the walk, or raise the exception
    to abort the walk.  Note that the filename is available as the
    filename attribute of the exception object.

    By default, os.walk does not follow symbolic links to subdirectories on
    systems that support them.  In order to get this functionality, set the
    optional argument 'followlinks' to true.

    Caution:  if you pass a relative pathname for top, don't change the
    current working directory between resumptions of walk.  walk never
    changes the current directory, and assumes that the client doesn't
    either.

    Example:

    import os
    from os.path import join, getsize
    for root, dirs, files in os.walk('python/Lib/email'):
        print(root, "consumes", end="")
        print(sum([getsize(join(root, name)) for name in files]), end="")
        print("bytes in", len(files), "non-directory files")
        if 'CVS' in dirs:
            dirs.remove('CVS')  # don't visit CVS directories

    """
    top = fspath(top)
    dirs = []
    nondirs = []
    walk_dirs = []

    # We may not have read permission for top, in which case we can't
    # get a list of the files the directory contains.  os.walk
    # always suppressed the exception then, rather than blow up for a
    # minor reason when (say) a thousand readable directories are still
    # left to visit.  That logic is copied here.
    try:
        # Note that scandir is global in this module due
        # to earlier import-*.
        scandir_it = scandir(top)
    except OSError as error:
        if onerror is not None:
            onerror(error)
        return

    with scandir_it:
        while True:
            try:
                try:
                    entry = next(scandir_it)
                except StopIteration:
                    break
            except OSError as error:
                if onerror is not None:
                    onerror(error)
                return

            try:
                is_dir = entry.is_dir()
            except OSError:
                # If is_dir() raises an OSError, consider that the entry is not
                # a directory, same behaviour than os.path.isdir().
                is_dir = False

            if is_dir:
                dirs.append(entry.name)
            else:
                nondirs.append(entry.name)

            if not topdown and is_dir:
                # Bottom-up: recurse into sub-directory, but exclude symlinks to
                # directories if followlinks is False
                if followlinks:
                    walk_into = True
                else:
                    try:
                        is_symlink = entry.is_symlink()
                    except OSError:
                        # If is_symlink() raises an OSError, consider that the
                        # entry is not a symbolic link, same behaviour than
                        # os.path.islink().
                        is_symlink = False
                    walk_into = not is_symlink

                if walk_into:
                    walk_dirs.append(entry.path)

    # Yield before recursion if going top down
    if topdown:
        yield top, dirs, nondirs

        # Recurse into sub-directories
        islink, join = path.islink, path.join
        for dirname in dirs:
            new_path = join(top, dirname)
            # Issue #23605: os.path.islink() is used instead of caching
            # entry.is_symlink() result during the loop on os.scandir() because
            # the caller can replace the directory entry during the "yield"
            # above.
            if followlinks or not islink(new_path):
                yield from walk(new_path, topdown, onerror, followlinks)
    else:
        # Recurse into sub-directories
        for new_path in walk_dirs:
            yield from walk(new_path, topdown, onerror, followlinks)
        # Yield after recursion if going bottom up
        yield top, dirs, nondirs

__all__.append("walk")

if {open, stat} <= supports_dir_fd and {listdir, stat} <= supports_fd:

    def fwalk(top=".", topdown=True, onerror=None, *, follow_symlinks=False, dir_fd=None):
        """Directory tree generator.

        This behaves exactly like walk(), except that it yields a 4-tuple

            dirpath, dirnames, filenames, dirfd

        `dirpath`, `dirnames` and `filenames` are identical to walk() output,
        and `dirfd` is a file descriptor referring to the directory `dirpath`.

        The advantage of fwalk() over walk() is that it's safe against symlink
        races (when follow_symlinks is False).

        If dir_fd is not None, it should be a file descriptor open to a directory,
          and top should be relative; top will then be relative to that directory.
          (dir_fd is always supported for fwalk.)

        Caution:
        Since fwalk() yields file descriptors, those are only valid until the
        next iteration step, so you should dup() them if you want to keep them
        for a longer period.

        Example:

        import os
        for root, dirs, files, rootfd in os.fwalk('python/Lib/email'):
            print(root, "consumes", end="")
            print(sum([os.stat(name, dir_fd=rootfd).st_size for name in files]),
                  end="")
            print("bytes in", len(files), "non-directory files")
            if 'CVS' in dirs:
                dirs.remove('CVS')  # don't visit CVS directories
        """
        if not isinstance(top, int) or not hasattr(top, '__index__'):
            top = fspath(top)
        # Note: To guard against symlink races, we use the standard
        # lstat()/open()/fstat() trick.
        orig_st = stat(top, follow_symlinks=False, dir_fd=dir_fd)
        topfd = open(top, O_RDONLY, dir_fd=dir_fd)
        try:
            if (follow_symlinks or (st.S_ISDIR(orig_st.st_mode) and
                                    path.samestat(orig_st, stat(topfd)))):
                yield from _fwalk(topfd, top, topdown, onerror, follow_symlinks)
        finally:
            close(topfd)

    def _fwalk(topfd, toppath, topdown, onerror, follow_symlinks):
        # Note: This uses O(depth of the directory tree) file descriptors: if
        # necessary, it can be adapted to only require O(1) FDs, see issue
        # #13734.

        names = listdir(topfd)
        dirs, nondirs = [], []
        for name in names:
            try:
                # Here, we don't use AT_SYMLINK_NOFOLLOW to be consistent with
                # walk() which reports symlinks to directories as directories.
                # We do however check for symlinks before recursing into
                # a subdirectory.
                if st.S_ISDIR(stat(name, dir_fd=topfd).st_mode):
                    dirs.append(name)
                else:
                    nondirs.append(name)
            except OSError:
                try:
                    # Add dangling symlinks, ignore disappeared files
                    if st.S_ISLNK(stat(name, dir_fd=topfd, follow_symlinks=False)
                                .st_mode):
                        nondirs.append(name)
                except OSError:
                    continue

        if topdown:
            yield toppath, dirs, nondirs, topfd

        for name in dirs:
            try:
                orig_st = stat(name, dir_fd=topfd, follow_symlinks=follow_symlinks)
                dirfd = open(name, O_RDONLY, dir_fd=topfd)
            except OSError as err:
                if onerror is not None:
                    onerror(err)
                continue
            try:
                if follow_symlinks or path.samestat(orig_st, stat(dirfd)):
                    dirpath = path.join(toppath, name)
                    yield from _fwalk(dirfd, dirpath, topdown, onerror, follow_symlinks)
            finally:
                close(dirfd)

        if not topdown:
            yield toppath, dirs, nondirs, topfd

    __all__.append("fwalk")

# Make sure os.environ exists, at least
try:
    environ
except NameError:
    environ = {}

def execl(file, *args):
    """execl(file, *args)

    Execute the executable file with argument list args, replacing the
    current process. """
    execv(file, args)

def execle(file, *args):
    """execle(file, *args, env)

    Execute the executable file with argument list args and
    environment env, replacing the current process. """
    env = args[-1]
    execve(file, args[:-1], env)

def execlp(file, *args):
    """execlp(file, *args)

    Execute the executable file (which is searched for along $PATH)
    with argument list args, replacing the current process. """
    execvp(file, args)

def execlpe(file, *args):
    """execlpe(file, *args, env)

    Execute the executable file (which is searched for along $PATH)
    with argument list args and environment env, replacing the current
    process. """
    env = args[-1]
    execvpe(file, args[:-1], env)

def execvp(file, args):
    """execvp(file, args)

    Execute the executable file (which is searched for along $PATH)
    with argument list args, replacing the current process.
    args may be a list or tuple of strings. """
    _execvpe(file, args)

def execvpe(file, args, env):
    """execvpe(file, args, env)

    Execute the executable file (which is searched for along $PATH)
    with argument list args and environment env , replacing the
    current process.
    args may be a list or tuple of strings. """
    _execvpe(file, args, env)

__all__.extend(["execl","execle","execlp","execlpe","execvp","execvpe"])

def _execvpe(file, args, env=None):
    if env is not None:
        exec_func = execve
        argrest = (args, env)
    else:
        exec_func = execv
        argrest = (args,)
        env = environ

    head, tail = path.split(file)
    if head:
        exec_func(file, *argrest)
        return
    last_exc = saved_exc = None
    saved_tb = None
    path_list = get_exec_path(env)
    if name != 'nt':
        file = fsencode(file)
        path_list = map(fsencode, path_list)
    for dir in path_list:
        fullname = path.join(dir, file)
        try:
            exec_func(fullname, *argrest)
        except OSError as e:
            last_exc = e
            tb = sys.exc_info()[2]
            if (e.errno != errno.ENOENT and e.errno != errno.ENOTDIR
                and saved_exc is None):
                saved_exc = e
                saved_tb = tb
    if saved_exc:
        raise saved_exc.with_traceback(saved_tb)
    raise last_exc.with_traceback(tb)


def get_exec_path(env=None):
    """Returns the sequence of directories that will be searched for the
    named executable (similar to a shell) when launching a process.

    *env* must be an environment variable dict or None.  If *env* is None,
    os.environ will be used.
    """
    # Use a local import instead of a global import to limit the number of
    # modules loaded at startup: the os module is always loaded at startup by
    # Python. It may also avoid a bootstrap issue.
    import warnings

    if env is None:
        env = environ

    # {b'PATH': ...}.get('PATH') and {'PATH': ...}.get(b'PATH') emit a
    # BytesWarning when using python -b or python -bb: ignore the warning
    with warnings.catch_warnings():
        warnings.simplefilter("ignore", BytesWarning)

        try:
            path_list = env.get('PATH')
        except TypeError:
            path_list = None

        if supports_bytes_environ:
            try:
                path_listb = env[b'PATH']
            except (KeyError, TypeError):
                pass
            else:
                if path_list is not None:
                    raise ValueError(
                        "env cannot contain 'PATH' and b'PATH' keys")
                path_list = path_listb

            if path_list is not None and isinstance(path_list, bytes):
                path_list = fsdecode(path_list)

    if path_list is None:
        path_list = defpath
    return path_list.split(pathsep)


# Change environ to automatically call putenv(), unsetenv if they exist.
from _collections_abc import MutableMapping

class _Environ(MutableMapping):
    def __init__(self, data, encodekey, decodekey, encodevalue, decodevalue, putenv, unsetenv):
        self.encodekey = encodekey
        self.decodekey = decodekey
        self.encodevalue = encodevalue
        self.decodevalue = decodevalue
        self.putenv = putenv
        self.unsetenv = unsetenv
        self._data = data

    def __getitem__(self, key):
        try:
            value = self._data[self.encodekey(key)]
        except KeyError:
            # raise KeyError with the original key value
            raise KeyError(key) from None
        return self.decodevalue(value)

    def __setitem__(self, key, value):
        key = self.encodekey(key)
        value = self.encodevalue(value)
        self.putenv(key, value)
        self._data[key] = value

    def __delitem__(self, key):
        encodedkey = self.encodekey(key)
        self.unsetenv(encodedkey)
        try:
            del self._data[encodedkey]
        except KeyError:
            # raise KeyError with the original key value
            raise KeyError(key) from None

    def __iter__(self):
        # list() from dict object is an atomic operation
        keys = list(self._data)
        for key in keys:
            yield self.decodekey(key)

    def __len__(self):
        return len(self._data)

    def __repr__(self):
        return 'environ({{{}}})'.format(', '.join(
            ('{!r}: {!r}'.format(self.decodekey(key), self.decodevalue(value))
            for key, value in self._data.items())))

    def copy(self):
        return dict(self)

    def setdefault(self, key, value):
        if key not in self:
            self[key] = value
        return self[key]

try:
    _putenv = putenv
except NameError:
    _putenv = lambda key, value: None
else:
    if "putenv" not in __all__:
        __all__.append("putenv")

try:
    _unsetenv = unsetenv
except NameError:
    _unsetenv = lambda key: _putenv(key, "")
else:
    if "unsetenv" not in __all__:
        __all__.append("unsetenv")

def _createenviron():
    if name == 'nt':
        # Where Env Var Names Must Be UPPERCASE
        def check_str(value):
            if not isinstance(value, str):
                raise TypeError("str expected, not %s" % type(value).__name__)
            return value
        encode = check_str
        decode = str
        def encodekey(key):
            return encode(key).upper()
        data = {}
        for key, value in environ.items():
            data[encodekey(key)] = value
    else:
        # Where Env Var Names Can Be Mixed Case
        encoding = sys.getfilesystemencoding()
        def encode(value):
            if not isinstance(value, str):
                raise TypeError("str expected, not %s" % type(value).__name__)
            return value.encode(encoding, 'surrogateescape')
        def decode(value):
            return value.decode(encoding, 'surrogateescape')
        encodekey = encode
        data = environ
    return _Environ(data,
        encodekey, decode,
        encode, decode,
        _putenv, _unsetenv)

# unicode environ
environ = _createenviron()
del _createenviron


def getenv(key, default=None):
    """Get an environment variable, return None if it doesn't exist.
    The optional second argument can specify an alternate default.
    key, default and the result are str."""
    return environ.get(key, default)

supports_bytes_environ = (name != 'nt')
__all__.extend(("getenv", "supports_bytes_environ"))

if supports_bytes_environ:
    def _check_bytes(value):
        if not isinstance(value, bytes):
            raise TypeError("bytes expected, not %s" % type(value).__name__)
        return value

    # bytes environ
    environb = _Environ(environ._data,
        _check_bytes, bytes,
        _check_bytes, bytes,
        _putenv, _unsetenv)
    del _check_bytes

    def getenvb(key, default=None):
        """Get an environment variable, return None if it doesn't exist.
        The optional second argument can specify an alternate default.
        key, default and the result are bytes."""
        return environb.get(key, default)

    __all__.extend(("environb", "getenvb"))

def _fscodec():
    encoding = sys.getfilesystemencoding()
    errors = sys.getfilesystemencodeerrors()

    def fsencode(filename):
        """Encode filename (an os.PathLike, bytes, or str) to the filesystem
        encoding with 'surrogateescape' error handler, return bytes unchanged.
        On Windows, use 'strict' error handler if the file system encoding is
        'mbcs' (which is the default encoding).
        """
        filename = fspath(filename)  # Does type-checking of `filename`.
        if isinstance(filename, str):
            return filename.encode(encoding, errors)
        else:
            return filename

    def fsdecode(filename):
        """Decode filename (an os.PathLike, bytes, or str) from the filesystem
        encoding with 'surrogateescape' error handler, return str unchanged. On
        Windows, use 'strict' error handler if the file system encoding is
        'mbcs' (which is the default encoding).
        """
        filename = fspath(filename)  # Does type-checking of `filename`.
        if isinstance(filename, bytes):
            return filename.decode(encoding, errors)
        else:
            return filename

    return fsencode, fsdecode

fsencode, fsdecode = _fscodec()
del _fscodec

# Supply spawn*() (probably only for Unix)
if _exists("fork") and not _exists("spawnv") and _exists("execv"):

    P_WAIT = 0
    P_NOWAIT = P_NOWAITO = 1

    __all__.extend(["P_WAIT", "P_NOWAIT", "P_NOWAITO"])

    # XXX Should we support P_DETACH?  I suppose it could fork()**2
    # and close the std I/O streams.  Also, P_OVERLAY is the same
    # as execv*()?

    def _spawnvef(mode, file, args, env, func):
        # Internal helper; func is the exec*() function to use
        if not isinstance(args, (tuple, list)):
            raise TypeError('argv must be a tuple or a list')
        if not args or not args[0]:
            raise ValueError('argv first element cannot be empty')
        pid = fork()
        if not pid:
            # Child
            try:
                if env is None:
                    func(file, args)
                else:
                    func(file, args, env)
            except:
                _exit(127)
        else:
            # Parent
            if mode == P_NOWAIT:
                return pid # Caller is responsible for waiting!
            while 1:
                wpid, sts = waitpid(pid, 0)
                if WIFSTOPPED(sts):
                    continue
                elif WIFSIGNALED(sts):
                    return -WTERMSIG(sts)
                elif WIFEXITED(sts):
                    return WEXITSTATUS(sts)
                else:
                    raise OSError("Not stopped, signaled or exited???")

    def spawnv(mode, file, args):
        """spawnv(mode, file, args) -> integer

Execute file with arguments from args in a subprocess.
If mode == P_NOWAIT return the pid of the process.
If mode == P_WAIT return the process's exit code if it exits normally;
otherwise return -SIG, where SIG is the signal that killed it. """
        return _spawnvef(mode, file, args, None, execv)

    def spawnve(mode, file, args, env):
        """spawnve(mode, file, args, env) -> integer

Execute file with arguments from args in a subprocess with the
specified environment.
If mode == P_NOWAIT return the pid of the process.
If mode == P_WAIT return the process's exit code if it exits normally;
otherwise return -SIG, where SIG is the signal that killed it. """
        return _spawnvef(mode, file, args, env, execve)

    # Note: spawnvp[e] isn't currently supported on Windows

    def spawnvp(mode, file, args):
        """spawnvp(mode, file, args) -> integer

Execute file (which is looked for along $PATH) with arguments from
args in a subprocess.
If mode == P_NOWAIT return the pid of the process.
If mode == P_WAIT return the process's exit code if it exits normally;
otherwise return -SIG, where SIG is the signal that killed it. """
        return _spawnvef(mode, file, args, None, execvp)

    def spawnvpe(mode, file, args, env):
        """spawnvpe(mode, file, args, env) -> integer

Execute file (which is looked for along $PATH) with arguments from
args in a subprocess with the supplied environment.
If mode == P_NOWAIT return the pid of the process.
If mode == P_WAIT return the process's exit code if it exits normally;
otherwise return -SIG, where SIG is the signal that killed it. """
        return _spawnvef(mode, file, args, env, execvpe)


    __all__.extend(["spawnv", "spawnve", "spawnvp", "spawnvpe"])


if _exists("spawnv"):
    # These aren't supplied by the basic Windows code
    # but can be easily implemented in Python

    def spawnl(mode, file, *args):
        """spawnl(mode, file, *args) -> integer

Execute file with arguments from args in a subprocess.
If mode == P_NOWAIT return the pid of the process.
If mode == P_WAIT return the process's exit code if it exits normally;
otherwise return -SIG, where SIG is the signal that killed it. """
        return spawnv(mode, file, args)

    def spawnle(mode, file, *args):
        """spawnle(mode, file, *args, env) -> integer

Execute file with arguments from args in a subprocess with the
supplied environment.
If mode == P_NOWAIT return the pid of the process.
If mode == P_WAIT return the process's exit code if it exits normally;
otherwise return -SIG, where SIG is the signal that killed it. """
        env = args[-1]
        return spawnve(mode, file, args[:-1], env)


    __all__.extend(["spawnl", "spawnle"])


if _exists("spawnvp"):
    # At the moment, Windows doesn't implement spawnvp[e],
    # so it won't have spawnlp[e] either.
    def spawnlp(mode, file, *args):
        """spawnlp(mode, file, *args) -> integer

Execute file (which is looked for along $PATH) with arguments from
args in a subprocess with the supplied environment.
If mode == P_NOWAIT return the pid of the process.
If mode == P_WAIT return the process's exit code if it exits normally;
otherwise return -SIG, where SIG is the signal that killed it. """
        return spawnvp(mode, file, args)

    def spawnlpe(mode, file, *args):
        """spawnlpe(mode, file, *args, env) -> integer

Execute file (which is looked for along $PATH) with arguments from
args in a subprocess with the supplied environment.
If mode == P_NOWAIT return the pid of the process.
If mode == P_WAIT return the process's exit code if it exits normally;
otherwise return -SIG, where SIG is the signal that killed it. """
        env = args[-1]
        return spawnvpe(mode, file, args[:-1], env)


    __all__.extend(["spawnlp", "spawnlpe"])


# Supply os.popen()
def popen(cmd, mode="r", buffering=-1):
    if not isinstance(cmd, str):
        raise TypeError("invalid cmd type (%s, expected string)" % type(cmd))
    if mode not in ("r", "w"):
        raise ValueError("invalid mode %r" % mode)
    if buffering == 0 or buffering is None:
        raise ValueError("popen() does not support unbuffered streams")
    try:
        import subprocess, io
    except ImportError:
        raise ImportError('please use subprocess module')
    if mode == "r":
        proc = subprocess.Popen(cmd,
                                shell=True,
                                stdout=subprocess.PIPE,
                                bufsize=buffering)
        return _wrap_close(io.TextIOWrapper(proc.stdout), proc)
    else:
        proc = subprocess.Popen(cmd,
                                shell=True,
                                stdin=subprocess.PIPE,
                                bufsize=buffering)
        return _wrap_close(io.TextIOWrapper(proc.stdin), proc)

# Helper for popen() -- a proxy for a file whose close waits for the process
class _wrap_close:
    def __init__(self, stream, proc):
        self._stream = stream
        self._proc = proc
    def close(self):
        self._stream.close()
        returncode = self._proc.wait()
        if returncode == 0:
            return None
        if name == 'nt':
            return returncode
        else:
            return returncode << 8  # Shift left to match old behavior
    def __enter__(self):
        return self
    def __exit__(self, *args):
        self.close()
    def __getattr__(self, name):
        return getattr(self._stream, name)
    def __iter__(self):
        return iter(self._stream)

# Supply os.fdopen()
def fdopen(fd, *args, **kwargs):
    if not isinstance(fd, int):
        raise TypeError("invalid fd type (%s, expected integer)" % type(fd))
    import io
    return io.open(fd, *args, **kwargs)


# For testing purposes, make sure the function is available when the C
# implementation exists.
def _fspath(path):
    """Return the path representation of a path-like object.

    If str or bytes is passed in, it is returned unchanged. Otherwise the
    os.PathLike interface is used to get the path representation. If the
    path representation is not str or bytes, TypeError is raised. If the
    provided path is not str, bytes, or os.PathLike, TypeError is raised.
    """
    if isinstance(path, (str, bytes)):
        return path

    # Work from the object's type to match method resolution of other magic
    # methods.
    path_type = type(path)
    try:
        path_repr = path_type.__fspath__(path)
    except AttributeError:
        if hasattr(path_type, '__fspath__'):
            raise
        else:
            raise TypeError("expected str, bytes or os.PathLike object, "
                            "not " + path_type.__name__)
    if isinstance(path_repr, (str, bytes)):
        return path_repr
    else:
        raise TypeError("expected {}.__fspath__() to return str or bytes, "
                        "not {}".format(path_type.__name__,
                                        type(path_repr).__name__))

# If there is no C implementation, make the pure Python version the
# implementation as transparently as possible.
if not _exists('fspath'):
    fspath = _fspath
    fspath.__name__ = "fspath"


class PathLike(abc.ABC):

    """Abstract base class for implementing the file system path protocol."""

    @abc.abstractmethod
    def __fspath__(self):
        """Return the file system path representation of the object."""
        raise NotImplementedError

    @classmethod
    def __subclasshook__(cls, subclass):
        return hasattr(subclass, '__fspath__')