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"]

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.
if 'posix' in _names:
    name = 'posix'
    linesep = '\n'
    from posix import *
    try:
        from posix import _exit
        __all__.append('_exit')
    except ImportError:
        pass
    import posixpath as path

    try:
        from posix import _have_functions
    except ImportError:
        pass

    import posix
    __all__.extend(_get_exports_list(posix))
    del posix

elif 'nt' in _names:
    name = 'nt'
    linesep = '\r\n'
    from nt import *
    try:
        from nt import _exit
        __all__.append('_exit')
    except ImportError:
        pass
    import ntpath as path

    import nt
    __all__.extend(_get_exports_list(nt))
    del nt

    try:
        from nt import _have_functions
    except ImportError:
        pass

else:
    raise ImportError('no os specific module found')

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

del _names


if _exists("_have_functions"):
    _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: