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
import stat as st

from _collections_abc import _check_methods

_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_FDOPENDIR", "scandir")
 _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, exist_ok=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 has no effect on the behavior of os.walk(), 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 {scandir, 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.
 if not follow_symlinks:
 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, isinstance(top, bytes),
 topdown, onerror, follow_symlinks)
 finally:
 close(topfd)

 def _fwalk(topfd, toppath, isbytes, 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.

 scandir_it = scandir(topfd)
 dirs = []
 nondirs = []
 entries = None if topdown or follow_symlinks else []
 for entry in scandir_it:
 name = entry.name
 if isbytes:
 name = fsencode(name)
 try:
 if entry.is_dir():
 dirs.append(name)
 if entries is not None:
 entries.append(entry)
 else:
 nondirs.append(name)
 except OSError:
 try:
 # Add dangling symlinks, ignore disappeared files
 if entry.is_symlink():
 nondirs.append(name)
 except OSError:
 pass

 if topdown:
 yield toppath, dirs, nondirs, topfd

 for name in dirs if entries is None else zip(dirs, entries):
 try:
 if not follow_symlinks:
 if topdown:
 orig_st = stat(name, dir_fd=topfd, follow_symlinks=False)
 else:
 assert entries is not None
 name, entry = name
 orig_st = entry.stat(follow_symlinks=False)
 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, isbytes,
 topdown, onerror, follow_symlinks)
 finally:
 close(dirfd)

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

 __all__.append("fwalk")

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

 if path.dirname(file):
 exec_func(file, *argrest)
 return
 saved_exc = 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 (FileNotFoundError, NotADirectoryError) as e:
 last_exc = e
 except OSError as e:
 last_exc = e
 if saved_exc is None:
 saved_exc = e
 if saved_exc is not None:
 raise saved_exc
 raise last_exc


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")
 import subprocess, io
 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):
 if cls is PathLike:
 return _check_methods(subclass, '__fspath__')
 return NotImplemented


if name == 'nt':
 class _AddedDllDirectory:
 def __init__(self, path, cookie, remove_dll_directory):
 self.path = path
 self._cookie = cookie
 self._remove_dll_directory = remove_dll_directory
 def close(self):
 self._remove_dll_directory(self._cookie)
 self.path = None
 def __enter__(self):
 return self
 def __exit__(self, *args):
 self.close()
 def __repr__(self):
 if self.path:
 return "<AddedDllDirectory({!r})>".format(self.path)
 return "<AddedDllDirectory()>"

 def add_dll_directory(path):
 """Add a path to the DLL search path.

 This search path is used when resolving dependencies for imported
 extension modules (the module itself is resolved through sys.path),
 and also by ctypes.

 Remove the directory by calling close() on the returned object or
 using it in a with statement.
 """
 import nt
 cookie = nt._add_dll_directory(path)
 return _AddedDllDirectory(
 path,
 cookie,
 nt._remove_dll_directory
 )