os

os模块提供便捷的与操作系统交互的方法。

1, os.name 

 导入的操作系统相关模块的名称，现在已经注册的有：'posix'，‘nt’,'java'

2, os.uname() 

posix.uname_result(sysname='Linux', nodename='gate02', release='3.10.0-957.5.1.el7.x86_64', version='#1 SMP Fri Feb 1 14:54:57 UTC 2019', machine='x86_64')

用于显示系统相关信息，与sys.platform相似

3, os.ctermid() 

仅unix可用，返回进程控制端对应的文件名

'/dev/tty'

4， os.environ  os.environb 

显示所有环境变量，也可以指定

>>> os.environ['VIVADO_HOME']
'/home/eda/xilinx/Vivado/2017.4'

5, os.chdir(path) 切换路径

6, os.getcwd() 查看当前路径

7, os.fchdir(fd) 通过文件描述符fd切换路径

8, os.getenv(key,defualt=none)  得到环境变量值

>>> os.getenv('VCS_HOME',)
'/home/eda/synopsys/vcs/M-2017.03-SP2-10'

9, os.get_exec_path(env=None)  得到可执行文件的路径

10, os.getegid()  return the effective group id of the current process.--set id--only unix

11, os.geteuid()  return the effective user id of the current process. --only unix

12, os.getgid()  return the real group id of the current process. --only unix

13, os.getgrouplist(user,group)  Return list of group ids that user belongs to. --only unix

>>> os.getgrouplist('yuzhimin',1)
[1, 9002, 9001, 9010, 9003]
>>> os.getgrouplist('yuzhimin',9002)
[9002, 9001, 9010, 9003]

与linux下： id user 功能类似

14, os.getgroups()  Return list of supplemental group ids associated with the current process. --only unix

>>> os.getgroups()
[9001, 9002, 9003, 9010, 9016, 100251]

与linux下groups功能类似

15, os.getlogin()  Return the name of the user logged in on the controlling terminal of the process

16, os.getpgid(pid)  Return the process group id of the process with process id pid. If pid is 0, the process group id of the current process is returned --only unix

17, os.getpgrp()  Return the id of the current process group.--only unix

18, os.getpid()  Return the current process id

19, os.getppid()  Return the parent’s process id

20, os.listdir(path)  Return a list containing the names of the entries in the directory given by path

21, os.mkdir(path,mode=0o777,*,dir_fd=None)  Create a directory named path with numeric mode mode

22, os.remove(path,*,dir_fd=None)  

23, os.removedirs(path)  

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 ('
' or '
' or '
')

  - 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 = '
'

    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 = '
'

    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")



# 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



    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

参考资料：

https://docs.python.org/zh-cn/3.7/library/os.html#process-management

https://github.com/python/cpython/blob/3.7/Lib/os.py