# `os` --- 各种各样的操作系统接口

源代码： Lib/os.py

本模块提供了一种使用与操作系统相关的功能的便捷式途径。 如果你只是想读写一个文件，请参阅 `open()`，如果你想操作文件路径，请参阅 `os.path` 模块，如果你想读取通过命令行给出的所有文件中的所有行，请参阅 `fileinput` 模块。 为了创建临时文件和目录，请参阅 `tempfile` 模块，对于高级文件和目录处理，请参阅 `shutil` 模块。

关于这些函数的可用性的说明：

- Python中所有依赖于操作系统的内置模块的设计都是这样，只要不同的操作系统某一相同的功能可用，它就使用相同的接口。例如，函数 `os.stat(path)` 以相同的格式返回关于 path 的状态信息（该格式源于 POSIX 接口）。

- 特定于某一操作系统的扩展通过操作 `os` 模块也是可用的，但是使用它们当然是对可移植性的一种威胁。

- 所有接受路径或文件名的函数都同时支持字节串和字符串对象，并在返回路径或文件名时使用相应类型的对象作为结果。

- 在 VxWorks 系统上，os.fork, os.execv 和 os.spawn*p* 不被支持。

備註

如果使用无效或无法访问的文件名与路径，或者其他类型正确但操作系统不接受的参数，此模块的所有函数都抛出 `OSError` （或者它的子类）。

exception `os.``error`

  内建的 `OSError` 异常的一个别名。

`os.``name`

  导入的依赖特定操作系统的模块的名称。以下名称目前已注册: `'posix'`, `'nt'`, `'java'`.

  也參考

  `sys.platform` 有更详细的描述. `os.uname()` 只给出系统提供的版本信息。

  `platform` 模块对系统的标识有更详细的检查。

## 文件名，命令行参数，以及环境变量。

在 Python 中，使用字符串类型表示文件名、命令行参数和环境变量。 在某些系统上，在将这些字符串传递给操作系统之前，必须将这些字符串解码为字节。 Python 使用文件系统编码来执行此转换（请参阅 `sys.getfilesystemencoding()` ）。

3.1 版更變: 在某些系统上，使用文件系统编码进行转换可能会失败。 在这种情况下，Python 会使用 代理转义编码错误处理器，这意味着在解码时，不可解码的字节被 Unicode 字符 U+DCxx 替换，并且这些字节在编码时再次转换为原始字节。

文件系统编码必须保证成功解码小于 128 的所有字节。如果文件系统编码无法提供此保证， API 函数可能会引发 UnicodeErrors 。

## 进程参数

这些函数和数据项提供了操作当前进程和用户的信息。

`os.``ctermid`()

  返回与进程控制终端对应的文件名。

  可用性: Unix。

`os.``environ`

  一个表示字符串环境的 mapping 对象。 例如，`environ['HOME']` 是你的主目录（在某些平台上）的路径名，相当于 C 中的 `getenv("HOME")`。

  这个映射是在第一次导入 `os` 模块时捕获的，通常作为 Python 启动时处理 `site.py` 的一部分。除了通过直接修改 `os.environ` 之外，在此之后对环境所做的更改不会反映在 `os.environ` 中。

  如果平台支持 `putenv()` 函数，这个映射除了可以用于查询环境外还能用于修改环境。 当这个映射被修改时，`putenv()` 将被自动调用。

  在Unix系统上，键和值会使用 `sys.getfilesystemencoding()` 和 `'surrogateescape'` 的错误处理。如果你想使用其他的编码，使用 `environb`。

  備註

  直接调用 `putenv()` 并不会影响 `os.environ`，所以推荐直接修改``os.environ``。

  備註

  在某些平台上，包括 FreeBSD 和 Mac OS X，设置 `environ` 可能导致内存泄露。参阅 `putenv()` 的系统文档。

  如果平台没有提供 `putenv()`, 为了使启动的子进程使用修改后的环境，一份修改后的映射会被传给合适的进程创建函数。

  如果平台支持 `unsetenv()` 函数，你可以通过删除映射中元素的方式来删除对应的环境变量。当一个元素被从 `os.environ` 删除时，以及 `pop()` 或 `clear()` 被调用时， `unsetenv()` 会被自动调用。

`os.``environb`

  字节版本的 `environ`: 一个以字节串表示环境的 mapping 对象。 `environ` 和 `environb` 是同步的（修改 `environb` 会更新 `environ`，反之亦然）。

  只有在 `supports_bytes_environ` 为 `True` 的时候 `environb` 才是可用的。

  3.2 版新加入.

`os.``chdir`(path)
`os.``fchdir`(fd)
`os.``getcwd`()

  以上函数请参阅 文件和目录 。

`os.``fsencode`(filename)

  编码 路径类 文件名 为文件系统接受的形式，使用 `'surrogateescape'` 代理转义编码错误处理器，在Windows系统上会使用 `'strict'` ；返回 `bytes` 字节类型不变。

  `fsdecode()` 是此函数的逆向函数。

  3.2 版新加入.

  3.6 版更變: 增加对实现了 `os.PathLike` 接口的对象的支持。

`os.``fsdecode`(filename)

  从文件系统编码方式解码为 路径类 文件名，使用 `'surrogateescape'` 代理转义编码错误处理器，在Windows系统上会使用 `'strict'` ；返回 `str` 字符串不变。

  `fsencode()` 是此函数的逆向函数。

  3.2 版新加入.

  3.6 版更變: 增加对实现了 `os.PathLike` 接口的对象的支持。

`os.``fspath`(path)

  返回路径的文件系统表示。

  如果传入的是 `str` 或 `bytes` 类型的字符串，将原样返回。否则 `__fspath__()` 将被调用，如果得到的是一个 `str` 或 `bytes` 类型的对象，那就返回这个值。其他所有情况则会抛出 `TypeError` 异常。

  3.6 版新加入.

class `os.``PathLike`

  描述表示一个文件系统路径的 abstract base class ，如 `pathlib.PurePath` 。

  3.6 版新加入.

  abstractmethod `__fspath__`()

    返回当前对象的文件系统表示。

    这个方法只应该返回一个 `str` 字符串或 `bytes` 字节串，请优先选择 `str` 字符串。

`os.``getenv`(key, default=None)

  如果存在，返回环境变量 key 的值，否则返回 default。 key ， default 和返回值均为 str 字符串类型。

  在Unix系统上，键和值会使用 `sys.getfilesystemencoding()` 和``'surrogateescape'`` 错误处理进行解码。如果你想使用其他的编码，使用 `os.getenvb()`。

  可用性: 大部分的Unix系统，Windows。

`os.``getenvb`(key, default=None)

  如果存在环境变量 key 那么返回其值，否则返回 default。 key ， default 和返回值均为bytes字节串类型。

  `getenvb()` 仅在 `supports_bytes_environ` 为 `True` 时可用。

  可用性: 大部分的Unix系统。

  3.2 版新加入.

`os.``get_exec_path`(env=None)

  返回将用于搜索可执行文件的目录列表，与在外壳程序中启动一个进程时相似。指定的 env 应为用于搜索 PATH 的环境变量字典。默认情况下，当 env 为 `None` 时，将会使用 `environ` 。

  3.2 版新加入.

`os.``getegid`()

  返回当前进程的有效组ID。对应当前进程执行文件的 "set id" 位。

  可用性: Unix。

`os.``geteuid`()

  返回当前进程的有效用户ID。

  可用性: Unix。

`os.``getgid`()

  返回当前进程的实际组ID。

  可用性: Unix。

`os.``getgrouplist`(user, group)

  返回该用户所在的组 ID 列表。可能 group 参数没有在返回的列表中，实际上用户应该也是属于该 group。group 参数一般可以从储存账户信息的密码记录文件中找到。

  可用性: Unix。

  3.3 版新加入.

`os.``getgroups`()

  返回当前进程对应的组ID列表

  可用性: Unix。

  備註

  在Mac OS X系统中，`getgroups()` 会和其他 Unix 平台有些不同。如果 Python 解释器是在 `10.5` 或更早版本中部署，`getgroups()` 返回当前用户进程相关的有效组ID列表。 该列表长度由于系统预设的接口限制，最长为 16。 而且在适当的权限下，返回结果还会因 `getgroups()` 而发生变化；如果 Python 解释器是在 `10.5` 以上版本中部署，`getgroups()` 返回进程所属有效用户 ID 所对应的用户的组 ID 列表，组用户列表可能因为进程的生存周期而发生变动，而且也不会因为 `setgroups()` 的调用而发生，返回的组用户列表长度也没有长度 16 的限制。在部署中，Python 解释器用到的变量 `MACOSX_DEPLOYMENT_TARGET` 可以用 `sysconfig.get_config_var()`。

`os.``getlogin`()

  返回通过控制终端进程进行登录的用户名。在多数情况下，使用 `getpass.getuser()` 会更有效，因为后者会通过检查环境变量 `LOGNAME` 或 `USERNAME` 来查找用户，再由 `pwd.getpwuid(os.getuid())[0]` 来获取当前用户 ID 的登录名。

  可用性: Unix, Windows。

`os.``getpgid`(pid)

  根据进程id pid 返回进程的组 ID 列表。如果 pid 为 0，则返回当前进程的进程组 ID 列表

  可用性: Unix。

`os.``getpgrp`()

  返回当时进程组的ID

  可用性: Unix。

`os.``getpid`()

  返回当前进程ID

`os.``getppid`()

  返回父进程ID。当父进程已经结束，在Unix中返回的ID是初始进程(1)中的一个，在Windows中仍然是同一个进程ID，该进程ID有可能已经被进行进程所占用。

  可用性: Unix, Windows。

  3.2 版更變: 添加WIndows的支持。

`os.``getpriority`(which, who)

  获取程序调度优先级。which 参数值可以是 `PRIO_PROCESS`，`PRIO_PGRP`，或 `PRIO_USER` 中的一个，who 是相对于 which (`PRIO_PROCESS` 的进程标识符，`PRIO_PGRP` 的进程组标识符和 `PRIO_USER` 的用户ID)。当 who 为 0 时（分别）表示调用的进程，调用进程的进程组或调用进程所属的真实用户 ID。

  可用性: Unix。

  3.3 版新加入.

`os.``PRIO_PROCESS`
`os.``PRIO_PGRP`
`os.``PRIO_USER`

  函数 `getpriority()` 和 `setpriority()` 的参数。

  可用性: Unix。

  3.3 版新加入.

`os.``getresuid`()

  返回一个由 (ruid, euid, suid) 所组成的元组，分别表示当前进程的真实用户ID，有效用户ID和甲暂存用户ID。

  可用性: Unix。

  3.2 版新加入.

`os.``getresgid`()

  返回一个由 (rgid, egid, sgid) 所组成的元组，分别表示当前进程的真实组ID，有效组ID和暂存组ID。

  可用性: Unix。

  3.2 版新加入.

`os.``getuid`()

  返回当前进程的真实用户ID。

  可用性: Unix。

`os.``initgroups`(username, gid)

  调用系统 initgroups()，使用指定用户所在的所有值来初始化组访问列表，包括指定的组ID。

  可用性: Unix。

  3.2 版新加入.

`os.``putenv`(key, value)

  将名为 key 的环境变量值设置为 value。该变量名修改会影响由 `os.system()`， `popen()` ，`fork()` 和 `execv()` 发起的子进程。

  可用性: 大部分的Unix系统，Windows。

  備註

  在一些平台，包括 FreeBSD 和 Mac OS X，设置 `environ` 可能导致内存泄露。详情参考 putenv 相关系统文档。

  当系统支持 `putenv()` 时，`os.environ` 中的参数赋值会自动转换为对 `putenv()` 的调用。不过 `putenv()` 的调用不会更新 `os.environ`，因此最好使用 `os.environ` 对变量赋值。

`os.``setegid`(egid)

  设置当前进程的有效组ID。

  可用性: Unix。

`os.``seteuid`(euid)

  设置当前进程的有效用户ID。

  可用性: Unix。

`os.``setgid`(gid)

  设置当前进程的组ID。

  可用性: Unix。

`os.``setgroups`(groups)

  将 group 参数值设置为与当进程相关联的附加组ID列表。group 参数必须为一个序列，每个元素应为每个组的数字ID。该操作通常只适用于超级用户。

  可用性: Unix。

  備註

  在 Mac OS X 中，groups 的长度不能超过系统定义的最大有效组 ID 个数，一般为 16。 如果它没有返回与调用 setgroups() 所设置的相同的组列表，请参阅 `getgroups()` 的文档。

`os.``setpgrp`()

  根据已实现的版本（如果有）来调用系统 `setpgrp()` 或 `setpgrp(0, 0)` 。相关说明，请参考 Unix 手册。

  可用性: Unix。

`os.``setpgid`(pid, pgrp)

  使用系统调用 `setpgid()`，将 pid 对应进程的组ID设置为 pgrp。相关说明，请参考 Unix 手册。

  可用性: Unix。

`os.``setpriority`(which, who, priority)

  设置程序调度优先级。 which 的值为 `PRIO_PROCESS`, `PRIO_PGRP` 或 `PRIO_USER` 之一，而 who 会相对于 which (`PRIO_PROCESS` 的进程标识符, `PRIO_PGRP` 的进程组标识符和 `PRIO_USER` 的用户 ID) 被解析。 who 值为零 (分别) 表示调用进程，调用进程的进程组或调用进程的真实用户 ID。 priority 是范围在 -20 至 19 的值。 默认优先级为 0；较小的优先级数值会更优先被调度。

  可用性: Unix。

  3.3 版新加入.

`os.``setregid`(rgid, egid)

  设置当前进程的真实和有效组ID。

  可用性: Unix。

`os.``setresgid`(rgid, egid, sgid)

  设置当前进程的真实，有效和暂存组ID。

  可用性: Unix。

  3.2 版新加入.

`os.``setresuid`(ruid, euid, suid)

  设置当前进程的真实，有效和暂存用户ID。

  可用性: Unix。

  3.2 版新加入.

`os.``setreuid`(ruid, euid)

  设置当前进程的真实和有效用户ID。

  可用性: Unix。

`os.``getsid`(pid)

  调用系统调用 `getsid()`。相关说明，请参考 Unix 手册。

  可用性: Unix。

`os.``setsid`()

  使用系统调用 `getsid()`。相关说明，请参考 Unix 手册。

  可用性: Unix。

`os.``setuid`(uid)

  设置当前进程的用户ID。

  可用性: Unix。

`os.``strerror`(code)

  根据 code 中的错误码返回错误消息。 在某些平台上当给出未知错误码时 `strerror()` 将返回 `NULL` 并会引发 `ValueError`。

`os.``supports_bytes_environ`

  如果操作系统上原生环境类型是字节型则为 `True` (例如在 Windows 上为 `False`)。

  3.2 版新加入.

`os.``umask`(mask)

  设定当前数值掩码并返回之前的掩码。

`os.``uname`()

  返回当前操作系统的识别信息。返回值是一个有5个属性的对象：

  - `sysname` - 操作系统名

  - `nodename` - 机器在网络上的名称（需要先设定）

  - `release` - 操作系统发行信息

  - `version` - 操作系统版本信息

  - `machine` - 硬件标识符

  为了向后兼容，该对象也是可迭代的，像是一个按照 `sysname`，`nodename`，`release`，`version`，和 `machine` 顺序组成的元组。

  有些系统会将 `nodename` 截短为 8 个字符或截短至前缀部分；获取主机名的一个更好方式是 `socket.gethostname()` 或甚至可以用 `socket.gethostbyaddr(socket.gethostname())`。

  可用性: 较新的 Unix 版本。

  3.3 版更變: 返回结果的类型由元组变成一个类似元组的对象，同时具有命名的属性。

`os.``unsetenv`(key)

  取消设置（删除）名为 key 的环境变量。变量名的改变会影响由 `os.system()`，`popen()`，`fork()` 和 `execv()` 触发的子进程。

  当系统支持 `unsetenv()` ，删除在 `os.environ` 中的变量会自动转换为对 `unsetenv()` 的调用。但是 `unsetenv()` 不能更新 `os.environ`，因此最好直接删除 `os.environ` 中的变量。

  可用性: 大部分的Unix系统，Windows。

## 创建文件对象

这些函数创建新的 file objects 。（参见 `open()` 以获取打开文件描述符的相关信息。）

`os.``fdopen`(fd, *args, **kwargs)

  返回打开文件描述符 fd 对应文件的对象。类似内建 `open()` 函数，二者接受同样的参数。不同之处在于 `fdopen()` 第一个参数应该为整数。

## 文件描述符操作

这些函数对文件描述符所引用的 I/O 流进行操作。

文件描述符是一些小的整数，对应于当前进程所打开的文件。例如，标准输入的文件描述符通常是0，标准输出是1，标准错误是2。之后被进程打开的文件的文件描述符会被依次指定为3，4，5等。“文件描述符”这个词有点误导性，在 Unix 平台中套接字和管道也被文件描述符所引用。

当需要时，可以用 `fileno()` 可以获得 file object 所对应的文件描述符。需要注意的是，直接使用文件描述符会绕过文件对象的方法，会忽略如数据内部缓冲等情况。

`os.``close`(fd)

  关闭文件描述符 fd。

  備註

  该功能适用于低级 I/O 操作，必须用于 `os.open()` 或 `pipe()` 返回的文件描述符。若要关闭由内建函数 `open()`、`popen()` 或 `fdopen()` 返回的 "文件对象"，则应使用其相应的 `close()` 方法。

`os.``closerange`(fd_low, fd_high)

  关闭从 fd_low （包括）到 fd_high （排除）间的文件描述符，并忽略错误。类似（但快于）:

      for fd in range(fd_low, fd_high):
          try:
              os.close(fd)
          except OSError:
              pass

`os.``copy_file_range`(src, dst, count, offset_src=None, offset_dst=None)

  从文件描述符 src 复制 count 字节，从偏移量 offset_src 开始读取，到文件描述符 dst，从偏移量 offset_dst 开始写入。如果 offset_src 为 None，则 src 将从当前位置开始读取；offset_dst 同理。src 和 dst 指向的文件必须处于相同的文件系统，否则将会抛出一个 `errno` 被设为 `errno.EXDEV` 的 `OSError` 。

  此复制的完成没有额外的从内核到用户空间再回到内核的数据转移花费。另外，一些文件系统可能实现额外的优化。完成复制就如同打开两个二进制文件一样。

  返回值是复制的字节的数目。这可能低于需求的数目。

  Availability: Linux kernel >= 4.5 或 glibc >= 2.27。

  3.8 版新加入.

`os.``device_encoding`(fd)

  如果连接到终端，则返回一个与 fd 关联的设备描述字符，否则返回 `None`。

`os.``dup`(fd)

  返回一个文件描述符 fd 的副本。该文件描述符的副本是 不可继承的。

  在 Windows 中，当复制一个标准流（0: stdin, 1: stdout, 2: stderr）时，新的文件描述符是 可继承的。

  3.4 版更變: 新的文件描述符现在是不可继承的。

`os.``dup2`(fd, fd2, inheritable=True)

  把文件描述符 fd 复制为 fd2，必要时先关闭后者。返回 fd2。新的文件描述符默认是 可继承的，除非在 inheritable 为 `False` 时，是不可继承的。

  3.4 版更變: 添加可选参数 inheritable。

  3.7 版更變: 成功时返回 fd2，以过去的版本中，总是返回 `None`。

`os.``fchmod`(fd, mode)

  将 fd 指定文件的权限状态修改为 mode。可以参考 `chmod()` 中列出 mode 的可用值。从Python 3.3开始，这相当于 `os.chmod(fd, mode)`。

  可用性: Unix。

`os.``fchown`(fd, uid, gid)

  分别将 fd 指定文件的所有者和组 ID 修改为 uid 和 gid 的值。若不想变更其中的某个 ID，可将相应值设为 -1。参考 `chown()`。从 Python 3.3 开始，这相当于 `os.chown(fd, uid, gid)`。

  可用性: Unix。

`os.``fdatasync`(fd)

  强制将文件描述符 fd 指定文件写入磁盘。不强制更新元数据。

  可用性: Unix。

  備註

  该功能在 MacOS 中不可用。

`os.``fpathconf`(fd, name)

  返回与打开的文件有关的系统配置信息。name 指定要查找的配置名称，它可以是字符串，是一个系统已定义的名称，这些名称定义在不同标准（POSIX.1，Unix 95，Unix 98 等）中。一些平台还定义了额外的其他名称。当前操作系统已定义的名称在 `pathconf_names` 字典中给出。对于未包含在该映射中的配置名称，也可以传递一个整数作为 name。

  如果 name 是一个字符串且不是已定义的名称，将抛出 `ValueError` 异常。如果当前系统不支持 name 指定的配置名称，即使该名称存在于 `pathconf_names`，也会抛出 `OSError` 异常，错误码为 `errno.EINVAL`。

  从 Python 3.3 起，此功能等价于 `os.pathconf(fd, name)`。

  可用性: Unix。

`os.``fstat`(fd)

  获取文件描述符 fd 的状态. 返回一个 `stat_result` 对象。

  从 Python 3.3 起，此功能等价于 `os.stat(fd)`。

  也參考

  `stat()` 函数。

`os.``fstatvfs`(fd)

  返回文件系统的信息，该文件系统是文件描述符 fd 指向的文件所在的文件系统，与 `statvfs()` 一样。从 Python 3.3 开始，它等效于 `os.statvfs(fd)`。

  可用性: Unix。

`os.``fsync`(fd)

  强制将文件描述符 fd 指向的文件写入磁盘。在 Unix，这将调用原生 `fsync()` 函数；在 Windows，则是 MS `_commit()` 函数。

  如果要写入的是缓冲区内的 Python 文件对象 f，请先执行 `f.flush()`，然后执行 `os.fsync(f.fileno())`，以确保与 f 关联的所有内部缓冲区都写入磁盘。

  可用性: Unix, Windows。

`os.``ftruncate`(fd, length)

  将文件描述符 fd 指向的文件切分开，以使其最大为 length 字节。从 Python 3.3 开始，它等效于 `os.truncate(fd, length)`。

  引发一个 审核事件 `os.truncate` 附带参数 `fd`, `length`。

  可用性: Unix, Windows。

  3.5 版更變: 添加了 Windows 支持

`os.``get_blocking`(fd)

  获取文件描述符的阻塞模式：如果设置了 `O_NONBLOCK` 标志位，返回 `False`，如果该标志位被清除，返回 `True`。

  参见 `set_blocking()` 和 `socket.socket.setblocking()`。

  可用性: Unix。

  3.5 版新加入.

`os.``isatty`(fd)

  如果文件描述符 fd 打开且已连接至 tty 设备（或类 tty 设备），返回 `True`，否则返回 `False`。

`os.``lockf`(fd, cmd, len)

  在打开的文件描述符上，使用、测试或删除 POSIX 锁。fd 是一个打开的文件描述符。cmd 指定要进行的操作，它们是 `F_LOCK`、`F_TLOCK`、`F_ULOCK` 或 `F_TEST` 中的一个。len 指定哪部分文件需要锁定。

  可用性: Unix。

  3.3 版新加入.

`os.``F_LOCK`
`os.``F_TLOCK`
`os.``F_ULOCK`
`os.``F_TEST`

  标志位，用于指定 `lockf()` 进行哪一种操作。

  可用性: Unix。

  3.3 版新加入.

`os.``lseek`(fd, pos, how)

  将文件描述符 fd 的当前位置设置为 pos，位置的计算方式 how 如下：设置为 `SEEK_SET` 或 `0` 表示从文件开头计算，设置为 `SEEK_CUR` 或 `1` 表示从文件当前位置计算，设置为 `SEEK_END` 或 `2` 表示文件末尾计算。返回新指针位置，这个位置是从文件开头计算的，单位是字节。

`os.``SEEK_SET`
`os.``SEEK_CUR`
`os.``SEEK_END`

  `lseek()` 函数的参数，它们的值分别为 0、1 和 2。

  3.3 版新加入: 某些操作系统可能支持其他值，例如 `os.SEEK_HOLE` 或 `os.SEEK_DATA`。

`os.``open`(path, flags, mode=0o777, *, dir_fd=None)

  打开文件 path，根据 flags 设置各种标志位，并根据 mode 设置其权限模式。当计算 mode 时，会首先根据当前 umask 值将部分权限去除。本方法返回新文件的描述符。新的文件描述符是 不可继承 的。

  有关 flag 和 mode 取值的说明，请参见 C 运行时文档。标志位常量（如 `O_RDONLY` 和 `O_WRONLY`）在 `os` 模块中定义。特别地，在 Windows 上需要添加 `O_BINARY` 才能以二进制模式打开文件。

  本函数带有 dir_fd 参数，支持 基于目录描述符的相对路径。

  引发一个 审核事件 `open` 附带参数 `path`、`mode`、`flags`。

  3.4 版更變: 新的文件描述符现在是不可继承的。

  備註

  本函数适用于底层的 I/O。常规用途请使用内置函数 `open()`，该函数的 `read()` 和 `write()` 方法（及其他方法）会返回 文件对象。要将文件描述符包装在文件对象中，请使用 `fdopen()`。

  3.3 版新加入: dir_fd 参数。

  3.5 版更變: 如果系统调用被中断，但信号处理程序没有触发异常，此函数现在会重试系统调用，而不是触发 `InterruptedError` 异常 (原因详见 PEP 475)。

  3.6 版更變: 接受一个 类路径对象。

以下常量是 `open()` 函数 flags 参数的选项。可以用按位或运算符 `|` 将它们组合使用。部分常量并非在所有平台上都可用。有关其可用性和用法的说明，请参阅 open(2) 手册（Unix 上）或 MSDN （Windows 上）。

`os.``O_RDONLY`
`os.``O_WRONLY`
`os.``O_RDWR`
`os.``O_APPEND`
`os.``O_CREAT`
`os.``O_EXCL`
`os.``O_TRUNC`

  上述常量在 Unix 和 Windows 上均可用。

`os.``O_DSYNC`
`os.``O_RSYNC`
`os.``O_SYNC`
`os.``O_NDELAY`
`os.``O_NONBLOCK`
`os.``O_NOCTTY`
`os.``O_CLOEXEC`

  这个常数仅在 Unix 系统中可用。

  3.3 版更變: 增加 `O_CLOEXEC` 常量。

`os.``O_BINARY`
`os.``O_NOINHERIT`
`os.``O_SHORT_LIVED`
`os.``O_TEMPORARY`
`os.``O_RANDOM`
`os.``O_SEQUENTIAL`
`os.``O_TEXT`

  这个常数仅在 Windows 系统中可用。

`os.``O_ASYNC`
`os.``O_DIRECT`
`os.``O_DIRECTORY`
`os.``O_NOFOLLOW`
`os.``O_NOATIME`
`os.``O_PATH`
`os.``O_TMPFILE`
`os.``O_SHLOCK`
`os.``O_EXLOCK`

  上述常量是扩展常量，如果 C 库未定义它们，则不存在。

  3.4 版更變: 在支持的系统上增加 `O_PATH`。增加 `O_TMPFILE`，仅在 Linux Kernel 3.11 或更高版本可用。

`os.``openpty`()

  打开一对新的伪终端，返回一对文件描述符``（主，从）``，分别为 pty 和 tty。新的文件描述符是 不可继承 的。对于（稍微）轻量一些的方法，请使用 `pty` 模块。

  可用性: 某些 Unix。

  3.4 版更變: 新的文件描述符不再可继承。

`os.``pipe`()

  创建一个管道，返回一对分别用于读取和写入的文件描述符 `(r, w)`。新的文件描述符是 不可继承 的。

  可用性: Unix, Windows。

  3.4 版更變: 新的文件描述符不再可继承。

`os.``pipe2`(flags)

  创建带有 flags 标志位的管道。可通过对以下一个或多个值进行“或”运算来构造这些 flags：`O_NONBLOCK`、`O_CLOEXEC`。返回一对分别用于读取和写入的文件描述符 `(r, w)`。

  可用性: 某些 Unix。

  3.3 版新加入.

`os.``posix_fallocate`(fd, offset, len)

  确保为 fd 指向的文件分配了足够的磁盘空间，该空间从偏移量 offset 开始，到 len 字节为止。

  可用性: Unix。

  3.3 版新加入.

`os.``posix_fadvise`(fd, offset, len, advice)

  声明即将以特定模式访问数据，使内核可以提前进行优化。数据范围是从 fd 所指向文件的 offset 开始，持续 len 个字节。advice 的取值是如下之一：`POSIX_FADV_NORMAL`, `POSIX_FADV_SEQUENTIAL`, `POSIX_FADV_RANDOM`, `POSIX_FADV_NOREUSE`, `POSIX_FADV_WILLNEED` 或 `POSIX_FADV_DONTNEED`。

  可用性: Unix。

  3.3 版新加入.

`os.``POSIX_FADV_NORMAL`
`os.``POSIX_FADV_SEQUENTIAL`
`os.``POSIX_FADV_RANDOM`
`os.``POSIX_FADV_NOREUSE`
`os.``POSIX_FADV_WILLNEED`
`os.``POSIX_FADV_DONTNEED`

  用于 `posix_fadvise()` 的 advice 参数的标志位，指定可能使用的访问模式。

  可用性: Unix。

  3.3 版新加入.

`os.``pread`(fd, n, offset)

  从文件描述符 fd 所指向文件的偏移位置 offset 开始，读取至多 n 个字节，而保持文件偏移量不变。

  返回所读取字节的字节串 (bytestring)。如果到达了 fd 指向的文件末尾，则返回空字节对象。

  可用性: Unix。

  3.3 版新加入.

`os.``preadv`(fd, buffers, offset, flags=0)

  从文件描述符 fd 所指向文件的偏移位置 offset 开始，将数据读取至可变 字节类对象 缓冲区 buffers 中，保持文件偏移量不变。将数据依次存放到每个缓冲区中，填满一个后继续存放到序列中的下一个缓冲区，来保存其余数据。

  flags 参数可以由零个或多个标志位进行按位或运算来得到：

  - `RWF_HIPRI`

  - `RWF_NOWAIT`

  返回实际读取的字节总数，该总数可以小于所有对象的总容量。

  操作系统可能对允许使用的缓冲区数量有限制（使用 `sysconf()` 获取 `'SC_IOV_MAX'` 值）。

  本方法结合了 `os.readv()` 和 `os.pread()` 的功能。

  可用性：Linux 2.6.30 或更高版本，FreeBSD 6.0 或更高版本，OpenBSD 2.7 或更高版本。使用标志位需要 Linux 4.6 或更高版本。

  3.7 版新加入.

`os.``RWF_NOWAIT`

  不要等待无法立即获得的数据。如果指定了此标志，那么当需要从后备存储器中读取数据，或等待文件锁时，系统调用将立即返回。

  如果成功读取数据，则返回读取的字节数。如果未读取到数据，则返回 `-1`，并将错误码 errno 置为 `errno.EAGAIN`。

  可用性：Linux 4.14 或更高版本。

  3.7 版新加入.

`os.``RWF_HIPRI`

  高优先级读/写。允许基于块的文件系统对设备进行轮询，这样可以降低延迟，但可能会占用更多资源。

  目前在 Linux 上，此功能仅在使用 `O_DIRECT` 标志打开的文件描述符上可用。

  可用性：Linux 4.6 或更高版本。

  3.7 版新加入.

`os.``pwrite`(fd, str, offset)

  将 str 中的字节串 (bytestring) 写入文件描述符 fd 的偏移位置 offset 处，保持文件偏移量不变。

  返回实际写入的字节数。

  可用性: Unix。

  3.3 版新加入.

`os.``pwritev`(fd, buffers, offset, flags=0)

  将缓冲区 buffers 的内容写入文件描述符 fd 的偏移位置 offset 处，保持文件偏移量不变。缓冲区 buffers 必须是由 字节类对象 组成的序列。缓冲区以数组顺序处理。先写入第一个缓冲区的全部内容，再写入第二个缓冲区，照此继续。

  flags 参数可以由零个或多个标志位进行按位或运算来得到：

  - `RWF_DSYNC`

  - `RWF_SYNC`

  返回实际写入的字节总数。

  操作系统可能对允许使用的缓冲区数量有限制（使用 `sysconf()` 获取 `'SC_IOV_MAX'` 值）。

  本方法结合了 `os.writev()` 和 `os.pwrite()` 的功能。

  可用性：Linux 2.6.30 或更高版本，FreeBSD 6.0 或更高版本，OpenBSD 2.7 或更高版本。使用标志位需要 Linux 4.7 或更高版本。

  3.7 版新加入.

`os.``RWF_DSYNC`

  提供立即写入功能，等效于 `O_DSYNC` `open(2)` 标志。该标志仅作用于系统调用写入的数据。

  可用性：Linux 4.7 或更高版本。

  3.7 版新加入.

`os.``RWF_SYNC`

  提供立即写入功能，等效于 `O_SYNC` `open(2)` 标志。该标志仅作用于系统调用写入的数据。

  可用性：Linux 4.7 或更高版本。

  3.7 版新加入.

`os.``read`(fd, n)

  从文件描述符 fd 中读取至多 n 个字节。

  返回所读取字节的字节串 (bytestring)。如果到达了 fd 指向的文件末尾，则返回空字节对象。

  備註

  该功能适用于低级 I/O 操作，必须用于 `os.open()` 或 `pipe()` 返回的文件描述符。若要读取由内建函数 `open()`、`popen()`、`fdopen()` 或 `sys.stdin` 返回的 "文件对象"，则应使用其相应的 `read()` 或 `readline()` 方法。

  3.5 版更變: 如果系统调用被中断，但信号处理程序没有触发异常，此函数现在会重试系统调用，而不是触发 `InterruptedError` 异常 (原因详见 PEP 475)。

`os.``sendfile`(out, in, offset, count)
`os.``sendfile`(out, in, offset, count, [headers, ][trailers, ]flags=0)

  将文件描述符 in 中的 count 字节复制到文件描述符 out 的偏移位置 offset 处。返回复制的字节数，如果到达 EOF，返回 0。

  定义了 `sendfile()` 的所有平台均支持第一种函数用法。

  在 Linux 上，将 offset 设置为 `None`，则从 in 的当前位置开始读取，并更新 in 的位置。

  第二种函数用法可以在 Mac OS X 和 FreeBSD 上使用，其中，headers 和 trailers 是任意的缓冲区序列，它们分别在写入 in 的数据前、后被写入。返回值与第一种用法相同。

  在 Mac OS X 和 FreeBSD 上，将 count 设为 0 表示持续复制直到 in 的结尾。

  所有平台都支持将套接字作为 out 文件描述符，有些平台也支持其他类型（如常规文件或管道）。

  跨平台应用程序不应使用 headers、trailers 和 flags 参数。

  可用性: Unix。

  備註

  有关 `sendfile()` 的高级封装，参见 `socket.socket.sendfile()`。

  3.3 版新加入.

`os.``set_blocking`(fd, blocking)

  设置指定文件描述符的阻塞模式：如果 blocking 为 `False`，则为该描述符设置 `O_NONBLOCK` 标志位，反之则清除该标志位。

  参见 `get_blocking()` 和 `socket.socket.setblocking()`。

  可用性: Unix。

  3.5 版新加入.

`os.``SF_NODISKIO`
`os.``SF_MNOWAIT`
`os.``SF_SYNC`

  `sendfile()` 函数的参数（假设当前实现支持这些参数）。

  可用性: Unix。

  3.3 版新加入.

`os.``readv`(fd, buffers)

  从文件描述符 fd 将数据读取至多个可变的 字节类对象 缓冲区 buffers 中。将数据依次存放到每个缓冲区中，填满一个后继续存放到序列中的下一个缓冲区，来保存其余数据。

  返回实际读取的字节总数，该总数可以小于所有对象的总容量。

  操作系统可能对允许使用的缓冲区数量有限制（使用 `sysconf()` 获取 `'SC_IOV_MAX'` 值）。

  可用性: Unix。

  3.3 版新加入.

`os.``tcgetpgrp`(fd)

  返回与 fd 指定的终端相关联的进程组（fd 是由 `os.open()` 返回的已打开的文件描述符）。

  可用性: Unix。

`os.``tcsetpgrp`(fd, pg)

  设置与 fd 指定的终端相关联的进程组为 pg*（*fd 是由 `os.open()` 返回的已打开的文件描述符）。

  可用性: Unix。

`os.``ttyname`(fd)

  返回一个字符串，该字符串表示与文件描述符 fd 关联的终端。如果 fd 没有与终端关联，则抛出异常。

  可用性: Unix。

`os.``write`(fd, str)

  将 str 中的字节串 (bytestring) 写入文件描述符 fd。

  返回实际写入的字节数。

  備註

  该功能适用于低级 I/O 操作，必须用于 `os.open()` 或 `pipe()` 返回的文件描述符。若要写入由内建函数 `open()`、`popen()`、`fdopen()`、`sys.stdout` 或 `sys.stderr` 返回的 "文件对象"，则应使用其相应的 `write()` 方法。

  3.5 版更變: 如果系统调用被中断，但信号处理程序没有触发异常，此函数现在会重试系统调用，而不是触发 `InterruptedError` 异常 (原因详见 PEP 475)。

`os.``writev`(fd, buffers)

  将缓冲区 buffers 的内容写入文件描述符 fd。缓冲区 buffers 必须是由 字节类对象 组成的序列。缓冲区以数组顺序处理。先写入第一个缓冲区的全部内容，再写入第二个缓冲区，照此继续。

  返回实际写入的字节总数。

  操作系统可能对允许使用的缓冲区数量有限制（使用 `sysconf()` 获取 `'SC_IOV_MAX'` 值）。

  可用性: Unix。

  3.3 版新加入.

### 查询终端的尺寸

3.3 版新加入.

`os.``get_terminal_size`(fd=STDOUT_FILENO)

  返回终端窗口的尺寸，格式为 `(columns, lines)`，它是类型为 `terminal_size` 的元组。

  可选参数 `fd``（默认为 ``STDOUT_FILENO` 或标准输出）指定应查询的文件描述符。

  如果文件描述符未连接到终端，则抛出 `OSError` 异常。

  `shutil.get_terminal_size()` 是供常规使用的高阶函数，`os.get_terminal_size` 是其底层的实现。

  可用性: Unix, Windows。

class `os.``terminal_size`

  元组的子类，存储终端窗口尺寸 `(columns, lines)`。

  `columns`

    终端窗口的宽度，单位为字符。

  `lines`

    终端窗口的高度，单位为字符。

### 文件描述符的继承

3.4 版新加入.

每个文件描述符都有一个 "inheritable"（可继承）标志位，该标志位控制了文件描述符是否可以由子进程继承。从 Python 3.4 开始，由 Python 创建的文件描述符默认是不可继承的。

在 UNIX 上，执行新程序时，不可继承的文件描述符在子进程中是关闭的，其他文件描述符将被继承。

在 Windows 上，不可继承的句柄和文件描述符在子进程中是关闭的，但标准流（文件描述符 0、1 和 2 即标准输入、标准输出和标准错误）是始终继承的。如果使用 `spawn*` 函数，所有可继承的句柄和文件描述符都将被继承。如果使用 `subprocess` 模块，将关闭除标准流以外的所有文件描述符，并且仅当 close_fds 参数为 `False` 时才继承可继承的句柄。

`os.``get_inheritable`(fd)

  获取指定文件描述符的“可继承”标志位（为布尔值）。

`os.``set_inheritable`(fd, inheritable)

  设置指定文件描述符的“可继承”标志位。

`os.``get_handle_inheritable`(handle)

  获取指定句柄的“可继承”标志位（为布尔值）。

  可用性: Windows。

`os.``set_handle_inheritable`(handle, inheritable)

  设置指定句柄的“可继承”标志位。

  可用性: Windows。

## 文件和目录

在某些 Unix 平台上，许多函数支持以下一项或多项功能：

- 指定文件描述符为参数： 通常在 `os` 模块中提供给函数的 path 参数必须是表示文件路径的字符串，但是，某些函数现在可以接受其 path 参数为打开文件描述符，该函数将对描述符指向的文件进行操作。（对于 POSIX 系统，Python 将调用以 `f` 开头的函数变体（如调用 `fchdir` 而不是 `chdir`）。）

  可以用 `os.supports_fd` 检查某个函数在你的平台上是否支持将 path 参数指定为文件描述符。如果不支持，使用该功能将抛出 `NotImplementedError` 异常。

  如果该函数还支持 dir_fd 或 follow_symlinks 参数，那么用文件描述符作为 path 后就不能再指定上述参数了。

- 基于目录描述符的相对路径： 如果 dir_fd 不是 `None`，它就应该是一个指向目录的文件描述符，这时待操作的 path 应该是相对路径，相对路径是相对于前述目录的。如果 path 是绝对路径，则 dir_fd 将被忽略。（对于 POSIX 系统，Python 将调用该函数的变体，变体以 `at` 结尾，可能以 `f` 开头（如调用 `faccessat` 而不是 `access`）。

  可以用 `os.supports_dir_fd` 检查某个函数在你的平台上是否支持 dir_fd。如果不支持，使用该功能将抛出 `NotImplementedError` 异常。

- 不跟踪符号链接： 如果 follow_symlinks 为 `False`，并且待操作路径的最后一个元素是符号链接，则该函数将在符号链接本身而不是链接所指向的文件上操作。（对于 POSIX 系统，Python 将调用该函数的 `l...` 变体。）

  可以用 `os.supports_follow_symlinks` 检查某个函数在你的平台上是否支持 follow_symlinks。如果不支持，使用该功能将抛出 `NotImplementedError` 异常。

`os.``access`(path, mode, *, dir_fd=None, effective_ids=False, follow_symlinks=True)

  使用 实际用户ID/用户组ID 测试对 path 的访问。请注意，大多数测试操作将使用 有效用户ID/用户组ID，因此可以在 suid/sgid 环境中运用此例程，来测试调用用户是否具有对 path 的指定访问权限。mode 为 `F_OK` 时用于测试 path 是否存在，也可以对 `R_OK`、`W_OK` 和 `X_OK` 中的一个或多个进行“或”运算来测试指定权限。允许访问则返回 `True`，否则返回 `False`。更多信息请参见 Unix 手册页 access(2)。

  本函数支持指定 基于目录描述符的相对路径 和 不跟踪符号链接。

  如果 effective_ids 为 `True`，`access()` 将使用 有效用户ID/用户组ID 而非 实际用户ID/用户组ID 进行访问检查。您的平台可能不支持 effective_ids，您可以使用 `os.supports_effective_ids` 检查它是否可用。如果不可用，使用它时会抛出 `NotImplementedError` 异常。

  備註

  Using `access()` to check if a user is authorized to e.g. open a file before actually doing so using `open()` creates a security hole, because the user might exploit the short time interval between checking and opening the file to manipulate it. It's preferable to use EAFP techniques. For example:

      if os.access("myfile", os.R_OK):
          with open("myfile") as fp:
              return fp.read()
      return "some default data"

  最好写成:

      try:
          fp = open("myfile")
      except PermissionError:
          return "some default data"
      else:
          with fp:
              return fp.read()

  備註

  I/O operations may fail even when `access()` indicates that they would succeed, particularly for operations on network filesystems which may have permissions semantics beyond the usual POSIX permission-bit model.

  3.3 版更變: Added the dir_fd, effective_ids, and follow_symlinks parameters.

  3.6 版更變: 接受一个 类路径对象。

`os.``F_OK`
`os.``R_OK`
`os.``W_OK`
`os.``X_OK`

  Values to pass as the mode parameter of `access()` to test the existence, readability, writability and executability of path, respectively.

`os.``chdir`(path)

  Change the current working directory to path.

  This function can support specifying a file descriptor. The descriptor must refer to an opened directory, not an open file.

  This function can raise `OSError` and subclasses such as `FileNotFoundError`, `PermissionError`, and `NotADirectoryError`.

  3.3 版新加入: Added support for specifying path as a file descriptor on some platforms.

  3.6 版更變: 接受一个 类路径对象。

`os.``chflags`(path, flags, *, follow_symlinks=True)

  Set the flags of path to the numeric flags. flags may take a combination (bitwise OR) of the following values (as defined in the `stat` module):

  - `stat.UF_NODUMP`

  - `stat.UF_IMMUTABLE`

  - `stat.UF_APPEND`

  - `stat.UF_OPAQUE`

  - `stat.UF_NOUNLINK`

  - `stat.UF_COMPRESSED`

  - `stat.UF_HIDDEN`

  - `stat.SF_ARCHIVED`

  - `stat.SF_IMMUTABLE`

  - `stat.SF_APPEND`

  - `stat.SF_NOUNLINK`

  - `stat.SF_SNAPSHOT`

  This function can support not following symlinks.

  可用性: Unix。

  3.3 版新加入: The follow_symlinks argument.

  3.6 版更變: 接受一个 类路径对象。

`os.``chmod`(path, mode, *, dir_fd=None, follow_symlinks=True)

  Change the mode of path to the numeric mode. mode may take one of the following values (as defined in the `stat` module) or bitwise ORed combinations of them:

  - `stat.S_ISUID`

  - `stat.S_ISGID`

  - `stat.S_ENFMT`

  - `stat.S_ISVTX`

  - `stat.S_IREAD`

  - `stat.S_IWRITE`

  - `stat.S_IEXEC`

  - `stat.S_IRWXU`

  - `stat.S_IRUSR`

  - `stat.S_IWUSR`

  - `stat.S_IXUSR`

  - `stat.S_IRWXG`

  - `stat.S_IRGRP`

  - `stat.S_IWGRP`

  - `stat.S_IXGRP`

  - `stat.S_IRWXO`

  - `stat.S_IROTH`

  - `stat.S_IWOTH`

  - `stat.S_IXOTH`

  This function can support specifying a file descriptor, paths relative to directory descriptors and not following symlinks.

  備註

  Although Windows supports `chmod()`, you can only set the file's read-only flag with it (via the `stat.S_IWRITE` and `stat.S_IREAD` constants or a corresponding integer value). All other bits are ignored.

  3.3 版新加入: Added support for specifying path as an open file descriptor, and the dir_fd and follow_symlinks arguments.

  3.6 版更變: 接受一个 类路径对象。

`os.``chown`(path, uid, gid, *, dir_fd=None, follow_symlinks=True)

  Change the owner and group id of path to the numeric uid and gid. To leave one of the ids unchanged, set it to -1.

  This function can support specifying a file descriptor, paths relative to directory descriptors and not following symlinks.

  See `shutil.chown()` for a higher-level function that accepts names in addition to numeric ids.

  可用性: Unix。

  3.3 版新加入: Added support for specifying path as an open file descriptor, and the dir_fd and follow_symlinks arguments.

  3.6 版更變: Supports a path-like object.

`os.``chroot`(path)

  Change the root directory of the current process to path.

  可用性: Unix。

  3.6 版更變: 接受一个 类路径对象。

`os.``fchdir`(fd)

  Change the current working directory to the directory represented by the file descriptor fd. The descriptor must refer to an opened directory, not an open file. As of Python 3.3, this is equivalent to `os.chdir(fd)`.

  可用性: Unix。

`os.``getcwd`()

  Return a string representing the current working directory.

`os.``getcwdb`()

  Return a bytestring representing the current working directory.

  3.8 版更變: The function now uses the UTF-8 encoding on Windows, rather than the ANSI code page: see PEP 529 for the rationale. The function is no longer deprecated on Windows.

`os.``lchflags`(path, flags)

  Set the flags of path to the numeric flags, like `chflags()`, but do not follow symbolic links. As of Python 3.3, this is equivalent to `os.chflags(path, flags, follow_symlinks=False)`.

  可用性: Unix。

  3.6 版更變: 接受一个 类路径对象。

`os.``lchmod`(path, mode)

  Change the mode of path to the numeric mode. If path is a symlink, this affects the symlink rather than the target. See the docs for `chmod()` for possible values of mode. As of Python 3.3, this is equivalent to `os.chmod(path, mode, follow_symlinks=False)`.

  可用性: Unix。

  3.6 版更變: 接受一个 类路径对象。

`os.``lchown`(path, uid, gid)

  Change the owner and group id of path to the numeric uid and gid. This function will not follow symbolic links. As of Python 3.3, this is equivalent to `os.chown(path, uid, gid, follow_symlinks=False)`.

  可用性: Unix。

  3.6 版更變: 接受一个 类路径对象。

`os.``link`(src, dst, *, src_dir_fd=None, dst_dir_fd=None, follow_symlinks=True)

  Create a hard link pointing to src named dst.

  This function can support specifying src_dir_fd and/or dst_dir_fd to supply paths relative to directory descriptors, and not following symlinks.

  可用性: Unix, Windows。

  3.2 版更變: 添加了Windows 支持

  3.3 版新加入: Added the src_dir_fd, dst_dir_fd, and follow_symlinks arguments.

  3.6 版更變: Accepts a path-like object for src and dst.

`os.``listdir`(path='.')

  Return a list containing the names of the entries in the directory given by path. The list is in arbitrary order, and does not include the special entries `'.'` and `'..'` even if they are present in the directory.

  path may be a path-like object. If path is of type `bytes` (directly or indirectly through the `PathLike` interface), the filenames returned will also be of type `bytes`; in all other circumstances, they will be of type `str`.

  This function can also support specifying a file descriptor; the file descriptor must refer to a directory.

  Raises an auditing event `os.listdir` with argument `path`.

  備註

  To encode `str` filenames to `bytes`, use `fsencode()`.

  也參考

  The `scandir()` function returns directory entries along with file attribute information, giving better performance for many common use cases.

  3.2 版更變: The path parameter became optional.

  3.3 版新加入: Added support for specifying path as an open file descriptor.

  3.6 版更變: 接受一个 类路径对象。

`os.``lstat`(path, *, dir_fd=None)

  Perform the equivalent of an `lstat()` system call on the given path. Similar to `stat()`, but does not follow symbolic links. Return a `stat_result` object.

  On platforms that do not support symbolic links, this is an alias for `stat()`.

  As of Python 3.3, this is equivalent to `os.stat(path, dir_fd=dir_fd, follow_symlinks=False)`.

  This function can also support paths relative to directory descriptors.

  也參考

  `stat()` 函数。

  3.2 版更變: Added support for Windows 6.0 (Vista) symbolic links.

  3.3 版更變: Added the dir_fd parameter.

  3.6 版更變: Accepts a path-like object for src and dst.

  3.8 版更變: On Windows, now opens reparse points that represent another path (name surrogates), including symbolic links and directory junctions. Other kinds of reparse points are resolved by the operating system as for `stat()`.

`os.``mkdir`(path, mode=0o777, *, dir_fd=None)

  Create a directory named path with numeric mode mode.

  If the directory already exists, `FileExistsError` is raised.

  On some systems, mode is ignored. Where it is used, the current umask value is first masked out. If bits other than the last 9 (i.e. the last 3 digits of the octal representation of the mode) are set, their meaning is platform-dependent. On some platforms, they are ignored and you should call `chmod()` explicitly to set them.

  This function can also support paths relative to directory descriptors.

  It is also possible to create temporary directories; see the `tempfile` module's `tempfile.mkdtemp()` function.

  3.3 版新加入: dir_fd 参数。

  3.6 版更變: 接受一个 类路径对象。

`os.``makedirs`(name, mode=0o777, exist_ok=False)

  Recursive directory creation function. Like `mkdir()`, but makes all intermediate-level directories needed to contain the leaf directory.

  The mode parameter is passed to `mkdir()` for creating the leaf directory; see the mkdir() description for how it is interpreted. To set the file permission bits of any newly-created parent directories you can set the umask before invoking `makedirs()`. The file permission bits of existing parent directories are not changed.

  If exist_ok is `False` (the default), an `FileExistsError` is raised if the target directory already exists.

  備註

  `makedirs()` will become confused if the path elements to create include `pardir` (eg. ".." on UNIX systems).

  This function handles UNC paths correctly.

  3.2 版新加入: The exist_ok parameter.

  3.4.1 版更變: Before Python 3.4.1, if exist_ok was `True` and the directory existed, `makedirs()` would still raise an error if mode did not match the mode of the existing directory. Since this behavior was impossible to implement safely, it was removed in Python 3.4.1. See bpo-21082.

  3.6 版更變: 接受一个 类路径对象。

  3.7 版更變: The mode argument no longer affects the file permission bits of newly-created intermediate-level directories.

`os.``mkfifo`(path, mode=0o666, *, dir_fd=None)

  Create a FIFO (a named pipe) named path with numeric mode mode. The current umask value is first masked out from the mode.

  This function can also support paths relative to directory descriptors.

  FIFOs are pipes that can be accessed like regular files. FIFOs exist until they are deleted (for example with `os.unlink()`). Generally, FIFOs are used as rendezvous between "client" and "server" type processes: the server opens the FIFO for reading, and the client opens it for writing. Note that `mkfifo()` doesn't open the FIFO --- it just creates the rendezvous point.

  可用性: Unix。

  3.3 版新加入: dir_fd 参数。

  3.6 版更變: 接受一个 类路径对象。

`os.``mknod`(path, mode=0o600, device=0, *, dir_fd=None)

  Create a filesystem node (file, device special file or named pipe) named path. mode specifies both the permissions to use and the type of node to be created, being combined (bitwise OR) with one of `stat.S_IFREG`, `stat.S_IFCHR`, `stat.S_IFBLK`, and `stat.S_IFIFO` (those constants are available in `stat`). For `stat.S_IFCHR` and `stat.S_IFBLK`, device defines the newly created device special file (probably using `os.makedev()`), otherwise it is ignored.

  This function can also support paths relative to directory descriptors.

  可用性: Unix。

  3.3 版新加入: dir_fd 参数。

  3.6 版更變: 接受一个 类路径对象。

`os.``major`(device)

  Extract the device major number from a raw device number (usually the `st_dev` or `st_rdev` field from `stat`).

`os.``minor`(device)

  Extract the device minor number from a raw device number (usually the `st_dev` or `st_rdev` field from `stat`).

`os.``makedev`(major, minor)

  Compose a raw device number from the major and minor device numbers.

`os.``pathconf`(path, name)

  Return system configuration information relevant to a named file. name specifies the configuration value to retrieve; it may be a string which is the name of a defined system value; these names are specified in a number of standards (POSIX.1, Unix 95, Unix 98, and others). Some platforms define additional names as well. The names known to the host operating system are given in the `pathconf_names` dictionary. For configuration variables not included in that mapping, passing an integer for name is also accepted.

  如果 name 是一个字符串且不是已定义的名称，将抛出 `ValueError` 异常。如果当前系统不支持 name 指定的配置名称，即使该名称存在于 `pathconf_names`，也会抛出 `OSError` 异常，错误码为 `errno.EINVAL`。

  This function can support specifying a file descriptor.

  可用性: Unix。

  3.6 版更變: 接受一个 类路径对象。

`os.``pathconf_names`

  Dictionary mapping names accepted by `pathconf()` and `fpathconf()` to the integer values defined for those names by the host operating system. This can be used to determine the set of names known to the system.

  可用性: Unix。

`os.``readlink`(path, *, dir_fd=None)

  Return a string representing the path to which the symbolic link points. The result may be either an absolute or relative pathname; if it is relative, it may be converted to an absolute pathname using `os.path.join(os.path.dirname(path), result)`.

  If the path is a string object (directly or indirectly through a `PathLike` interface), the result will also be a string object, and the call may raise a UnicodeDecodeError. If the path is a bytes object (direct or indirectly), the result will be a bytes object.

  This function can also support paths relative to directory descriptors.

  When trying to resolve a path that may contain links, use `realpath()` to properly handle recursion and platform differences.

  可用性: Unix, Windows。

  3.2 版更變: Added support for Windows 6.0 (Vista) symbolic links.

  3.3 版新加入: dir_fd 参数。

  3.6 版更變: Accepts a path-like object on Unix.

  3.8 版更變: Accepts a path-like object and a bytes object on Windows.

  3.8 版更變: Added support for directory junctions, and changed to return the substitution path (which typically includes `\\?\` prefix) rather than the optional "print name" field that was previously returned.

`os.``remove`(path, *, dir_fd=None)

  Remove (delete) the file path. If path is a directory, an `IsADirectoryError` is raised. Use `rmdir()` to remove directories.

  This function can support paths relative to directory descriptors.

  On Windows, attempting to remove a file that is in use causes an exception to be raised; on Unix, the directory entry is removed but the storage allocated to the file is not made available until the original file is no longer in use.

  This function is semantically identical to `unlink()`.

  3.3 版新加入: dir_fd 参数。

  3.6 版更變: 接受一个 类路径对象。

`os.``removedirs`(name)

  Remove directories recursively. Works like `rmdir()` except that, if the leaf directory is successfully removed, `removedirs()` tries to successively remove every parent directory mentioned in path until an error is raised (which is ignored, because it generally means that a parent directory is not empty). For example, `os.removedirs('foo/bar/baz')` will first remove the directory `'foo/bar/baz'`, and then remove `'foo/bar'` and `'foo'` if they are empty. Raises `OSError` if the leaf directory could not be successfully removed.

  3.6 版更變: 接受一个 类路径对象。

`os.``rename`(src, dst, *, src_dir_fd=None, dst_dir_fd=None)

  Rename the file or directory src to dst. If dst exists, the operation will fail with an `OSError` subclass in a number of cases:

  On Windows, if dst exists a `FileExistsError` is always raised.

  On Unix, if src is a file and dst is a directory or vice-versa, an `IsADirectoryError` or a `NotADirectoryError` will be raised respectively. If both are directories and dst is empty, dst will be silently replaced. If dst is a non-empty directory, an `OSError` is raised. If both are files, dst it will be replaced silently if the user has permission. The operation may fail on some Unix flavors if src and dst are on different filesystems. If successful, the renaming will be an atomic operation (this is a POSIX requirement).

  This function can support specifying src_dir_fd and/or dst_dir_fd to supply paths relative to directory descriptors.

  If you want cross-platform overwriting of the destination, use `replace()`.

  3.3 版新加入: The src_dir_fd and dst_dir_fd arguments.

  3.6 版更變: Accepts a path-like object for src and dst.

`os.``renames`(old, new)

  Recursive directory or file renaming function. 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 away using `removedirs()`.

  備註

  This function can fail with the new directory structure made if you lack permissions needed to remove the leaf directory or file.

  3.6 版更變: Accepts a path-like object for old and new.

`os.``replace`(src, dst, *, src_dir_fd=None, dst_dir_fd=None)

  Rename the file or directory src to dst. If dst is a directory, `OSError` will be raised. If dst exists and is a file, it will be replaced silently if the user has permission. The operation may fail if src and dst are on different filesystems. If successful, the renaming will be an atomic operation (this is a POSIX requirement).

  This function can support specifying src_dir_fd and/or dst_dir_fd to supply paths relative to directory descriptors.

  3.3 版新加入.

  3.6 版更變: Accepts a path-like object for src and dst.

`os.``rmdir`(path, *, dir_fd=None)

  Remove (delete) the directory path. If the directory does not exist or is not empty, an `FileNotFoundError` or an `OSError` is raised respectively. In order to remove whole directory trees, `shutil.rmtree()` can be used.

  This function can support paths relative to directory descriptors.

  3.3 版新加入: The dir_fd parameter.

  3.6 版更變: 接受一个 类路径对象。

`os.``scandir`(path='.')

  Return an iterator of `os.DirEntry` objects corresponding to the entries in the directory given by path. The entries are yielded in arbitrary order, and the special entries `'.'` and `'..'` are not included.

  Using `scandir()` instead of `listdir()` can significantly increase the performance of code that also needs file type or file attribute information, because `os.DirEntry` objects expose this information if the operating system provides it when scanning a directory. All `os.DirEntry` methods may perform a system call, but `is_dir()` and `is_file()` usually only require a system call for symbolic links; `os.DirEntry.stat()` always requires a system call on Unix but only requires one for symbolic links on Windows.

  path may be a path-like object. If path is of type `bytes` (directly or indirectly through the `PathLike` interface), the type of the `name` and `path` attributes of each `os.DirEntry` will be `bytes`; in all other circumstances, they will be of type `str`.

  This function can also support specifying a file descriptor; the file descriptor must refer to a directory.

  Raises an auditing event `os.scandir` with argument `path`.

  The `scandir()` iterator supports the context manager protocol and has the following method:

  `scandir.``close`()

    Close the iterator and free acquired resources.

    This is called automatically when the iterator is exhausted or garbage collected, or when an error happens during iterating. However it is advisable to call it explicitly or use the `with` statement.

    3.6 版新加入.

  The following example shows a simple use of `scandir()` to display all the files (excluding directories) in the given path that don't start with `'.'`. The `entry.is_file()` call will generally not make an additional system call:

      with os.scandir(path) as it:
          for entry in it:
              if not entry.name.startswith('.') and entry.is_file():
                  print(entry.name)

  備註

  On Unix-based systems, `scandir()` uses the system's opendir() and readdir() functions. On Windows, it uses the Win32 FindFirstFileW and FindNextFileW functions.

  3.5 版新加入.

  3.6 版新加入: Added support for the context manager protocol and the `close()` method. If a `scandir()` iterator is neither exhausted nor explicitly closed a `ResourceWarning` will be emitted in its destructor.

  The function accepts a path-like object.

  3.7 版更變: Added support for file descriptors on Unix.

class `os.``DirEntry`

  Object yielded by `scandir()` to expose the file path and other file attributes of a directory entry.

  `scandir()` will provide as much of this information as possible without making additional system calls. When a `stat()` or `lstat()` system call is made, the `os.DirEntry` object will cache the result.

  `os.DirEntry` instances are not intended to be stored in long-lived data structures; if you know the file metadata has changed or if a long time has elapsed since calling `scandir()`, call `os.stat(entry.path)` to fetch up-to-date information.

  Because the `os.DirEntry` methods can make operating system calls, they may also raise `OSError`. If you need very fine-grained control over errors, you can catch `OSError` when calling one of the `os.DirEntry` methods and handle as appropriate.

  To be directly usable as a path-like object, `os.DirEntry` implements the `PathLike` interface.

  Attributes and methods on a `os.DirEntry` instance are as follows:

  `name`

    The entry's base filename, relative to the `scandir()` path argument.

    The `name` attribute will be `bytes` if the `scandir()` path argument is of type `bytes` and `str` otherwise. Use `fsdecode()` to decode byte filenames.

  `path`

    The entry's full path name: equivalent to `os.path.join(scandir_path, entry.name)` where scandir_path is the `scandir()` path argument. The path is only absolute if the `scandir()` path argument was absolute. If the `scandir()` path argument was a file descriptor, the `path` attribute is the same as the `name` attribute.

    The `path` attribute will be `bytes` if the `scandir()` path argument is of type `bytes` and `str` otherwise. Use `fsdecode()` to decode byte filenames.

  `inode`()

    Return the inode number of the entry.

    The result is cached on the `os.DirEntry` object. Use `os.stat(entry.path, follow_symlinks=False).st_ino` to fetch up-to-date information.

    On the first, uncached call, a system call is required on Windows but not on Unix.

  `is_dir`(*, follow_symlinks=True)

    Return `True` if this entry is a directory or a symbolic link pointing to a directory; return `False` if the entry is or points to any other kind of file, or if it doesn't exist anymore.

    If follow_symlinks is `False`, return `True` only if this entry is a directory (without following symlinks); return `False` if the entry is any other kind of file or if it doesn't exist anymore.

    The result is cached on the `os.DirEntry` object, with a separate cache for follow_symlinks `True` and `False`. Call `os.stat()` along with `stat.S_ISDIR()` to fetch up-to-date information.

    On the first, uncached call, no system call is required in most cases. Specifically, for non-symlinks, neither Windows or Unix require a system call, except on certain Unix file systems, such as network file systems, that return `dirent.d_type == DT_UNKNOWN`. If the entry is a symlink, a system call will be required to follow the symlink unless follow_symlinks is `False`.

    This method can raise `OSError`, such as `PermissionError`, but `FileNotFoundError` is caught and not raised.

  `is_file`(*, follow_symlinks=True)

    Return `True` if this entry is a file or a symbolic link pointing to a file; return `False` if the entry is or points to a directory or other non-file entry, or if it doesn't exist anymore.

    If follow_symlinks is `False`, return `True` only if this entry is a file (without following symlinks); return `False` if the entry is a directory or other non-file entry, or if it doesn't exist anymore.

    The result is cached on the `os.DirEntry` object. Caching, system calls made, and exceptions raised are as per `is_dir()`.

  `is_symlink`()

    Return `True` if this entry is a symbolic link (even if broken); return `False` if the entry points to a directory or any kind of file, or if it doesn't exist anymore.

    The result is cached on the `os.DirEntry` object. Call `os.path.islink()` to fetch up-to-date information.

    On the first, uncached call, no system call is required in most cases. Specifically, neither Windows or Unix require a system call, except on certain Unix file systems, such as network file systems, that return `dirent.d_type == DT_UNKNOWN`.

    This method can raise `OSError`, such as `PermissionError`, but `FileNotFoundError` is caught and not raised.

  `stat`(*, follow_symlinks=True)

    Return a `stat_result` object for this entry. This method follows symbolic links by default; to stat a symbolic link add the `follow_symlinks=False` argument.

    On Unix, this method always requires a system call. On Windows, it only requires a system call if follow_symlinks is `True` and the entry is a reparse point (for example, a symbolic link or directory junction).

    On Windows, the `st_ino`, `st_dev` and `st_nlink` attributes of the `stat_result` are always set to zero. Call `os.stat()` to get these attributes.

    The result is cached on the `os.DirEntry` object, with a separate cache for follow_symlinks `True` and `False`. Call `os.stat()` to fetch up-to-date information.

  Note that there is a nice correspondence between several attributes and methods of `os.DirEntry` and of `pathlib.Path`. In particular, the `name` attribute has the same meaning, as do the `is_dir()`, `is_file()`, `is_symlink()` and `stat()` methods.

  3.5 版新加入.

  3.6 版更變: Added support for the `PathLike` interface. Added support for `bytes` paths on Windows.

`os.``stat`(path, *, dir_fd=None, follow_symlinks=True)

  Get the status of a file or a file descriptor. Perform the equivalent of a `stat()` system call on the given path. path may be specified as either a string or bytes -- directly or indirectly through the `PathLike` interface -- or as an open file descriptor. Return a `stat_result` object.

  This function normally follows symlinks; to stat a symlink add the argument `follow_symlinks=False`, or use `lstat()`.

  This function can support specifying a file descriptor and not following symlinks.

  On Windows, passing `follow_symlinks=False` will disable following all name-surrogate reparse points, which includes symlinks and directory junctions. Other types of reparse points that do not resemble links or that the operating system is unable to follow will be opened directly. When following a chain of multiple links, this may result in the original link being returned instead of the non-link that prevented full traversal. To obtain stat results for the final path in this case, use the `os.path.realpath()` function to resolve the path name as far as possible and call `lstat()` on the result. This does not apply to dangling symlinks or junction points, which will raise the usual exceptions.

  示例:

      >>> import os
      >>> statinfo = os.stat('somefile.txt')
      >>> statinfo
      os.stat_result(st_mode=33188, st_ino=7876932, st_dev=234881026,
      st_nlink=1, st_uid=501, st_gid=501, st_size=264, st_atime=1297230295,
      st_mtime=1297230027, st_ctime=1297230027)
      >>> statinfo.st_size
      264

  也參考

  `fstat()` and `lstat()` functions.

  3.3 版新加入: Added the dir_fd and follow_symlinks arguments, specifying a file descriptor instead of a path.

  3.6 版更變: 接受一个 类路径对象。

  3.8 版更變: On Windows, all reparse points that can be resolved by the operating system are now followed, and passing `follow_symlinks=False` disables following all name surrogate reparse points. If the operating system reaches a reparse point that it is not able to follow, stat now returns the information for the original path as if `follow_symlinks=False` had been specified instead of raising an error.

class `os.``stat_result`

  Object whose attributes correspond roughly to the members of the `stat` structure. It is used for the result of `os.stat()`, `os.fstat()` and `os.lstat()`.

  Attributes:

  `st_mode`

    File mode: file type and file mode bits (permissions).

  `st_ino`

    Platform dependent, but if non-zero, uniquely identifies the file for a given value of `st_dev`. Typically:

    - the inode number on Unix,

    - the file index on Windows

  `st_dev`

    Identifier of the device on which this file resides.

  `st_nlink`

    Number of hard links.

  `st_uid`

    User identifier of the file owner.

  `st_gid`

    Group identifier of the file owner.

  `st_size`

    Size of the file in bytes, if it is a regular file or a symbolic link. The size of a symbolic link is the length of the pathname it contains, without a terminating null byte.

  Timestamps:

  `st_atime`

    Time of most recent access expressed in seconds.

  `st_mtime`

    Time of most recent content modification expressed in seconds.

  `st_ctime`

    Platform dependent:

    - the time of most recent metadata change on Unix,

    - the time of creation on Windows, expressed in seconds.

  `st_atime_ns`

    Time of most recent access expressed in nanoseconds as an integer.

  `st_mtime_ns`

    Time of most recent content modification expressed in nanoseconds as an integer.

  `st_ctime_ns`

    Platform dependent:

    - the time of most recent metadata change on Unix,

    - the time of creation on Windows, expressed in nanoseconds as an integer.

  備註

  The exact meaning and resolution of the `st_atime`, `st_mtime`, and `st_ctime` attributes depend on the operating system and the file system. For example, on Windows systems using the FAT or FAT32 file systems, `st_mtime` has 2-second resolution, and `st_atime` has only 1-day resolution. See your operating system documentation for details.

  Similarly, although `st_atime_ns`, `st_mtime_ns`, and `st_ctime_ns` are always expressed in nanoseconds, many systems do not provide nanosecond precision. On systems that do provide nanosecond precision, the floating-point object used to store `st_atime`, `st_mtime`, and `st_ctime` cannot preserve all of it, and as such will be slightly inexact. If you need the exact timestamps you should always use `st_atime_ns`, `st_mtime_ns`, and `st_ctime_ns`.

  On some Unix systems (such as Linux), the following attributes may also be available:

  `st_blocks`

    Number of 512-byte blocks allocated for file. This may be smaller than `st_size`/512 when the file has holes.

  `st_blksize`

    "Preferred" blocksize for efficient file system I/O. Writing to a file in smaller chunks may cause an inefficient read-modify-rewrite.

  `st_rdev`

    Type of device if an inode device.

  `st_flags`

    User defined flags for file.

  On other Unix systems (such as FreeBSD), the following attributes may be available (but may be only filled out if root tries to use them):

  `st_gen`

    File generation number.

  `st_birthtime`

    Time of file creation.

  On Solaris and derivatives, the following attributes may also be available:

  `st_fstype`

    String that uniquely identifies the type of the filesystem that contains the file.

  On Mac OS systems, the following attributes may also be available:

  `st_rsize`

    Real size of the file.

  `st_creator`

    Creator of the file.

  `st_type`

    File type.

  On Windows systems, the following attributes are also available:

  `st_file_attributes`

    Windows file attributes: `dwFileAttributes` member of the `BY_HANDLE_FILE_INFORMATION` structure returned by `GetFileInformationByHandle()`. See the `FILE_ATTRIBUTE_*` constants in the `stat` module.

  `st_reparse_tag`

    When `st_file_attributes` has the `FILE_ATTRIBUTE_REPARSE_POINT` set, this field contains the tag identifying the type of reparse point. See the `IO_REPARSE_TAG_*` constants in the `stat` module.

  The standard module `stat` defines functions and constants that are useful for extracting information from a `stat` structure. (On Windows, some items are filled with dummy values.)

  For backward compatibility, a `stat_result` instance is also accessible as a tuple of at least 10 integers giving the most important (and portable) members of the `stat` structure, in the order `st_mode`, `st_ino`, `st_dev`, `st_nlink`, `st_uid`, `st_gid`, `st_size`, `st_atime`, `st_mtime`, `st_ctime`. More items may be added at the end by some implementations. For compatibility with older Python versions, accessing `stat_result` as a tuple always returns integers.

  3.3 版新加入: Added the `st_atime_ns`, `st_mtime_ns`, and `st_ctime_ns` members.

  3.5 版新加入: Added the `st_file_attributes` member on Windows.

  3.5 版更變: Windows now returns the file index as `st_ino` when available.

  3.7 版新加入: Added the `st_fstype` member to Solaris/derivatives.

  3.8 版新加入: Added the `st_reparse_tag` member on Windows.

  3.8 版更變: On Windows, the `st_mode` member now identifies special files as `S_IFCHR`, `S_IFIFO` or `S_IFBLK` as appropriate.

`os.``statvfs`(path)

  Perform a `statvfs()` system call on the given path. The return value is an object whose attributes describe the filesystem on the given path, and correspond to the members of the `statvfs` structure, namely: `f_bsize`, `f_frsize`, `f_blocks`, `f_bfree`, `f_bavail`, `f_files`, `f_ffree`, `f_favail`, `f_flag`, `f_namemax`, `f_fsid`.

  Two module-level constants are defined for the `f_flag` attribute's bit-flags: if `ST_RDONLY` is set, the filesystem is mounted read-only, and if `ST_NOSUID` is set, the semantics of setuid/setgid bits are disabled or not supported.

  Additional module-level constants are defined for GNU/glibc based systems. These are `ST_NODEV` (disallow access to device special files), `ST_NOEXEC` (disallow program execution), `ST_SYNCHRONOUS` (writes are synced at once), `ST_MANDLOCK` (allow mandatory locks on an FS), `ST_WRITE` (write on file/directory/symlink), `ST_APPEND` (append-only file), `ST_IMMUTABLE` (immutable file), `ST_NOATIME` (do not update access times), `ST_NODIRATIME` (do not update directory access times), `ST_RELATIME` (update atime relative to mtime/ctime).

  This function can support specifying a file descriptor.

  可用性: Unix。

  3.2 版更變: The `ST_RDONLY` and `ST_NOSUID` constants were added.

  3.3 版新加入: Added support for specifying path as an open file descriptor.

  3.4 版更變: The `ST_NODEV`, `ST_NOEXEC`, `ST_SYNCHRONOUS`, `ST_MANDLOCK`, `ST_WRITE`, `ST_APPEND`, `ST_IMMUTABLE`, `ST_NOATIME`, `ST_NODIRATIME`, and `ST_RELATIME` constants were added.

  3.6 版更變: 接受一个 类路径对象。

  3.7 版新加入: Added `f_fsid`.

`os.``supports_dir_fd`

  A `set` object indicating which functions in the `os` module accept an open file descriptor for their dir_fd parameter. Different platforms provide different features, and the underlying functionality Python uses to implement the dir_fd parameter is not available on all platforms Python supports. For consistency's sake, functions that may support dir_fd always allow specifying the parameter, but will throw an exception if the functionality is used when it's not locally available. (Specifying `None` for dir_fd is always supported on all platforms.)

  To check whether a particular function accepts an open file descriptor for its dir_fd parameter, use the `in` operator on `supports_dir_fd`. As an example, this expression evaluates to `True` if `os.stat()` accepts open file descriptors for dir_fd on the local platform:

      os.stat in os.supports_dir_fd

  Currently dir_fd parameters only work on Unix platforms; none of them work on Windows.

  3.3 版新加入.

`os.``supports_effective_ids`

  A `set` object indicating whether `os.access()` permits specifying `True` for its effective_ids parameter on the local platform. (Specifying `False` for effective_ids is always supported on all platforms.) If the local platform supports it, the collection will contain `os.access()`; otherwise it will be empty.

  This expression evaluates to `True` if `os.access()` supports `effective_ids=True` on the local platform:

      os.access in os.supports_effective_ids

  Currently effective_ids is only supported on Unix platforms; it does not work on Windows.

  3.3 版新加入.

`os.``supports_fd`

  A `set` object indicating which functions in the `os` module permit specifying their path parameter as an open file descriptor on the local platform. Different platforms provide different features, and the underlying functionality Python uses to accept open file descriptors as path arguments is not available on all platforms Python supports.

  To determine whether a particular function permits specifying an open file descriptor for its path parameter, use the `in` operator on `supports_fd`. As an example, this expression evaluates to `True` if `os.chdir()` accepts open file descriptors for path on your local platform:

      os.chdir in os.supports_fd

  3.3 版新加入.

`os.``supports_follow_symlinks`

  A `set` object indicating which functions in the `os` module accept `False` for their follow_symlinks parameter on the local platform. Different platforms provide different features, and the underlying functionality Python uses to implement follow_symlinks is not available on all platforms Python supports. For consistency's sake, functions that may support follow_symlinks always allow specifying the parameter, but will throw an exception if the functionality is used when it's not locally available. (Specifying `True` for follow_symlinks is always supported on all platforms.)

  To check whether a particular function accepts `False` for its follow_symlinks parameter, use the `in` operator on `supports_follow_symlinks`. As an example, this expression evaluates to `True` if you may specify `follow_symlinks=False` when calling `os.stat()` on the local platform:

      os.stat in os.supports_follow_symlinks

  3.3 版新加入.

`os.``symlink`(src, dst, target_is_directory=False, *, dir_fd=None)

  Create a symbolic link pointing to src named dst.

  On Windows, a symlink represents either a file or a directory, and does not morph to the target dynamically. If the target is present, the type of the symlink will be created to match. Otherwise, the symlink will be created as a directory if target_is_directory is `True` or a file symlink (the default) otherwise. On non-Windows platforms, target_is_directory is ignored.

  This function can support paths relative to directory descriptors.

  備註

  On newer versions of Windows 10, unprivileged accounts can create symlinks if Developer Mode is enabled. When Developer Mode is not available/enabled, the SeCreateSymbolicLinkPrivilege privilege is required, or the process must be run as an administrator.

  `OSError` is raised when the function is called by an unprivileged user.

  可用性: Unix, Windows。

  3.2 版更變: Added support for Windows 6.0 (Vista) symbolic links.

  3.3 版新加入: Added the dir_fd argument, and now allow target_is_directory on non-Windows platforms.

  3.6 版更變: Accepts a path-like object for src and dst.

  3.8 版更變: Added support for unelevated symlinks on Windows with Developer Mode.

`os.``sync`()

  Force write of everything to disk.

  可用性: Unix。

  3.3 版新加入.

`os.``truncate`(path, length)

  Truncate the file corresponding to path, so that it is at most length bytes in size.

  This function can support specifying a file descriptor.

  Raises an auditing event `os.truncate` with arguments `path`, `length`.

  可用性: Unix, Windows。

  3.3 版新加入.

  3.5 版更變: 添加了 Windows 支持

  3.6 版更變: 接受一个 类路径对象。

`os.``unlink`(path, *, dir_fd=None)

  Remove (delete) the file path. This function is semantically identical to `remove()`; the `unlink` name is its traditional Unix name. Please see the documentation for `remove()` for further information.

  3.3 版新加入: The dir_fd parameter.

  3.6 版更變: 接受一个 类路径对象。

`os.``utime`(path, times=None, *, [ns, ]dir_fd=None, follow_symlinks=True)

  Set the access and modified times of the file specified by path.

  `utime()` takes two optional parameters, times and ns. These specify the times set on path and are used as follows:

  - If ns is specified, it must be a 2-tuple of the form `(atime_ns, mtime_ns)` where each member is an int expressing nanoseconds.

  - If times is not `None`, it must be a 2-tuple of the form `(atime, mtime)` where each member is an int or float expressing seconds.

  - If times is `None` and ns is unspecified, this is equivalent to specifying `ns=(atime_ns, mtime_ns)` where both times are the current time.

  It is an error to specify tuples for both times and ns.

  Note that the exact times you set here may not be returned by a subsequent `stat()` call, depending on the resolution with which your operating system records access and modification times; see `stat()`. The best way to preserve exact times is to use the st_atime_ns and st_mtime_ns fields from the `os.stat()` result object with the ns parameter to utime.

  This function can support specifying a file descriptor, paths relative to directory descriptors and not following symlinks.

  3.3 版新加入: Added support for specifying path as an open file descriptor, and the dir_fd, follow_symlinks, and ns parameters.

  3.6 版更變: 接受一个 类路径对象。

`os.``walk`(top, topdown=True, onerror=None, followlinks=False)

  Generate the file names in a directory tree by walking the tree either top-down or bottom-up. For each directory in the tree rooted at directory top (including top itself), it 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 contain 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 argument 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). No matter the value of topdown, the list of subdirectories is retrieved before the tuples for the directory and its subdirectories are generated.

  When topdown is `True`, the caller can modify the dirnames list in-place (perhaps using `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, impose a specific order of visiting, or even to inform `walk()` about directories the caller creates or renames before it resumes `walk()` again. Modifying dirnames when topdown is `False` has no effect on the behavior of the walk, because in bottom-up mode the directories in dirnames are generated before dirpath itself is generated.

  By default, errors from the `scandir()` call are ignored. If optional argument 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, `walk()` will not walk down into symbolic links that resolve to directories. Set followlinks to `True` to visit directories pointed to by symlinks, on systems that support them.

  備註

  Be aware that setting followlinks to `True` can lead to infinite recursion if a link points to a parent directory of itself. `walk()` does not keep track of the directories it visited already.

  備註

  If you pass a relative pathname, don't change the current working directory between resumptions of `walk()`. `walk()` never changes the current directory, and assumes that its caller doesn't either.

  This example displays the number of bytes taken by non-directory files in each directory under the starting directory, except that it doesn't look under any CVS subdirectory:

      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

  In the next example (simple implementation of `shutil.rmtree()`), walking the tree bottom-up is essential, `rmdir()` doesn't allow deleting a directory before the directory is empty:

      # Delete everything reachable from the directory named in "top",
      # assuming there are no symbolic links.
      # CAUTION:  This is dangerous!  For example, if top == '/', it
      # could delete all your disk files.
      import os
      for root, dirs, files in os.walk(top, topdown=False):
          for name in files:
              os.remove(os.path.join(root, name))
          for name in dirs:
              os.rmdir(os.path.join(root, name))

  3.5 版更變: This function now calls `os.scandir()` instead of `os.listdir()`, making it faster by reducing the number of calls to `os.stat()`.

  3.6 版更變: 接受一个 类路径对象。

`os.``fwalk`(top='.', topdown=True, onerror=None, *, follow_symlinks=False, dir_fd=None)

  This behaves exactly like `walk()`, except that it yields a 4-tuple `(dirpath, dirnames, filenames, dirfd)`, and it supports `dir_fd`.

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

  This function always supports paths relative to directory descriptors and not following symlinks. Note however that, unlike other functions, the `fwalk()` default value for follow_symlinks is `False`.

  備註

  Since `fwalk()` yields file descriptors, those are only valid until the next iteration step, so you should duplicate them (e.g. with `dup()`) if you want to keep them longer.

  This example displays the number of bytes taken by non-directory files in each directory under the starting directory, except that it doesn't look under any CVS subdirectory:

      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

  In the next example, walking the tree bottom-up is essential: `rmdir()` doesn't allow deleting a directory before the directory is empty:

      # Delete everything reachable from the directory named in "top",
      # assuming there are no symbolic links.
      # CAUTION:  This is dangerous!  For example, if top == '/', it
      # could delete all your disk files.
      import os
      for root, dirs, files, rootfd in os.fwalk(top, topdown=False):
          for name in files:
              os.unlink(name, dir_fd=rootfd)
          for name in dirs:
              os.rmdir(name, dir_fd=rootfd)

  可用性: Unix。

  3.3 版新加入.

  3.6 版更變: 接受一个 类路径对象。

  3.7 版更變: Added support for `bytes` paths.

`os.``memfd_create`(name[, flags=os.MFD_CLOEXEC])

  Create an anonymous file and return a file descriptor that refers to it. flags must be one of the `os.MFD_*` constants available on the system (or a bitwise ORed combination of them). By default, the new file descriptor is non-inheritable.

  The name supplied in name is used as a filename and will be displayed as the target of the corresponding symbolic link in the directory `/proc/self/fd/`. The displayed name is always prefixed with `memfd:` and serves only for debugging purposes. Names do not affect the behavior of the file descriptor, and as such multiple files can have the same name without any side effects.

  Availability: Linux 3.17 or newer with glibc 2.27 or newer.

  3.8 版新加入.

`os.``MFD_CLOEXEC`
`os.``MFD_ALLOW_SEALING`
`os.``MFD_HUGETLB`
`os.``MFD_HUGE_SHIFT`
`os.``MFD_HUGE_MASK`
`os.``MFD_HUGE_64KB`
`os.``MFD_HUGE_512KB`
`os.``MFD_HUGE_1MB`
`os.``MFD_HUGE_2MB`
`os.``MFD_HUGE_8MB`
`os.``MFD_HUGE_16MB`
`os.``MFD_HUGE_32MB`
`os.``MFD_HUGE_256MB`
`os.``MFD_HUGE_512MB`
`os.``MFD_HUGE_1GB`
`os.``MFD_HUGE_2GB`
`os.``MFD_HUGE_16GB`

  These flags can be passed to `memfd_create()`.

  Availability: Linux 3.17 or newer with glibc 2.27 or newer. The `MFD_HUGE*` flags are only available since Linux 4.14.

  3.8 版新加入.

### Linux 扩展属性

3.3 版新加入.

These functions are all available on Linux only.

`os.``getxattr`(path, attribute, *, follow_symlinks=True)

  Return the value of the extended filesystem attribute attribute for path. attribute can be bytes or str (directly or indirectly through the `PathLike` interface). If it is str, it is encoded with the filesystem encoding.

  This function can support specifying a file descriptor and not following symlinks.

  3.6 版更變: Accepts a path-like object for path and attribute.

`os.``listxattr`(path=None, *, follow_symlinks=True)

  Return a list of the extended filesystem attributes on path. The attributes in the list are represented as strings decoded with the filesystem encoding. If path is `None`, `listxattr()` will examine the current directory.

  This function can support specifying a file descriptor and not following symlinks.

  3.6 版更變: 接受一个 类路径对象。

`os.``removexattr`(path, attribute, *, follow_symlinks=True)

  Removes the extended filesystem attribute attribute from path. attribute should be bytes or str (directly or indirectly through the `PathLike` interface). If it is a string, it is encoded with the filesystem encoding.

  This function can support specifying a file descriptor and not following symlinks.

  3.6 版更變: Accepts a path-like object for path and attribute.

`os.``setxattr`(path, attribute, value, flags=0, *, follow_symlinks=True)

  Set the extended filesystem attribute attribute on path to value. attribute must be a bytes or str with no embedded NULs (directly or indirectly through the `PathLike` interface). If it is a str, it is encoded with the filesystem encoding. flags may be `XATTR_REPLACE` or `XATTR_CREATE`. If `XATTR_REPLACE` is given and the attribute does not exist, `EEXISTS` will be raised. If `XATTR_CREATE` is given and the attribute already exists, the attribute will not be created and `ENODATA` will be raised.

  This function can support specifying a file descriptor and not following symlinks.

  備註

  A bug in Linux kernel versions less than 2.6.39 caused the flags argument to be ignored on some filesystems.

  3.6 版更變: Accepts a path-like object for path and attribute.

`os.``XATTR_SIZE_MAX`

  The maximum size the value of an extended attribute can be. Currently, this is 64 KiB on Linux.

`os.``XATTR_CREATE`

  This is a possible value for the flags argument in `setxattr()`. It indicates the operation must create an attribute.

`os.``XATTR_REPLACE`

  This is a possible value for the flags argument in `setxattr()`. It indicates the operation must replace an existing attribute.

## Process Management

These functions may be used to create and manage processes.

The various `exec*` functions take a list of arguments for the new program loaded into the process. In each case, the first of these arguments is passed to the new program as its own name rather than as an argument a user may have typed on a command line. For the C programmer, this is the `argv[0]` passed to a program's `main()`. For example, `os.execv('/bin/echo', ['foo', 'bar'])` will only print `bar` on standard output; `foo` will seem to be ignored.

`os.``abort`()

  Generate a `SIGABRT` signal to the current process. On Unix, the default behavior is to produce a core dump; on Windows, the process immediately returns an exit code of `3`. Be aware that calling this function will not call the Python signal handler registered for `SIGABRT` with `signal.signal()`.

`os.``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.

  See the Microsoft documentation for more information about how DLLs are loaded.

  可用性: Windows。

  3.8 版新加入: Previous versions of CPython would resolve DLLs using the default behavior for the current process. This led to inconsistencies, such as only sometimes searching `PATH` or the current working directory, and OS functions such as `AddDllDirectory` having no effect.

  In 3.8, the two primary ways DLLs are loaded now explicitly override the process-wide behavior to ensure consistency. See the porting notes for information on updating libraries.

`os.``execl`(path, arg0, arg1, ...)
`os.``execle`(path, arg0, arg1, ..., env)
`os.``execlp`(file, arg0, arg1, ...)
`os.``execlpe`(file, arg0, arg1, ..., env)
`os.``execv`(path, args)
`os.``execve`(path, args, env)
`os.``execvp`(file, args)
`os.``execvpe`(file, args, env)

  These functions all execute a new program, replacing the current process; they do not return. On Unix, the new executable is loaded into the current process, and will have the same process id as the caller. Errors will be reported as `OSError` exceptions.

  The current process is replaced immediately. Open file objects and descriptors are not flushed, so if there may be data buffered on these open files, you should flush them using `sys.stdout.flush()` or `os.fsync()` before calling an `exec*` function.

  The "l" and "v" variants of the `exec*` functions differ in how command-line arguments are passed. The "l" variants are perhaps the easiest to work with if the number of parameters is fixed when the code is written; the individual parameters simply become additional parameters to the `execl*()` functions. The "v" variants are good when the number of parameters is variable, with the arguments being passed in a list or tuple as the args parameter. In either case, the arguments to the child process should start with the name of the command being run, but this is not enforced.

  The variants which include a "p" near the end (`execlp()`, `execlpe()`, `execvp()`, and `execvpe()`) will use the `PATH` environment variable to locate the program file. When the environment is being replaced (using one of the `exec*e` variants, discussed in the next paragraph), the new environment is used as the source of the `PATH` variable. The other variants, `execl()`, `execle()`, `execv()`, and `execve()`, will not use the `PATH` variable to locate the executable; path must contain an appropriate absolute or relative path.

  For `execle()`, `execlpe()`, `execve()`, and `execvpe()` (note that these all end in "e"), the env parameter must be a mapping which is used to define the environment variables for the new process (these are used instead of the current process' environment); the functions `execl()`, `execlp()`, `execv()`, and `execvp()` all cause the new process to inherit the environment of the current process.

  For `execve()` on some platforms, path may also be specified as an open file descriptor. This functionality may not be supported on your platform; you can check whether or not it is available using `os.supports_fd`. If it is unavailable, using it will raise a `NotImplementedError`.

  可用性: Unix, Windows。

  3.3 版新加入: Added support for specifying path as an open file descriptor for `execve()`.

  3.6 版更變: 接受一个 类路径对象。

`os.``_exit`(n)

  Exit the process with status n, without calling cleanup handlers, flushing stdio buffers, etc.

  備註

  The standard way to exit is `sys.exit(n)`. `_exit()` should normally only be used in the child process after a `fork()`.

The following exit codes are defined and can be used with `_exit()`, although they are not required. These are typically used for system programs written in Python, such as a mail server's external command delivery program.

備註

Some of these may not be available on all Unix platforms, since there is some variation. These constants are defined where they are defined by the underlying platform.

`os.``EX_OK`

  Exit code that means no error occurred.

  可用性: Unix。

`os.``EX_USAGE`

  Exit code that means the command was used incorrectly, such as when the wrong number of arguments are given.

  可用性: Unix。

`os.``EX_DATAERR`

  Exit code that means the input data was incorrect.

  可用性: Unix。

`os.``EX_NOINPUT`

  Exit code that means an input file did not exist or was not readable.

  可用性: Unix。

`os.``EX_NOUSER`

  Exit code that means a specified user did not exist.

  可用性: Unix。

`os.``EX_NOHOST`

  Exit code that means a specified host did not exist.

  可用性: Unix。

`os.``EX_UNAVAILABLE`

  Exit code that means that a required service is unavailable.

  可用性: Unix。

`os.``EX_SOFTWARE`

  Exit code that means an internal software error was detected.

  可用性: Unix。

`os.``EX_OSERR`

  Exit code that means an operating system error was detected, such as the inability to fork or create a pipe.

  可用性: Unix。

`os.``EX_OSFILE`

  Exit code that means some system file did not exist, could not be opened, or had some other kind of error.

  可用性: Unix。

`os.``EX_CANTCREAT`

  Exit code that means a user specified output file could not be created.

  可用性: Unix。

`os.``EX_IOERR`

  Exit code that means that an error occurred while doing I/O on some file.

  可用性: Unix。

`os.``EX_TEMPFAIL`

  Exit code that means a temporary failure occurred. This indicates something that may not really be an error, such as a network connection that couldn't be made during a retryable operation.

  可用性: Unix。

`os.``EX_PROTOCOL`

  Exit code that means that a protocol exchange was illegal, invalid, or not understood.

  可用性: Unix。

`os.``EX_NOPERM`

  Exit code that means that there were insufficient permissions to perform the operation (but not intended for file system problems).

  可用性: Unix。

`os.``EX_CONFIG`

  Exit code that means that some kind of configuration error occurred.

  可用性: Unix。

`os.``EX_NOTFOUND`

  Exit code that means something like "an entry was not found".

  可用性: Unix。

`os.``fork`()

  Fork a child process. Return `0` in the child and the child's process id in the parent. If an error occurs `OSError` is raised.

  Note that some platforms including FreeBSD <= 6.3 and Cygwin have known issues when using `fork()` from a thread.

  3.8 版更變: Calling `fork()` in a subinterpreter is no longer supported (`RuntimeError` is raised).

  警告

  See `ssl` for applications that use the SSL module with fork().

  可用性: Unix。

`os.``forkpty`()

  Fork a child process, using a new pseudo-terminal as the child's controlling terminal. Return a pair of `(pid, fd)`, where pid is `0` in the child, the new child's process id in the parent, and fd is the file descriptor of the master end of the pseudo-terminal. For a more portable approach, use the `pty` module. If an error occurs `OSError` is raised.

  3.8 版更變: Calling `forkpty()` in a subinterpreter is no longer supported (`RuntimeError` is raised).

  可用性: 某些 Unix。

`os.``kill`(pid, sig)

  Send signal sig to the process pid. Constants for the specific signals available on the host platform are defined in the `signal` module.

  Windows: The `signal.CTRL_C_EVENT` and `signal.CTRL_BREAK_EVENT` signals are special signals which can only be sent to console processes which share a common console window, e.g., some subprocesses. Any other value for sig will cause the process to be unconditionally killed by the TerminateProcess API, and the exit code will be set to sig. The Windows version of `kill()` additionally takes process handles to be killed.

  See also `signal.pthread_kill()`.

  3.2 版新加入: Windows support.

`os.``killpg`(pgid, sig)

  Send the signal sig to the process group pgid.

  可用性: Unix。

`os.``nice`(increment)

  Add increment to the process's "niceness". Return the new niceness.

  可用性: Unix。

`os.``plock`(op)

  Lock program segments into memory. The value of op (defined in `<sys/lock.h>`) determines which segments are locked.

  可用性: Unix。

`os.``popen`(cmd, mode='r', buffering=-1)

  Open a pipe to or from command cmd. The return value is an open file object connected to the pipe, which can be read or written depending on whether mode is `'r'` (default) or `'w'`. The buffering argument has the same meaning as the corresponding argument to the built-in `open()` function. The returned file object reads or writes text strings rather than bytes.

  The `close` method returns `None` if the subprocess exited successfully, or the subprocess's return code if there was an error. On POSIX systems, if the return code is positive it represents the return value of the process left-shifted by one byte. If the return code is negative, the process was terminated by the signal given by the negated value of the return code. (For example, the return value might be `- signal.SIGKILL` if the subprocess was killed.) On Windows systems, the return value contains the signed integer return code from the child process.

  This is implemented using `subprocess.Popen`; see that class's documentation for more powerful ways to manage and communicate with subprocesses.

`os.``posix_spawn`(path, argv, env, *, file_actions=None, setpgroup=None, resetids=False, setsid=False, setsigmask=(), setsigdef=(), scheduler=None)

  Wraps the `posix_spawn()` C library API for use from Python.

  Most users should use `subprocess.run()` instead of `posix_spawn()`.

  The positional-only arguments path, args, and env are similar to `execve()`.

  The path parameter is the path to the executable file.The path should contain a directory.Use `posix_spawnp()` to pass an executable file without directory.

  The file_actions argument may be a sequence of tuples describing actions to take on specific file descriptors in the child process between the C library implementation's `fork()` and `exec()` steps. The first item in each tuple must be one of the three type indicator listed below describing the remaining tuple elements:

  `os.``POSIX_SPAWN_OPEN`

    (`os.POSIX_SPAWN_OPEN`, fd, path, flags, mode)

    Performs `os.dup2(os.open(path, flags, mode), fd)`.

  `os.``POSIX_SPAWN_CLOSE`

    (`os.POSIX_SPAWN_CLOSE`, fd)

    Performs `os.close(fd)`.

  `os.``POSIX_SPAWN_DUP2`

    (`os.POSIX_SPAWN_DUP2`, fd, new_fd)

    Performs `os.dup2(fd, new_fd)`.

  These tuples correspond to the C library `posix_spawn_file_actions_addopen()`, `posix_spawn_file_actions_addclose()`, and `posix_spawn_file_actions_adddup2()` API calls used to prepare for the `posix_spawn()` call itself.

  The setpgroup argument will set the process group of the child to the value specified. If the value specified is 0, the child's process group ID will be made the same as its process ID. If the value of setpgroup is not set, the child will inherit the parent's process group ID. This argument corresponds to the C library `POSIX_SPAWN_SETPGROUP` flag.

  If the resetids argument is `True` it will reset the effective UID and GID of the child to the real UID and GID of the parent process. If the argument is `False`, then the child retains the effective UID and GID of the parent. In either case, if the set-user-ID and set-group-ID permission bits are enabled on the executable file, their effect will override the setting of the effective UID and GID. This argument corresponds to the C library `POSIX_SPAWN_RESETIDS` flag.

  If the setsid argument is `True`, it will create a new session ID for posix_spawn. setsid requires `POSIX_SPAWN_SETSID` or `POSIX_SPAWN_SETSID_NP` flag. Otherwise, `NotImplementedError` is raised.

  The setsigmask argument will set the signal mask to the signal set specified. If the parameter is not used, then the child inherits the parent's signal mask. This argument corresponds to the C library `POSIX_SPAWN_SETSIGMASK` flag.

  The sigdef argument will reset the disposition of all signals in the set specified. This argument corresponds to the C library `POSIX_SPAWN_SETSIGDEF` flag.

  The scheduler argument must be a tuple containing the (optional) scheduler policy and an instance of `sched_param` with the scheduler parameters. A value of `None` in the place of the scheduler policy indicates that is not being provided. This argument is a combination of the C library `POSIX_SPAWN_SETSCHEDPARAM` and `POSIX_SPAWN_SETSCHEDULER` flags.

  3.8 版新加入.

  可用性: Unix。

`os.``posix_spawnp`(path, argv, env, *, file_actions=None, setpgroup=None, resetids=False, setsid=False, setsigmask=(), setsigdef=(), scheduler=None)

  Wraps the `posix_spawnp()` C library API for use from Python.

  Similar to `posix_spawn()` except that the system searches for the executable file in the list of directories specified by the `PATH` environment variable (in the same way as for `execvp(3)`).

  3.8 版新加入.

  Availability: See `posix_spawn()` documentation.

`os.``register_at_fork`(*, before=None, after_in_parent=None, after_in_child=None)

  Register callables to be executed when a new child process is forked using `os.fork()` or similar process cloning APIs. The parameters are optional and keyword-only. Each specifies a different call point.

  - before is a function called before forking a child process.

  - after_in_parent is a function called from the parent process after forking a child process.

  - after_in_child is a function called from the child process.

  These calls are only made if control is expected to return to the Python interpreter. A typical `subprocess` launch will not trigger them as the child is not going to re-enter the interpreter.

  Functions registered for execution before forking are called in reverse registration order. Functions registered for execution after forking (either in the parent or in the child) are called in registration order.

  Note that `fork()` calls made by third-party C code may not call those functions, unless it explicitly calls `PyOS_BeforeFork()`, `PyOS_AfterFork_Parent()` and `PyOS_AfterFork_Child()`.

  There is no way to unregister a function.

  可用性: Unix。

  3.7 版新加入.

`os.``spawnl`(mode, path, ...)
`os.``spawnle`(mode, path, ..., env)
`os.``spawnlp`(mode, file, ...)
`os.``spawnlpe`(mode, file, ..., env)
`os.``spawnv`(mode, path, args)
`os.``spawnve`(mode, path, args, env)
`os.``spawnvp`(mode, file, args)
`os.``spawnvpe`(mode, file, args, env)

  Execute the program path in a new process.

  (Note that the `subprocess` module provides more powerful facilities for spawning new processes and retrieving their results; using that module is preferable to using these functions. Check especially the Replacing Older Functions with the subprocess Module section.)

  If mode is `P_NOWAIT`, this function returns the process id of the new process; if mode is `P_WAIT`, returns the process's exit code if it exits normally, or `-signal`, where signal is the signal that killed the process. On Windows, the process id will actually be the process handle, so can be used with the `waitpid()` function.

  Note on VxWorks, this function doesn't return `-signal` when the new process is killed. Instead it raises OSError exception.

  The "l" and "v" variants of the `spawn*` functions differ in how command-line arguments are passed. The "l" variants are perhaps the easiest to work with if the number of parameters is fixed when the code is written; the individual parameters simply become additional parameters to the `spawnl*()` functions. The "v" variants are good when the number of parameters is variable, with the arguments being passed in a list or tuple as the args parameter. In either case, the arguments to the child process must start with the name of the command being run.

  The variants which include a second "p" near the end (`spawnlp()`, `spawnlpe()`, `spawnvp()`, and `spawnvpe()`) will use the `PATH` environment variable to locate the program file. When the environment is being replaced (using one of the `spawn*e` variants, discussed in the next paragraph), the new environment is used as the source of the `PATH` variable. The other variants, `spawnl()`, `spawnle()`, `spawnv()`, and `spawnve()`, will not use the `PATH` variable to locate the executable; path must contain an appropriate absolute or relative path.

  For `spawnle()`, `spawnlpe()`, `spawnve()`, and `spawnvpe()` (note that these all end in "e"), the env parameter must be a mapping which is used to define the environment variables for the new process (they are used instead of the current process' environment); the functions `spawnl()`, `spawnlp()`, `spawnv()`, and `spawnvp()` all cause the new process to inherit the environment of the current process. Note that keys and values in the env dictionary must be strings; invalid keys or values will cause the function to fail, with a return value of `127`.

  As an example, the following calls to `spawnlp()` and `spawnvpe()` are equivalent:

      import os
      os.spawnlp(os.P_WAIT, 'cp', 'cp', 'index.html', '/dev/null')

      L = ['cp', 'index.html', '/dev/null']
      os.spawnvpe(os.P_WAIT, 'cp', L, os.environ)

  Availability: Unix, Windows. `spawnlp()`, `spawnlpe()`, `spawnvp()` and `spawnvpe()` are not available on Windows. `spawnle()` and `spawnve()` are not thread-safe on Windows; we advise you to use the `subprocess` module instead.

  3.6 版更變: 接受一个 类路径对象。

`os.``P_NOWAIT`
`os.``P_NOWAITO`

  Possible values for the mode parameter to the `spawn*` family of functions. If either of these values is given, the `spawn*()` functions will return as soon as the new process has been created, with the process id as the return value.

  可用性: Unix, Windows。

`os.``P_WAIT`

  Possible value for the mode parameter to the `spawn*` family of functions. If this is given as mode, the `spawn*()` functions will not return until the new process has run to completion and will return the exit code of the process the run is successful, or `-signal` if a signal kills the process.

  可用性: Unix, Windows。

`os.``P_DETACH`
`os.``P_OVERLAY`

  Possible values for the mode parameter to the `spawn*` family of functions. These are less portable than those listed above. `P_DETACH` is similar to `P_NOWAIT`, but the new process is detached from the console of the calling process. If `P_OVERLAY` is used, the current process will be replaced; the `spawn*` function will not return.

  可用性: Windows。

`os.``startfile`(path[, operation])

  Start a file with its associated application.

  When operation is not specified or `'open'`, this acts like double-clicking the file in Windows Explorer, or giving the file name as an argument to the start command from the interactive command shell: the file is opened with whatever application (if any) its extension is associated.

  When another operation is given, it must be a "command verb" that specifies what should be done with the file. Common verbs documented by Microsoft are `'print'` and `'edit'` (to be used on files) as well as `'explore'` and `'find'` (to be used on directories).

  `startfile()` returns as soon as the associated application is launched. There is no option to wait for the application to close, and no way to retrieve the application's exit status. The path parameter is relative to the current directory. If you want to use an absolute path, make sure the first character is not a slash (`'/'`); the underlying Win32 `ShellExecute()` function doesn't work if it is. Use the `os.path.normpath()` function to ensure that the path is properly encoded for Win32.

  To reduce interpreter startup overhead, the Win32 `ShellExecute()` function is not resolved until this function is first called. If the function cannot be resolved, `NotImplementedError` will be raised.

  可用性: Windows。

`os.``system`(command)

  Execute the command (a string) in a subshell. This is implemented by calling the Standard C function `system()`, and has the same limitations. Changes to `sys.stdin`, etc. are not reflected in the environment of the executed command. If command generates any output, it will be sent to the interpreter standard output stream.

  On Unix, the return value is the exit status of the process encoded in the format specified for `wait()`. Note that POSIX does not specify the meaning of the return value of the C `system()` function, so the return value of the Python function is system-dependent.

  On Windows, the return value is that returned by the system shell after running command. The shell is given by the Windows environment variable `COMSPEC`: it is usually cmd.exe, which returns the exit status of the command run; on systems using a non-native shell, consult your shell documentation.

  The `subprocess` module provides more powerful facilities for spawning new processes and retrieving their results; using that module is preferable to using this function. See the Replacing Older Functions with the subprocess Module section in the `subprocess` documentation for some helpful recipes.

  Raises an auditing event `os.system` with argument `command`.

  可用性: Unix, Windows。

`os.``times`()

  Returns the current global process times. The return value is an object with five attributes:

  - `user` - user time

  - `system` - system time

  - `children_user` - user time of all child processes

  - `children_system` - system time of all child processes

  - `elapsed` - elapsed real time since a fixed point in the past

  For backwards compatibility, this object also behaves like a five-tuple containing `user`, `system`, `children_user`, `children_system`, and `elapsed` in that order.

  See the Unix manual page times(2) and times(3) manual page on Unix or the GetProcessTimes MSDN <https://docs.microsoft.com/windows/win32/api/processthreadsapi/nf-processthreadsapi-getprocesstimes> _ on Windows. On Windows, only `user` and `system` are known; the other attributes are zero.

  可用性: Unix, Windows。

  3.3 版更變: 返回结果的类型由元组变成一个类似元组的对象，同时具有命名的属性。

`os.``wait`()

  Wait for completion of a child process, and return a tuple containing its pid and exit status indication: a 16-bit number, whose low byte is the signal number that killed the process, and whose high byte is the exit status (if the signal number is zero); the high bit of the low byte is set if a core file was produced.

  可用性: Unix。

`os.``waitid`(idtype, id, options)

  Wait for the completion of one or more child processes. idtype can be `P_PID`, `P_PGID` or `P_ALL`. id specifies the pid to wait on. options is constructed from the ORing of one or more of `WEXITED`, `WSTOPPED` or `WCONTINUED` and additionally may be ORed with `WNOHANG` or `WNOWAIT`. The return value is an object representing the data contained in the `siginfo_t` structure, namely: `si_pid`, `si_uid`, `si_signo`, `si_status`, `si_code` or `None` if `WNOHANG` is specified and there are no children in a waitable state.

  可用性: Unix。

  3.3 版新加入.

`os.``P_PID`
`os.``P_PGID`
`os.``P_ALL`

  These are the possible values for idtype in `waitid()`. They affect how id is interpreted.

  可用性: Unix。

  3.3 版新加入.

`os.``WEXITED`
`os.``WSTOPPED`
`os.``WNOWAIT`

  Flags that can be used in options in `waitid()` that specify what child signal to wait for.

  可用性: Unix。

  3.3 版新加入.

`os.``CLD_EXITED`
`os.``CLD_DUMPED`
`os.``CLD_TRAPPED`
`os.``CLD_CONTINUED`

  These are the possible values for `si_code` in the result returned by `waitid()`.

  可用性: Unix。

  3.3 版新加入.

`os.``waitpid`(pid, options)

  The details of this function differ on Unix and Windows.

  On Unix: Wait for completion of a child process given by process id pid, and return a tuple containing its process id and exit status indication (encoded as for `wait()`). The semantics of the call are affected by the value of the integer options, which should be `0` for normal operation.

  If pid is greater than `0`, `waitpid()` requests status information for that specific process. If pid is `0`, the request is for the status of any child in the process group of the current process. If pid is `-1`, the request pertains to any child of the current process. If pid is less than `-1`, status is requested for any process in the process group `-pid` (the absolute value of pid).

  An `OSError` is raised with the value of errno when the syscall returns -1.

  On Windows: Wait for completion of a process given by process handle pid, and return a tuple containing pid, and its exit status shifted left by 8 bits (shifting makes cross-platform use of the function easier). A pid less than or equal to `0` has no special meaning on Windows, and raises an exception. The value of integer options has no effect. pid can refer to any process whose id is known, not necessarily a child process. The `spawn*` functions called with `P_NOWAIT` return suitable process handles.

  3.5 版更變: 如果系统调用被中断，但信号处理程序没有触发异常，此函数现在会重试系统调用，而不是触发 `InterruptedError` 异常 (原因详见 PEP 475)。

`os.``wait3`(options)

  Similar to `waitpid()`, except no process id argument is given and a 3-element tuple containing the child's process id, exit status indication, and resource usage information is returned. Refer to `resource`.`getrusage()` for details on resource usage information. The option argument is the same as that provided to `waitpid()` and `wait4()`.

  可用性: Unix。

`os.``wait4`(pid, options)

  Similar to `waitpid()`, except a 3-element tuple, containing the child's process id, exit status indication, and resource usage information is returned. Refer to `resource`.`getrusage()` for details on resource usage information. The arguments to `wait4()` are the same as those provided to `waitpid()`.

  可用性: Unix。

`os.``WNOHANG`

  The option for `waitpid()` to return immediately if no child process status is available immediately. The function returns `(0, 0)` in this case.

  可用性: Unix。

`os.``WCONTINUED`

  This option causes child processes to be reported if they have been continued from a job control stop since their status was last reported.

  可用性: 部分 Unix 系统。

`os.``WUNTRACED`

  This option causes child processes to be reported if they have been stopped but their current state has not been reported since they were stopped.

  可用性: Unix。

The following functions take a process status code as returned by `system()`, `wait()`, or `waitpid()` as a parameter. They may be used to determine the disposition of a process.

`os.``WCOREDUMP`(status)

  Return `True` if a core dump was generated for the process, otherwise return `False`.

  可用性: Unix。

`os.``WIFCONTINUED`(status)

  Return `True` if the process has been continued from a job control stop, otherwise return `False`.

  可用性: Unix。

`os.``WIFSTOPPED`(status)

  Return `True` if the process has been stopped, otherwise return `False`.

  可用性: Unix。

`os.``WIFSIGNALED`(status)

  Return `True` if the process exited due to a signal, otherwise return `False`.

  可用性: Unix。

`os.``WIFEXITED`(status)

  Return `True` if the process exited using the exit(2) system call, otherwise return `False`.

  可用性: Unix。

`os.``WEXITSTATUS`(status)

  如果 `WIFEXITED(status)` 为值，则将整数形参返回给 exit(2) 系统调用。 否则，返回值将没有任何意义。

  可用性: Unix。

`os.``WSTOPSIG`(status)

  返回导致进程停止的信号。

  可用性: Unix。

`os.``WTERMSIG`(status)

  返回导致进程退出的信号。

  可用性: Unix。

## 调度器接口

这些函数控制操作系统如何为进程分配 CPU 时间。 它们仅在某些 Unix 平台上可用。 更多细节信息请查阅你所用 Unix 的指南页面。

3.3 版新加入.

以下调度策略如果被操作系统支持就会对外公开。

`os.``SCHED_OTHER`

  默认调度策略。

`os.``SCHED_BATCH`

  用于 CPU 密集型进程的调度策略，它会尽量为计算机中的其余任务保留交互性。

`os.``SCHED_IDLE`

  用于极低优先级的后台任务的调度策略。

`os.``SCHED_SPORADIC`

  用于偶发型服务程序的调度策略。

`os.``SCHED_FIFO`

  先进先出的调度策略。

`os.``SCHED_RR`

  循环式的调度策略。

`os.``SCHED_RESET_ON_FORK`

  此旗标可与任何其他调度策略进行 OR 运算。 当带有此旗标的进程设置分叉时，其子进程的调度策略和优先级会被重置为默认值。

class `os.``sched_param`(sched_priority)

  这个类表示在 `sched_setparam()`, `sched_setscheduler()` 和 `sched_getparam()` 中使用的可修改调度形参。 它属于不可变对象。

  目前它只有一个可能的形参：

  `sched_priority`

    一个调度策略的调度优先级。

`os.``sched_get_priority_min`(policy)

  获取 policy 的最小优先级数值。 policy 是以上调度策略常量之一。

`os.``sched_get_priority_max`(policy)

  获取 policy 的最高优先级数值。 policy 是以上调度策略常量之一。

`os.``sched_setscheduler`(pid, policy, param)

  Set the scheduling policy for the process with PID pid. A pid of 0 means the calling process. policy is one of the scheduling policy constants above. param is a `sched_param` instance.

`os.``sched_getscheduler`(pid)

  Return the scheduling policy for the process with PID pid. A pid of 0 means the calling process. The result is one of the scheduling policy constants above.

`os.``sched_setparam`(pid, param)

  Set a scheduling parameters for the process with PID pid. A pid of 0 means the calling process. param is a `sched_param` instance.

`os.``sched_getparam`(pid)

  Return the scheduling parameters as a `sched_param` instance for the process with PID pid. A pid of 0 means the calling process.

`os.``sched_rr_get_interval`(pid)

  Return the round-robin quantum in seconds for the process with PID pid. A pid of 0 means the calling process.

`os.``sched_yield`()

  Voluntarily relinquish the CPU.

`os.``sched_setaffinity`(pid, mask)

  Restrict the process with PID pid (or the current process if zero) to a set of CPUs. mask is an iterable of integers representing the set of CPUs to which the process should be restricted.

`os.``sched_getaffinity`(pid)

  Return the set of CPUs the process with PID pid (or the current process if zero) is restricted to.

## Miscellaneous System Information

`os.``confstr`(name)

  Return string-valued system configuration values. name specifies the configuration value to retrieve; it may be a string which is the name of a defined system value; these names are specified in a number of standards (POSIX, Unix 95, Unix 98, and others). Some platforms define additional names as well. The names known to the host operating system are given as the keys of the `confstr_names` dictionary. For configuration variables not included in that mapping, passing an integer for name is also accepted.

  If the configuration value specified by name isn't defined, `None` is returned.

  If name is a string and is not known, `ValueError` is raised. If a specific value for name is not supported by the host system, even if it is included in `confstr_names`, an `OSError` is raised with `errno.EINVAL` for the error number.

  可用性: Unix。

`os.``confstr_names`

  Dictionary mapping names accepted by `confstr()` to the integer values defined for those names by the host operating system. This can be used to determine the set of names known to the system.

  可用性: Unix。

`os.``cpu_count`()

  Return the number of CPUs in the system. Returns `None` if undetermined.

  该数量不同于当前进程可以使用的CPU数量。可用的CPU数量可以由 `len(os.sched_getaffinity(0))` 方法获得。

  3.4 版新加入.

`os.``getloadavg`()

  Return the number of processes in the system run queue averaged over the last 1, 5, and 15 minutes or raises `OSError` if the load average was unobtainable.

  可用性: Unix。

`os.``sysconf`(name)

  Return integer-valued system configuration values. If the configuration value specified by name isn't defined, `-1` is returned. The comments regarding the name parameter for `confstr()` apply here as well; the dictionary that provides information on the known names is given by `sysconf_names`.

  可用性: Unix。

`os.``sysconf_names`

  Dictionary mapping names accepted by `sysconf()` to the integer values defined for those names by the host operating system. This can be used to determine the set of names known to the system.

  可用性: Unix。

The following data values are used to support path manipulation operations. These are defined for all platforms.

Higher-level operations on pathnames are defined in the `os.path` module.

`os.``curdir`

  The constant string used by the operating system to refer to the current directory. This is `'.'` for Windows and POSIX. Also available via `os.path`.

`os.``pardir`

  The constant string used by the operating system to refer to the parent directory. This is `'..'` for Windows and POSIX. Also available via `os.path`.

`os.``sep`

  The character used by the operating system to separate pathname components. This is `'/'` for POSIX and `'\\'` for Windows. Note that knowing this is not sufficient to be able to parse or concatenate pathnames --- use `os.path.split()` and `os.path.join()` --- but it is occasionally useful. Also available via `os.path`.

`os.``altsep`

  An alternative character used by the operating system to separate pathname components, or `None` if only one separator character exists. This is set to `'/'` on Windows systems where `sep` is a backslash. Also available via `os.path`.

`os.``extsep`

  The character which separates the base filename from the extension; for example, the `'.'` in `os.py`. Also available via `os.path`.

`os.``pathsep`

  The character conventionally used by the operating system to separate search path components (as in `PATH`), such as `':'` for POSIX or `';'` for Windows. Also available via `os.path`.

`os.``defpath`

  The default search path used by `exec*p*` and `spawn*p*` if the environment doesn't have a `'PATH'` key. Also available via `os.path`.

`os.``linesep`

  The string used to separate (or, rather, terminate) lines on the current platform. This may be a single character, such as `'\n'` for POSIX, or multiple characters, for example, `'\r\n'` for Windows. Do not use os.linesep as a line terminator when writing files opened in text mode (the default); use a single `'\n'` instead, on all platforms.

`os.``devnull`

  The file path of the null device. For example: `'/dev/null'` for POSIX, `'nul'` for Windows. Also available via `os.path`.

`os.``RTLD_LAZY`
`os.``RTLD_NOW`
`os.``RTLD_GLOBAL`
`os.``RTLD_LOCAL`
`os.``RTLD_NODELETE`
`os.``RTLD_NOLOAD`
`os.``RTLD_DEEPBIND`

  Flags for use with the `setdlopenflags()` and `getdlopenflags()` functions. See the Unix manual page dlopen(3) for what the different flags mean.

  3.3 版新加入.

## Random numbers

`os.``getrandom`(size, flags=0)

  Get up to size random bytes. The function can return less bytes than requested.

  These bytes can be used to seed user-space random number generators or for cryptographic purposes.

  `getrandom()` relies on entropy gathered from device drivers and other sources of environmental noise. Unnecessarily reading large quantities of data will have a negative impact on other users of the `/dev/random` and `/dev/urandom` devices.

  The flags argument is a bit mask that can contain zero or more of the following values ORed together: `os.GRND_RANDOM` and `GRND_NONBLOCK`.

  See also the Linux getrandom() manual page.

  Availability: Linux 3.17 and newer.

  3.6 版新加入.

`os.``urandom`(size)

  Return a string of size random bytes suitable for cryptographic use.

  This function returns random bytes from an OS-specific randomness source. The returned data should be unpredictable enough for cryptographic applications, though its exact quality depends on the OS implementation.

  On Linux, if the `getrandom()` syscall is available, it is used in blocking mode: block until the system urandom entropy pool is initialized (128 bits of entropy are collected by the kernel). See the PEP 524 for the rationale. On Linux, the `getrandom()` function can be used to get random bytes in non-blocking mode (using the `GRND_NONBLOCK` flag) or to poll until the system urandom entropy pool is initialized.

  On a Unix-like system, random bytes are read from the `/dev/urandom` device. If the `/dev/urandom` device is not available or not readable, the `NotImplementedError` exception is raised.

  On Windows, it will use `CryptGenRandom()`.

  也參考

  The `secrets` module provides higher level functions. For an easy-to-use interface to the random number generator provided by your platform, please see `random.SystemRandom`.

  3.6.0 版更變: On Linux, `getrandom()` is now used in blocking mode to increase the security.

  3.5.2 版更變: On Linux, if the `getrandom()` syscall blocks (the urandom entropy pool is not initialized yet), fall back on reading `/dev/urandom`.

  3.5 版更變: On Linux 3.17 and newer, the `getrandom()` syscall is now used when available. On OpenBSD 5.6 and newer, the C `getentropy()` function is now used. These functions avoid the usage of an internal file descriptor.

`os.``GRND_NONBLOCK`

  By default, when reading from `/dev/random`, `getrandom()` blocks if no random bytes are available, and when reading from `/dev/urandom`, it blocks if the entropy pool has not yet been initialized.

  If the `GRND_NONBLOCK` flag is set, then `getrandom()` does not block in these cases, but instead immediately raises `BlockingIOError`.

  3.6 版新加入.

`os.``GRND_RANDOM`

  If this bit is set, then random bytes are drawn from the `/dev/random` pool instead of the `/dev/urandom` pool.

  3.6 版新加入.