# 16.1. `os` — 操作系统接口模块

源代码： Lib/os.py

该模块提供了一些方便使用操作系统相关功能的函数。 如果你是想读写一个文件，请参阅 `open()`，如果你想操作路径，请参阅 `os.path` 模块，如果你想在命令行上读取所有文件中的所有行请参阅 `fileinput` 模块。 有关创建临时文件和目录的方法，请参阅 `tempfile` 模块，对于高级文件目录处理，请参阅 `shutil` 模块。

关于这些函数的适用性的说明：

- 所有 Python 内建的操作系统相关的模块的设计都是为了使得在同一功能可用的情况下，保持接口的一致性；例如，函数 `os.stat(path)` 以相同的格式返回关于 path 的统计信息（这个函数同时也是起源于 POSIX 接口）。

- 针对特定的操作的拓展同样在可用于 `os` 模块，但是使用它们必然会对可移植性产生威胁。

- 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。

- An 「Availability: Unix」 note means that this function is commonly found on Unix systems. It does not make any claims about its existence on a specific operating system.

- If not separately noted, all functions that claim 「Availability: Unix」 are supported on Mac OS X, which builds on a Unix core.

備註

All functions in this module raise `OSError` in the case of invalid or inaccessible file names and paths, or other arguments that have the correct type, but are not accepted by the operating system.

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。

## 16.1.1. 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 。

## 16.1.2. 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。

  Availability: 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）。

  `environb` is only available if `supports_bytes_environ` is True.

  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()`。

  Availability: most flavors of Unix, 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()` is only available if `supports_bytes_environ` is True.

  Availability: most flavors of Unix.

  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。

  Availability: Unix.

`os.``geteuid`()

  返回当前进程的有效用户ID。

  Availability: Unix.

`os.``getgid`()

  返回当前进程的实际组ID。

  Availability: 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。

  Availability: Unix.

  3.3 版新加入.

`os.``getgroups`()

  返回当前进程关联的附加组ID列表

  Availability: 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。

  Availability: 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

  Availability: Unix.

`os.``getpgrp`()

  返回当时进程组的ID

  Availability: 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。

  Availability: 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。

  Availability: Unix.

  3.3 版新加入.

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

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

  Availability: 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和暂存用户ID。

  Availability: 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。

  Availability: Unix.

  3.2 版新加入.

`os.``getuid`()

  返回当前进程的真实用户ID。

  Availability: 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。

  Availability: 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。

  Availability: most flavors of Unix, 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。

  Availability: Unix.

`os.``seteuid`(euid)

  设置当前进程的有效用户ID。

  Availability: Unix.

`os.``setgid`(gid)

  设置当前进程的组ID。

  Availability: 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。

  Availability: 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。

  Availability: 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。

  Availability: 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。

  Availability: 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。

  Availability: Unix.

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

  设置当前进程的真实，有效和暂存组ID。

  Availability: 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。

  Availability: 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。

  Availability: Unix.

`os.``getsid`(pid)

  调用系统调用 `getsid()`。 相关语义请参阅 Unix 手册。

  Availability: Unix.

`os.``setsid`()

  使用系统调用 `getsid()`。相关说明，请参考 Unix 手册。

  Availability: Unix.

`os.``setuid`(uid)

  设置当前进程的用户ID。

  Availability: 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())`。

  Availability: recent flavors of Unix.

  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。

  Availability: most flavors of Unix, Windows.

## 16.1.3. 创建文件对象

该函数创建新的 文件对象。 （另见 `open()` 关于打开文件的说明。）

`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。

## 16.1.4. 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。关闭由内建函数 `open()` ， `popen()` 或 `fdopen()` 返回的 「文件对象」，则使用其相应的 `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.``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)

  Duplicate file descriptor fd to fd2, closing the latter first if necessary. The file descriptor fd2 is inheritable by default, or non-inheritable if inheritable is `False`.

  3.4 版更變: 添加可选参数 inheritable。

`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)`。

  Availability: 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)`。

  Availability: 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。

  Availability: 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)`。

  Availability: 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)`。

  Availability: 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。

  Availability: Unix, Windows.

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

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

  Availability: 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()`。

  Availability: 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。

  Availability: 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。

  Availability: 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。

  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 path-like object。

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。

  Availability: some flavors of 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。

  Availability: 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)`。

  Availability: some flavors of 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。

  Availability: 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`。

  Availability: 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。

  Availability: Unix.

  3.3 版新加入.

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

  Read from a file descriptor, fd, at a position of offset. It will read up to buffersize number of bytes. The file offset remains unchanged.

  Availability: Unix.

  3.3 版新加入.

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

  Write bytestring to a file descriptor, fd, from offset, leaving the file offset unchanged.

  Availability: Unix.

  3.3 版新加入.

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

  Read at most n bytes from file descriptor fd. Return a bytestring containing the bytes read. If the end of the file referred to by fd has been reached, an empty bytes object is returned.

  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。读取由内建函数 `open()`、`popen()`、`fdopen()` 或 `sys.stdin` 返回的 「文件对象」，则使用其相应的 `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。

  Availability: 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()`。

  Availability: 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）。

  Availability: Unix.

  3.3 版新加入.

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

  Read from a file descriptor fd into a number of mutable bytes-like objects buffers. `readv()` will transfer data into each buffer until it is full and then move on to the next buffer in the sequence to hold the rest of the data. `readv()` returns the total number of bytes read (which may be less than the total capacity of all the objects).

  Availability: Unix.

  3.3 版新加入.

`os.``tcgetpgrp`(fd)

  返回与 fd 给定的终端相关联的进程组（fd 是由 `os.open()` 返回的已打开文件的描述符）。

  Availability: 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）。

  Availability: 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。

  Availability: Unix.

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

  Write the bytestring in str to file descriptor fd. Return the number of bytes actually written.

  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)

  Write the contents of buffers to file descriptor fd. buffers must be a sequence of bytes-like objects. Buffers are processed in array order. Entire contents of first buffer is written before proceeding to second, and so on. The operating system may set a limit (sysconf() value SC_IOV_MAX) on the number of buffers that can be used.

  `writev()` writes the contents of each object to the file descriptor and returns the total number of bytes written.

  Availability: Unix.

  3.3 版新加入.

### 16.1.4.1. 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``（列，行）``，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。

  Availability: 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。

### 16.1.4.2. 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，子进程中不可继承的文件描述符会被关闭，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）。

  Availability: Windows.

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

  设置指定句柄的“可继承”标志位。

  Availability: Windows.

## 16.1.5. 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：

- specifying a file descriptor: For some functions, the path argument can be not only a string giving a path name, but also a file descriptor. The function will then operate on the file referred to by the descriptor. (For POSIX systems, Python will call the `f...` version of the function.)

  You can check whether or not path can be specified as a file descriptor on your platform using `os.supports_fd`. If it is unavailable, using it will raise a `NotImplementedError`.

  If the function also supports dir_fd or follow_symlinks arguments, it is an error to specify one of those when supplying path as a file descriptor.

- paths relative to directory descriptors: If dir_fd is not `None`, it should be a file descriptor referring to a directory, and the path to operate on should be relative; path will then be relative to that directory. If the path is absolute, dir_fd is ignored. (For POSIX systems, Python will call the `...at` or `f...at` version of the function.)

  You can check whether or not dir_fd is supported on your platform using `os.supports_dir_fd`. If it is unavailable, using it will raise a `NotImplementedError`.

- not following symlinks: If follow_symlinks is `False`, and the last element of the path to operate on is a symbolic link, the function will operate on the symbolic link itself instead of the file the link points to. (For POSIX systems, Python will call the `l...` version of the function.)

  You can check whether or not follow_symlinks is supported on your platform using `os.supports_follow_symlinks`. If it is unavailable, using it will raise a `NotImplementedError`.

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

  使用真实的 uid/gid 测试对 path 的访问。请注意，大多数测试操作将使用有效的 uid/gid，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

  使用 `access()` 来检查用户是否具有某项权限（如打开文件的权限），然后再使用 `open()` 打开文件，这样做存在一个安全漏洞，因为用户可能会在检查和打开文件之间的时间里做其他操作。推荐使用 EAFP 技术。如:

      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

  即使 `access()` 指示 I/O 操作会成功，但实际操作仍可能失败，尤其是对网络文件系统的操作，其权限语义可能超出常规的 POSIX 权限位模型。

  3.3 版更變: 添加 dir_fd、effective_ids 和 follow_symlinks 参数。

  3.6 版更變: 接受一个 path-like object。

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

  作为 `access()` 的 mode 参数的可选值，分别测试 path 的存在性、可读性、可写性和可执行性。

`os.``chdir`(path)

  将当前工作目录更改为 path。

  本函数支持 指定文件描述符为参数。其中，描述符必须指向打开的目录，不能是打开的文件。

  3.3 版新加入: 在某些平台上新增支持将 path 参数指定为文件描述符。

  3.6 版更變: 接受一个 path-like object。

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

  将 path 标志设置为数字 标志。标志 可以用以下值按位或组合起来（以下值在 `stat` 模块中定义）：

  - `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.

  Availability: Unix.

  3.3 版新加入: The follow_symlinks argument.

  3.6 版更變: 接受一个 path-like object。

`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 path-like object。

`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.

  Availability: Unix.

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

  Availability: Unix.

  3.6 版更變: 接受一个 path-like object。

`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)`.

  Availability: Unix.

`os.``getcwd`()

  Return a string representing the current working directory.

`os.``getcwdb`()

  Return a bytestring representing the current working directory.

`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)`.

  Availability: Unix.

  3.6 版更變: 接受一个 path-like object。

`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)`.

  Availability: Unix.

  3.6 版更變: 接受一个 path-like object。

`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)`.

  Availability: Unix.

  3.6 版更變: 接受一个 path-like object。

`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.

  Availability: 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.

  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 an open file descriptor for path.

  3.6 版更變: 接受一个 path-like object。

`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.

`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 path-like object。

`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()`; see the mkdir() description for how it is interpreted.

  If exist_ok is `False` (the default), an `OSError` 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 path-like object。

`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.

  Availability: Unix.

  3.3 版新加入: dir_fd 参数。

  3.6 版更變: 接受一个 path-like object。

`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.

  Availability: Unix.

  3.3 版新加入: dir_fd 参数。

  3.6 版更變: 接受一个 path-like object。

`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.

  Availability: Unix.

  3.6 版更變: 接受一个 path-like object。

`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.

  Availability: 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.

  Availability: 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: 接受一个 path-like object。

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

  Remove (delete) the file path. If path is a directory, `OSError` 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 path-like object。

`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 path-like object。

`os.``rename`(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. On Unix, if dst exists and is a file, 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). On Windows, if dst already exists, `OSError` will be raised even if it is a file.

  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. Only works when the directory is empty, otherwise, `OSError` is raised. 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 path-like object。

`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`.

  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.

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.

    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 symbolic link.

    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.

  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 path-like object。

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.

  See also the `stat_float_times()` function.

  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 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 attribute is 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.

  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.

`os.``stat_float_times`([newvalue])

  Determine whether `stat_result` represents time stamps as float objects. If newvalue is `True`, future calls to `stat()` return floats, if it is `False`, future calls return ints. If newvalue is omitted, return the current setting.

  For compatibility with older Python versions, accessing `stat_result` as a tuple always returns integers.

  Python now returns float values by default. Applications which do not work correctly with floating point time stamps can use this function to restore the old behaviour.

  The resolution of the timestamps (that is the smallest possible fraction) depends on the system. Some systems only support second resolution; on these systems, the fraction will always be zero.

  It is recommended that this setting is only changed at program startup time in the __main__ module; libraries should never change this setting. If an application uses a library that works incorrectly if floating point time stamps are processed, this application should turn the feature off until the library has been corrected.

  3.3 版後已棄用.

`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`.

  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.

  Availability: 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 an open file descriptor for path.

  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 path-like object。

`os.``supports_dir_fd`

  A `Set` object indicating which functions in the `os` module permit use of their dir_fd parameter. Different platforms provide different functionality, and an option that might work on one might be unsupported on another. For consistency’s sakes, functions that support dir_fd always allow specifying the parameter, but will raise an exception if the functionality is not actually available.

  To check whether a particular function permits use of its dir_fd parameter, use the `in` operator on `supports_dir_fd`. As an example, this expression determines whether the dir_fd parameter of `os.stat()` is locally available:

      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 which functions in the `os` module permit use of the effective_ids parameter for `os.access()`. If the local platform supports it, the collection will contain `os.access()`, otherwise it will be empty.

  To check whether you can use the effective_ids parameter for `os.access()`, use the `in` operator on `supports_effective_ids`, like so:

      os.access in os.supports_effective_ids

  Currently effective_ids only works 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. Different platforms provide different functionality, and an option that might work on one might be unsupported on another. For consistency’s sakes, functions that support fd always allow specifying the parameter, but will raise an exception if the functionality is not actually available.

  To check 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 determines whether `os.chdir()` accepts open file descriptors when called 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 permit use of their follow_symlinks parameter. Different platforms provide different functionality, and an option that might work on one might be unsupported on another. For consistency’s sakes, functions that support follow_symlinks always allow specifying the parameter, but will raise an exception if the functionality is not actually available.

  To check whether a particular function permits use of its follow_symlinks parameter, use the `in` operator on `supports_follow_symlinks`. As an example, this expression determines whether the follow_symlinks parameter of `os.stat()` is locally available:

      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.

  Symbolic link support was introduced in Windows 6.0 (Vista). `symlink()` will raise a `NotImplementedError` on Windows versions earlier than 6.0.

  This function can support paths relative to directory descriptors.

  備註

  On Windows, the SeCreateSymbolicLinkPrivilege is required in order to successfully create symlinks. This privilege is not typically granted to regular users but is available to accounts which can escalate privileges to the administrator level. Either obtaining the privilege or running your application as an administrator are ways to successfully create symlinks.

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

  Availability: 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.

`os.``sync`()

  Force write of everything to disk.

  Availability: 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.

  Availability: 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 path-like object。

`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 path-like object。

`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.

  Whether a directory can be given for path depends on whether the operating system implements directories as files (for example, Windows does not). 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 an open file descriptor for path, and the dir_fd, follow_symlinks, and ns parameters.

  3.6 版更變: 接受一个 path-like object。

`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 path-like object。

`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)

  Availability: Unix.

  3.3 版新加入.

  3.6 版更變: 接受一个 path-like object。

### 16.1.5.1. 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 path-like object。

`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.

## 16.1.6. 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.``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`.

  Availability: Unix, Windows.

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

  3.6 版更變: 接受一个 path-like object。

`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.

  Availability: Unix.

`os.``EX_USAGE`

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

  Availability: Unix.

`os.``EX_DATAERR`

  Exit code that means the input data was incorrect.

  Availability: Unix.

`os.``EX_NOINPUT`

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

  Availability: Unix.

`os.``EX_NOUSER`

  Exit code that means a specified user did not exist.

  Availability: Unix.

`os.``EX_NOHOST`

  Exit code that means a specified host did not exist.

  Availability: Unix.

`os.``EX_UNAVAILABLE`

  Exit code that means that a required service is unavailable.

  Availability: Unix.

`os.``EX_SOFTWARE`

  Exit code that means an internal software error was detected.

  Availability: Unix.

`os.``EX_OSERR`

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

  Availability: 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.

  Availability: Unix.

`os.``EX_CANTCREAT`

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

  Availability: Unix.

`os.``EX_IOERR`

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

  Availability: 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.

  Availability: Unix.

`os.``EX_PROTOCOL`

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

  Availability: Unix.

`os.``EX_NOPERM`

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

  Availability: Unix.

`os.``EX_CONFIG`

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

  Availability: Unix.

`os.``EX_NOTFOUND`

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

  Availability: 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.

  警告

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

  Availability: 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.

  Availability: some flavors of 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.

  Availability: Unix.

`os.``nice`(increment)

  Add increment to the process’s 「niceness」. Return the new niceness.

  Availability: Unix.

`os.``plock`(op)

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

  Availability: 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.``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.

  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 path-like object。

`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.

  Availability: 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.

  Availability: 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.

  Availability: 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.

  Availability: 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.

  Availability: 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) or the corresponding Windows Platform API documentation. On Windows, only `user` and `system` are known; the other attributes are zero.

  Availability: 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.

  Availability: 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.

  Availability: 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.

  Availability: 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.

  Availability: 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()`.

  Availability: 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()`.

  Availability: 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()`.

  Availability: 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.

  Availability: 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.

  Availability: some Unix systems.

`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.

  Availability: 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`.

  Availability: Unix.

`os.``WIFCONTINUED`(status)

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

  Availability: Unix.

`os.``WIFSTOPPED`(status)

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

  Availability: Unix.

`os.``WIFSIGNALED`(status)

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

  Availability: Unix.

`os.``WIFEXITED`(status)

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

  Availability: 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。

  Availability: Unix.

`os.``WSTOPSIG`(status)

  返回导致进程停止的信号。

  Availability: Unix.

`os.``WTERMSIG`(status)

  返回导致进程退出的信号。

  Availability: Unix.

## 16.1.7. 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 的最低优先级数值。 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.

## 16.1.8. 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.

  Availability: 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.

  Availability: 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.

  Availability: 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`.

  Availability: 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.

  Availability: 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.

## 16.1.9. 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.