os — 操作系統接口模塊 · Python3.7.3官方文檔簡體中文

### 導航 - [索引](../genindex.xhtml "總目錄") - [模塊](../py-modindex.xhtml "Python 模塊索引") | - [下一頁](io.xhtml "io --- 處理流的核心工具") | - [上一頁](allos.xhtml "通用操作系統服務") | - ![](https://box.kancloud.cn/a721fc7ec672275e257bbbfde49a4d4e_16x16.png) - [Python](https://www.python.org/) ? - zh\_CN 3.7.3 [文檔](../index.xhtml) ? - [Python 標準庫](index.xhtml) ? - [通用操作系統服務](allos.xhtml) ? - $('.inline-search').show(0); | # [`os`](#module-os "os: Miscellaneous operating system interfaces.") --- 操作系統接口模塊 **源代碼：** [Lib/os.py](https://github.com/python/cpython/tree/3.7/Lib/os.py) \[https://github.com/python/cpython/tree/3.7/Lib/os.py\] - - - - - - 該模塊提供了一些方便使用操作系統相關功能的函數。如果你是想讀寫一個文件，請參閱 [`open()`](functions.xhtml#open "open")，如果你想操作路徑，請參閱 [`os.path`](os.path.xhtml#module-os.path "os.path: Operations on pathnames.") 模塊，如果你想在命令行上讀取所有文件中的所有行請參閱 [`fileinput`](fileinput.xhtml#module-fileinput "fileinput: Loop over standard input or a list of files.") 模塊。有關創建臨時文件和目錄的方法，請參閱 [`tempfile`](tempfile.xhtml#module-tempfile "tempfile: Generate temporary files and directories.") 模塊，對于高級文件目錄處理，請參閱 [`shutil`](shutil.xhtml#module-shutil "shutil: High-level file operations, including copying.") 模塊。關于這些函數的可用性的說明： - 所有 Python 內建的操作系統相關的模塊的設計都是為了使得在同一功能可用的情況下，保持接口的一致性；例如，函數 `os.stat(path)` 以相同的格式返回關于 *path* 的統計信息（這個函數同時也是起源于 POSIX 接口）。 - 針對特定的操作的拓展同樣在可用于 [`os`](#module-os "os: Miscellaneous operating system interfaces.") 模塊，但是使用它們必然會對可移植性產生威脅。 - 所有接受路徑或文件名的函數都同時支持字節串和字符串對象，并在返回路徑或文件名時使用相應類型的對象作為結果。注解此模塊的所有函數在遇到不可用或不可訪問的文件名或路徑，以及其他類型正確，但不被操作系統接受的參數時，會引發 [`OSError`](exceptions.xhtml#OSError "OSError") 異常。 *exception* `os.``error`內建的 [`OSError`](exceptions.xhtml#OSError "OSError") 異常的一個別名。 `os.``name`導入的依賴特定操作系統的模塊的名稱。以下名稱目前已注冊: `'posix'`, `'nt'`, `'java'`. 參見 [`sys.platform`](sys.xhtml#sys.platform "sys.platform") 有更詳細的描述. [`os.uname()`](#os.uname "os.uname") 只給出系統提供的版本信息。 [`platform`](platform.xhtml#module-platform "platform: Retrieves as much platform identifying data as possible.") 模塊對系統的標識有更詳細的檢查。 ## 文件名，命令行參數，以及環境變量。在 Python 中，使用字符串類型表示文件名、命令行參數和環境變量。在某些系統上，在將這些字符串傳遞給操作系統之前，必須將這些字符串解碼為字節。 Python 使用文件系統編碼來執行此轉換（請參閱 [`sys.getfilesystemencoding()`](sys.xhtml#sys.getfilesystemencoding "sys.getfilesystemencoding") ）。在 3.1 版更改: 在某些系統上，使用文件系統編碼進行轉換可能會失敗。在這種情況下，Python 會使用 [代理轉義編碼錯誤處理器](codecs.xhtml#surrogateescape)，這意味著在解碼時，不可解碼的字節被 Unicode 字符 U+DCxx 替換，并且這些字節在編碼時再次轉換為原始字節。文件系統編碼必須保證成功解碼小于 128 的所有字節。如果文件系統編碼無法提供此保證， API 函數可能會引發 UnicodeErrors 。 ## 進程參數這些函數和數據項提供了操作當前進程和用戶的信息。 `os.``ctermid`()返回與進程控制終端對應的文件名。 [可用性](intro.xhtml#availability): Unix。 `os.``environ`一個表示字符串環境的 [mapping](../glossary.xhtml#term-mapping) 對象。例如，`environ['HOME']` 是你的主目錄（在某些平臺上）的路徑名，相當于 C 中的 `getenv("HOME")`。這個映射是在第一次導入 [`os`](#module-os "os: Miscellaneous operating system interfaces.") 模塊時捕獲的，通常作為 Python 啟動時處理 `site.py` 的一部分。除了通過直接修改 `os.environ` 之外，在此之后對環境所做的更改不會反映在 `os.environ` 中。如果平臺支持 [`putenv()`](#os.putenv "os.putenv") 函數，這個映射除了可以用于查詢環境外還能用于修改環境。當這個映射被修改時，[`putenv()`](#os.putenv "os.putenv") 將被自動調用。在Unix系統上，鍵和值會使用 [`sys.getfilesystemencoding()`](sys.xhtml#sys.getfilesystemencoding "sys.getfilesystemencoding") 和 `'surrogateescape'` 的錯誤處理。如果你想使用其他的編碼，使用 [`environb`](#os.environb "os.environb")。注解直接調用 [`putenv()`](#os.putenv "os.putenv") 并不會影響 `os.environ`，所以推薦直接修改``os.environ``。注解在某些平臺上，包括 FreeBSD 和 Mac OS X，設置 `environ` 可能導致內存泄露。參閱 `putenv()` 的系統文檔。如果平臺沒有提供 [`putenv()`](#os.putenv "os.putenv"), 為了使啟動的子進程使用修改后的環境，一份修改后的映射會被傳給合適的進程創建函數。如果平臺支持 [`unsetenv()`](#os.unsetenv "os.unsetenv") 函數，你可以通過刪除映射中元素的方式來刪除對應的環境變量。當一個元素被從 `os.environ` 刪除時，以及 `pop()` 或 `clear()` 被調用時， [`unsetenv()`](#os.unsetenv "os.unsetenv") 會被自動調用。 `os.``environb`字節版本的 [`environ`](#os.environ "os.environ"): 一個以字節串表示環境的 [mapping](../glossary.xhtml#term-mapping) 對象。 [`environ`](#os.environ "os.environ") 和 [`environb`](#os.environb "os.environb") 是同步的（修改 [`environb`](#os.environb "os.environb") 會更新 [`environ`](#os.environ "os.environ")，反之亦然）。只有在 [`supports_bytes_environ`](#os.supports_bytes_environ "os.supports_bytes_environ") 為 True 的時候 [`environb`](#os.environb "os.environb") 才是可用的。 3\.2 新版功能. `os.``chdir`(*path*)`os.``fchdir`(*fd*)`os.``getcwd`()以上函數請參閱 [Files and Directories](#os-file-dir) 。 `os.``fsencode`(*filename*)編碼 [路徑類](../glossary.xhtml#term-path-like-object) *文件名* 為文件系統接受的形式，使用 `'surrogateescape'` 代理轉義編碼錯誤處理器，在Windows系統上會使用 `'strict'` ；返回 [`bytes`](stdtypes.xhtml#bytes "bytes") 字節類型不變。 [`fsdecode()`](#os.fsdecode "os.fsdecode") 是此函數的逆向函數。 3\.2 新版功能. 在 3.6 版更改: 增加對實現了 [`os.PathLike`](#os.PathLike "os.PathLike") 接口的對象的支持。 `os.``fsdecode`(*filename*)從文件系統編碼方式解碼為 [路徑類](../glossary.xhtml#term-path-like-object) 文件名，使用 `'surrogateescape'` 代理轉義編碼錯誤處理器，在Windows系統上會使用 `'strict'` ；返回 [`str`](stdtypes.xhtml#str "str") 字符串不變。 [`fsencode()`](#os.fsencode "os.fsencode") 是此函數的逆向函數。 3\.2 新版功能. 在 3.6 版更改: 增加對實現了 [`os.PathLike`](#os.PathLike "os.PathLike") 接口的對象的支持。 `os.``fspath`(*path*)返回路徑的文件系統表示。如果傳入的是 [`str`](stdtypes.xhtml#str "str") 或 [`bytes`](stdtypes.xhtml#bytes "bytes") 類型的字符串，將原樣返回。否則 [`__fspath__()`](#os.PathLike.__fspath__ "os.PathLike.__fspath__") 將被調用，如果得到的是一個 [`str`](stdtypes.xhtml#str "str") 或 [`bytes`](stdtypes.xhtml#bytes "bytes") 類型的對象，那就返回這個值。其他所有情況則會拋出 [`TypeError`](exceptions.xhtml#TypeError "TypeError") 異常。 3\.6 新版功能. *class* `os.``PathLike`描述表示一個文件系統路徑的 [abstract base class](../glossary.xhtml#term-abstract-base-class) ，如 [`pathlib.PurePath`](pathlib.xhtml#pathlib.PurePath "pathlib.PurePath") 。 3\.6 新版功能. *abstractmethod* `__fspath__`()返回當前對象的文件系統表示。這個方法只應該返回一個 [`str`](stdtypes.xhtml#str "str") 字符串或 [`bytes`](stdtypes.xhtml#bytes "bytes") 字節串，請優先選擇 [`str`](stdtypes.xhtml#str "str") 字符串。 `os.``getenv`(*key*, *default=None*)如果存在，返回環境變量 *key* 的值，否則返回 *default*。 *key* ， *default* 和返回值均為 str 字符串類型。在Unix系統上，鍵和值會使用 [`sys.getfilesystemencoding()`](sys.xhtml#sys.getfilesystemencoding "sys.getfilesystemencoding") 和``'surrogateescape'`` 錯誤處理進行解碼。如果你想使用其他的編碼，使用 [`os.getenvb()`](#os.getenvb "os.getenvb")。 [可用性](intro.xhtml#availability): 大部分的Unix系統，Windows。 `os.``getenvb`(*key*, *default=None*)如果存在環境變量 *key* 那么返回其值，否則返回 *default*。 *key* ， *default* 和返回值均為bytes字節串類型。 [`getenvb()`](#os.getenvb "os.getenvb") 僅在 [`supports_bytes_environ`](#os.supports_bytes_environ "os.supports_bytes_environ") 為 True 時可用 [可用性](intro.xhtml#availability): 大部分的Unix系統。 3\.2 新版功能. `os.``get_exec_path`(*env=None*)返回將用于搜索可執行文件的目錄列表，與在外殼程序中啟動一個進程時相似。指定的 *env* 應為用于搜索 PATH 的環境變量字典。默認情況下，當 *env* 為 `None` 時，將會使用 [`environ`](#os.environ "os.environ") 。 3\.2 新版功能. `os.``getegid`()返回當前進程的有效組ID。對應當前進程執行文件的 "set id" 位。 [可用性](intro.xhtml#availability): Unix。 `os.``geteuid`()返回當前進程的有效用戶ID。 [可用性](intro.xhtml#availability): Unix。 `os.``getgid`()返回當前進程的實際組ID。 [可用性](intro.xhtml#availability): Unix。 `os.``getgrouplist`(*user*, *group*)返回該用戶所在的組 ID 列表。可能 *group* 參數沒有在返回的列表中，實際上用戶應該也是屬于該 *group*。*group* 參數一般可以從儲存賬戶信息的密碼記錄文件中找到。 [可用性](intro.xhtml#availability): Unix。 3\.3 新版功能. `os.``getgroups`()返回當前進程對應的組ID列表 [可用性](intro.xhtml#availability): Unix。注解在Mac OS X系統中，[`getgroups()`](#os.getgroups "os.getgroups") 會和其他 Unix 平臺有些不同。如果 Python 解釋器是在 `10.5` 或更早版本中部署，[`getgroups()`](#os.getgroups "os.getgroups") 返回當前用戶進程相關的有效組ID列表。該列表長度由于系統預設的接口限制，最長為 16。而且在適當的權限下，返回結果還會因 [`getgroups()`](#os.getgroups "os.getgroups") 而發生變化；如果 Python 解釋器是在 `10.5` 以上版本中部署，[`getgroups()`](#os.getgroups "os.getgroups") 返回進程所屬有效用戶 ID 所對應的用戶的組 ID 列表，組用戶列表可能因為進程的生存周期而發生變動，而且也不會因為 [`setgroups()`](#os.setgroups "os.setgroups") 的調用而發生，返回的組用戶列表長度也沒有長度 16 的限制。在部署中，Python 解釋器用到的變量 `MACOSX_DEPLOYMENT_TARGET` 可以用 [`sysconfig.get_config_var()`](sysconfig.xhtml#sysconfig.get_config_var "sysconfig.get_config_var")。 `os.``getlogin`()返回通過控制終端進程進行登錄的用戶名。在多數情況下，使用 [`getpass.getuser()`](getpass.xhtml#getpass.getuser "getpass.getuser") 會更有效，因為后者會通過檢查環境變量 `LOGNAME` 或 `USERNAME` 來查找用戶，再由 `pwd.getpwuid(os.getuid())[0]` 來獲取當前用戶 ID 的登錄名。 [可用性](intro.xhtml#availability): Unix, Windows。 `os.``getpgid`(*pid*)根據進程id *pid* 返回進程的組 ID 列表。如果 *pid* 為 0，則返回當前進程的進程組 ID 列表 [可用性](intro.xhtml#availability): Unix。 `os.``getpgrp`()返回當時進程組的ID [可用性](intro.xhtml#availability): Unix。 `os.``getpid`()返回當前進程ID `os.``getppid`()返回父進程ID。當父進程已經結束，在Unix中返回的ID是初始進程(1)中的一個，在Windows中仍然是同一個進程ID，該進程ID有可能已經被進行進程所占用。 [可用性](intro.xhtml#availability): Unix, Windows。在 3.2 版更改: 添加WIndows的支持。 `os.``getpriority`(*which*, *who*)獲取程序調度優先級。*which* 參數值可以是 [`PRIO_PROCESS`](#os.PRIO_PROCESS "os.PRIO_PROCESS")，[`PRIO_PGRP`](#os.PRIO_PGRP "os.PRIO_PGRP")，或 [`PRIO_USER`](#os.PRIO_USER "os.PRIO_USER") 中的一個，*who* 是相對于 *which* ([`PRIO_PROCESS`](#os.PRIO_PROCESS "os.PRIO_PROCESS") 的進程標識符，[`PRIO_PGRP`](#os.PRIO_PGRP "os.PRIO_PGRP") 的進程組標識符和 [`PRIO_USER`](#os.PRIO_USER "os.PRIO_USER") 的用戶ID)。當 *who* 為 0 時（分別）表示調用的進程，調用進程的進程組或調用進程所屬的真實用戶 ID。 [可用性](intro.xhtml#availability): Unix。 3\.3 新版功能. `os.``PRIO_PROCESS``os.``PRIO_PGRP``os.``PRIO_USER`函數 [`getpriority()`](#os.getpriority "os.getpriority") 和 [`setpriority()`](#os.setpriority "os.setpriority") 的參數。 [可用性](intro.xhtml#availability): Unix。 3\.3 新版功能. `os.``getresuid`()返回一個由 (ruid, euid, suid) 所組成的元組，分別表示當前進程的真實用戶ID，有效用戶ID和甲暫存用戶ID。 [可用性](intro.xhtml#availability): Unix。 3\.2 新版功能. `os.``getresgid`()返回一個由 (rgid, egid, sgid) 所組成的元組，分別表示當前進程的真實組ID，有效組ID和暫存組ID。 [可用性](intro.xhtml#availability): Unix。 3\.2 新版功能. `os.``getuid`()返回當前進程的真實用戶ID。 [可用性](intro.xhtml#availability): Unix。 `os.``initgroups`(*username*, *gid*)調用系統 initgroups()，使用指定用戶所在的所有值來初始化組訪問列表，包括指定的組ID。 [可用性](intro.xhtml#availability): Unix。 3\.2 新版功能. `os.``putenv`(*key*, *value*)將名為 *key* 的環境變量值設置為 *value*。該變量名修改會影響由 [`os.system()`](#os.system "os.system")， [`popen()`](#os.popen "os.popen") ，[`fork()`](#os.fork "os.fork") 和 [`execv()`](#os.execv "os.execv") 發起的子進程。 [可用性](intro.xhtml#availability): 大部分的Unix系統，Windows。注解在一些平臺，包括 FreeBSD 和 Mac OS X，設置 `environ` 可能導致內存泄露。詳情參考 putenv 相關系統文檔。當系統支持 [`putenv()`](#os.putenv "os.putenv") 時，`os.environ` 中的參數賦值會自動轉換為對 [`putenv()`](#os.putenv "os.putenv") 的調用。不過 [`putenv()`](#os.putenv "os.putenv") 的調用不會更新 `os.environ`，因此最好使用 `os.environ` 對變量賦值。 `os.``setegid`(*egid*)設置當前進程的有效組ID。 [可用性](intro.xhtml#availability): Unix。 `os.``seteuid`(*euid*)設置當前進程的有效用戶ID。 [可用性](intro.xhtml#availability): Unix。 `os.``setgid`(*gid*)設置當前進程的組ID。 [可用性](intro.xhtml#availability): Unix。 `os.``setgroups`(*groups*)將 *group* 參數值設置為與當進程相關聯的附加組ID列表。*group* 參數必須為一個序列，每個元素應為每個組的數字ID。該操作通常只適用于超級用戶。 [可用性](intro.xhtml#availability): Unix。注解在 Mac OS X 中，*groups* 的長度不能超過系統定義的最大有效組 ID 個數，一般為 16。如果它沒有返回與調用 setgroups() 所設置的相同的組列表，請參閱 [`getgroups()`](#os.getgroups "os.getgroups") 的文檔。 `os.``setpgrp`()根據已實現的版本（如果有）來調用系統 `setpgrp()` 或 `setpgrp(0, 0)` 。相關說明，請參考 Unix 手冊。 [可用性](intro.xhtml#availability): Unix。 `os.``setpgid`(*pid*, *pgrp*)使用系統調用 `setpgid()`，將 *pid* 對應進程的組ID設置為 *pgrp*。相關說明，請參考 Unix 手冊。 [可用性](intro.xhtml#availability): Unix。 `os.``setpriority`(*which*, *who*, *priority*)設置程序調度優先級。 *which* 的值為 [`PRIO_PROCESS`](#os.PRIO_PROCESS "os.PRIO_PROCESS"), [`PRIO_PGRP`](#os.PRIO_PGRP "os.PRIO_PGRP") 或 [`PRIO_USER`](#os.PRIO_USER "os.PRIO_USER") 之一，而 *who* 會相對于 *which* ([`PRIO_PROCESS`](#os.PRIO_PROCESS "os.PRIO_PROCESS") 的進程標識符, [`PRIO_PGRP`](#os.PRIO_PGRP "os.PRIO_PGRP") 的進程組標識符和 [`PRIO_USER`](#os.PRIO_USER "os.PRIO_USER") 的用戶 ID) 被解析。 *who* 值為零 (分別) 表示調用進程，調用進程的進程組或調用進程的真實用戶 ID。 *priority* 是范圍在 -20 至 19 的值。默認優先級為 0；較小的優先級數值會更優先被調度。 [可用性](intro.xhtml#availability): Unix。 3\.3 新版功能. `os.``setregid`(*rgid*, *egid*)設置當前進程的真實和有效組ID。 [可用性](intro.xhtml#availability): Unix。 `os.``setresgid`(*rgid*, *egid*, *sgid*)設置當前進程的真實，有效和暫存組ID。 [可用性](intro.xhtml#availability): Unix。 3\.2 新版功能. `os.``setresuid`(*ruid*, *euid*, *suid*)設置當前進程的真實，有效和暫存用戶ID。 [可用性](intro.xhtml#availability): Unix。 3\.2 新版功能. `os.``setreuid`(*ruid*, *euid*)設置當前進程的真實和有效用戶ID。 [可用性](intro.xhtml#availability): Unix。 `os.``getsid`(*pid*)調用系統調用 `getsid()`。相關語義請參閱 Unix 手冊。 [可用性](intro.xhtml#availability): Unix。 `os.``setsid`()使用系統調用 `getsid()`。相關說明，請參考 Unix 手冊。 [可用性](intro.xhtml#availability): Unix。 `os.``setuid`(*uid*)設置當前進程的用戶ID。 [可用性](intro.xhtml#availability): Unix。 `os.``strerror`(*code*)根據 *code* 中的錯誤碼返回錯誤消息。在某些平臺上當給出未知錯誤碼時 `strerror()` 將返回 `NULL` 并會引發 [`ValueError`](exceptions.xhtml#ValueError "ValueError")。 `os.``supports_bytes_environ`如果操作系統上原生環境類型是字節型則為 `True` (例如在 Windows 上為 `False`)。 3\.2 新版功能. `os.``umask`(*mask*)設定當前數值掩碼并返回之前的掩碼。 `os.``uname`()返回當前操作系統的識別信息。返回值是一個有5個屬性的對象： - `sysname` - 操作系統名 - `nodename` - 機器在網絡上的名稱（需要先設定） - `release` - 操作系統發行信息 - `version` - 操作系統版本信息 - `machine` - 硬件標識符為了向后兼容，該對象也是可迭代的，像是一個按照 `sysname`，`nodename`，`release`，`version`，和 `machine` 順序組成的元組。有些系統會將 `nodename` 截短為 8 個字符或截短至前綴部分；獲取主機名的一個更好方式是 [`socket.gethostname()`](socket.xhtml#socket.gethostname "socket.gethostname") 或甚至可以用 `socket.gethostbyaddr(socket.gethostname())`。 [可用性](intro.xhtml#availability): 較新的 Unix 版本。在 3.3 版更改: 返回結果的類型由元組變成一個類似元組的對象，同時具有命名的屬性。 `os.``unsetenv`(*key*)取消設置（刪除）名為 *key* 的環境變量。變量名的改變會影響由 [`os.system()`](#os.system "os.system")，[`popen()`](#os.popen "os.popen")，[`fork()`](#os.fork "os.fork") 和 [`execv()`](#os.execv "os.execv") 觸發的子進程。當系統支持 [`unsetenv()`](#os.unsetenv "os.unsetenv") ，刪除在 `os.environ` 中的變量會自動轉換為對 [`unsetenv()`](#os.unsetenv "os.unsetenv") 的調用。但是 [`unsetenv()`](#os.unsetenv "os.unsetenv") 不能更新 `os.environ`，因此最好直接刪除 `os.environ` 中的變量。 [可用性](intro.xhtml#availability): 大部分的Unix系統，Windows。 ## 創建文件對象該函數創建新的 [文件對象](../glossary.xhtml#term-file-object)。（另見 [`open()`](#os.open "os.open") 關于打開文件的說明。） `os.``fdopen`(*fd*, *\*args*, *\*\*kwargs*)返回打開文件描述符 *fd* 對應文件的對象。類似內建 [`open()`](functions.xhtml#open "open") 函數，二者接受同樣的參數。不同之處在于 [`fdopen()`](#os.fdopen "os.fdopen") 第一個參數應該為整數。 ## 文件描述符操作這些函數對文件描述符所引用的 I/O 流進行操作。文件描述符是一些小的整數，對應于當前進程所打開的文件。例如，標準輸入的文件描述符通常是0，標準輸出是1，標準錯誤是2。之后被進程打開的文件的文件描述符會被依次指定為3，4，5等。“文件描述符”這個詞有點誤導性，在 Unix 平臺中套接字和管道也被文件描述符所引用。當需要時，可以用 [`fileno()`](io.xhtml#io.IOBase.fileno "io.IOBase.fileno") 可以獲得 [file object](../glossary.xhtml#term-file-object) 所對應的文件描述符。需要注意的是，直接使用文件描述符會繞過文件對象的方法，會忽略如數據內部緩沖等情況。 `os.``close`(*fd*)關閉文件描述符 *fd*。注解該功能適用于低級 I/O 操作，必須用于 [`os.open()`](#os.open "os.open") 或 [`pipe()`](#os.pipe "os.pipe") 返回的文件描述符。關閉由內建函數 [`open()`](functions.xhtml#open "open") ， [`popen()`](#os.popen "os.popen") 或 [`fdopen()`](#os.fdopen "os.fdopen") 返回的 "文件對象"，則使用其相應的 [`close()`](io.xhtml#io.IOBase.close "io.IOBase.close") 方法。 `os.``closerange`(*fd\_low*, *fd\_high*)關閉從 *fd\_low* （包括）到 *fd\_high* （排除）間的文件描述符，并忽略錯誤。類似（但快于）: ``` for fd in range(fd_low, fd_high): try: os.close(fd) except OSError: pass ``` `os.``device_encoding`(*fd*)如果連接到終端，則返回一個與 *fd* 關聯的設備描述字符，否則返回 [`None`](constants.xhtml#None "None")。 `os.``dup`(*fd*)返回一個文件描述符 *fd* 的副本。該文件描述符的副本是 [不可繼承的](#fd-inheritance)。在 Windows 中，當復制一個標準流（0: stdin, 1: stdout, 2: stderr）時，新的文件描述符是 [可繼承的](#fd-inheritance)。在 3.4 版更改: 新的文件描述符現在是不可繼承的。 `os.``dup2`(*fd*, *fd2*, *inheritable=True*)把文件描述符 *fd* 復制為 *fd2*，必要時先關閉后者。返回 *fd2*。新的文件描述符默認是 [可繼承的](#fd-inheritance)，除非在 *inheritable* 為 `False` 時，是不可繼承的。在 3.4 版更改: 添加可選參數 *inheritable*。在 3.7 版更改: 成功時返回 *fd2*，以過去的版本中，總是返回 `None`。 `os.``fchmod`(*fd*, *mode*)將 *fd* 指定文件的權限狀態修改為 *mode*。可以參考 [`chmod()`](#os.chmod "os.chmod") 中列出 *mode* 的可用值。從Python 3.3開始，這相當于 `os.chmod(fd, mode)`。 [可用性](intro.xhtml#availability): Unix。 `os.``fchown`(*fd*, *uid*, *gid*)分別將 *fd* 指定文件的所有者和組 ID 修改為 *uid* 和 *gid* 的值。若不想變更其中的某個 ID，可將相應值設為 -1。參考 [`chown()`](#os.chown "os.chown")。從 Python 3.3 開始，這相當于 `os.chown(fd, uid, gid)`。 [可用性](intro.xhtml#availability): Unix。 `os.``fdatasync`(*fd*)強制將文件描述符 *fd* 指定文件寫入磁盤。不強制更新元數據。 [可用性](intro.xhtml#availability): Unix。注解該功能在 MacOS 中不可用。 `os.``fpathconf`(*fd*, *name*)Return system configuration information relevant to an open 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. If *name* is a string and is not known, [`ValueError`](exceptions.xhtml#ValueError "ValueError") is raised. If a specific value for *name* is not supported by the host system, even if it is included in `pathconf_names`, an [`OSError`](exceptions.xhtml#OSError "OSError") is raised with [`errno.EINVAL`](errno.xhtml#errno.EINVAL "errno.EINVAL") for the error number. 從 Python 3.3 起，此功能等價于 `os.pathconf(fd, name)`。 [可用性](intro.xhtml#availability): Unix。 `os.``fstat`(*fd*)獲取文件描述符 *fd* 的狀態. 返回一個 [`stat_result`](#os.stat_result "os.stat_result") 對象。從 Python 3.3 起，此功能等價于 `os.stat(fd)`。參見 [`stat()`](#os.stat "os.stat") 函數。 `os.``fstatvfs`(*fd*)Return information about the filesystem containing the file associated with file descriptor *fd*, like [`statvfs()`](#os.statvfs "os.statvfs"). As of Python 3.3, this is equivalent to `os.statvfs(fd)`. [可用性](intro.xhtml#availability): Unix。 `os.``fsync`(*fd*)Force write of file with filedescriptor *fd* to disk. On Unix, this calls the native `fsync()` function; on Windows, the MS `_commit()` function. If you're starting with a buffered Python [file object](../glossary.xhtml#term-file-object) *f*, first do `f.flush()`, and then do `os.fsync(f.fileno())`, to ensure that all internal buffers associated with *f* are written to disk. [可用性](intro.xhtml#availability): Unix, Windows。 `os.``ftruncate`(*fd*, *length*)Truncate the file corresponding to file descriptor *fd*, so that it is at most *length* bytes in size. As of Python 3.3, this is equivalent to `os.truncate(fd, length)`. [可用性](intro.xhtml#availability): Unix, Windows。在 3.5 版更改: 添加了 Windows 支持 `os.``get_blocking`(*fd*)Get the blocking mode of the file descriptor: `False` if the [`O_NONBLOCK`](#os.O_NONBLOCK "os.O_NONBLOCK") flag is set, `True` if the flag is cleared. See also [`set_blocking()`](#os.set_blocking "os.set_blocking") and [`socket.socket.setblocking()`](socket.xhtml#socket.socket.setblocking "socket.socket.setblocking"). [可用性](intro.xhtml#availability): Unix。 3\.5 新版功能. `os.``isatty`(*fd*)Return `True` if the file descriptor *fd* is open and connected to a tty(-like) device, else `False`. `os.``lockf`(*fd*, *cmd*, *len*)Apply, test or remove a POSIX lock on an open file descriptor. *fd* is an open file descriptor. *cmd* specifies the command to use - one of [`F_LOCK`](#os.F_LOCK "os.F_LOCK"), [`F_TLOCK`](#os.F_TLOCK "os.F_TLOCK"), [`F_ULOCK`](#os.F_ULOCK "os.F_ULOCK") or [`F_TEST`](#os.F_TEST "os.F_TEST"). *len* specifies the section of the file to lock. [可用性](intro.xhtml#availability): Unix。 3\.3 新版功能. `os.``F_LOCK``os.``F_TLOCK``os.``F_ULOCK``os.``F_TEST`Flags that specify what action [`lockf()`](#os.lockf "os.lockf") will take. [可用性](intro.xhtml#availability): Unix。 3\.3 新版功能. `os.``lseek`(*fd*, *pos*, *how*)Set the current position of file descriptor *fd* to position *pos*, modified by *how*: [`SEEK_SET`](#os.SEEK_SET "os.SEEK_SET") or `0` to set the position relative to the beginning of the file; [`SEEK_CUR`](#os.SEEK_CUR "os.SEEK_CUR") or `1` to set it relative to the current position; [`SEEK_END`](#os.SEEK_END "os.SEEK_END") or `2` to set it relative to the end of the file. Return the new cursor position in bytes, starting from the beginning. `os.``SEEK_SET``os.``SEEK_CUR``os.``SEEK_END`Parameters to the [`lseek()`](#os.lseek "os.lseek") function. Their values are 0, 1, and 2, respectively. 3\.3 新版功能: Some operating systems could support additional values, like `os.SEEK_HOLE` or `os.SEEK_DATA`. `os.``open`(*path*, *flags*, *mode=0o777*, *\**, *dir\_fd=None*)Open the file *path* and set various flags according to *flags* and possibly its mode according to *mode*. When computing *mode*, the current umask value is first masked out. Return the file descriptor for the newly opened file. The new file descriptor is [non-inheritable](#fd-inheritance). For a description of the flag and mode values, see the C run-time documentation; flag constants (like [`O_RDONLY`](#os.O_RDONLY "os.O_RDONLY") and [`O_WRONLY`](#os.O_WRONLY "os.O_WRONLY")) are defined in the [`os`](#module-os "os: Miscellaneous operating system interfaces.") module. In particular, on Windows adding [`O_BINARY`](#os.O_BINARY "os.O_BINARY") is needed to open files in binary mode. This function can support [paths relative to directory descriptors](#dir-fd) with the *dir\_fd* parameter. 在 3.4 版更改: 新的文件描述符現在是不可繼承的。注解 This function is intended for low-level I/O. For normal usage, use the built-in function [`open()`](functions.xhtml#open "open"), which returns a [file object](../glossary.xhtml#term-file-object) with `read()` and `write()` methods (and many more). To wrap a file descriptor in a file object, use [`fdopen()`](#os.fdopen "os.fdopen"). 3\.3 新版功能: *dir\_fd* 參數。在 3.5 版更改: 如果系統調用被中斷，但信號處理程序沒有觸發異常，此函數現在會重試系統調用，而不是觸發 [`InterruptedError`](exceptions.xhtml#InterruptedError "InterruptedError") 異常 (原因詳見 [**PEP 475**](https://www.python.org/dev/peps/pep-0475) \[https://www.python.org/dev/peps/pep-0475\])。在 3.6 版更改: 接受一個 [類路徑對象](../glossary.xhtml#term-path-like-object)。 The following constants are options for the *flags* parameter to the [`open()`](#os.open "os.open") function. They can be combined using the bitwise OR operator `|`. Some of them are not available on all platforms. For descriptions of their availability and use, consult the *open(2)* manual page on Unix or [the MSDN](https://msdn.microsoft.com/en-us/library/z0kc8e3z.aspx) \[https://msdn.microsoft.com/en-us/library/z0kc8e3z.aspx\] on Windows. `os.``O_RDONLY``os.``O_WRONLY``os.``O_RDWR``os.``O_APPEND``os.``O_CREAT``os.``O_EXCL``os.``O_TRUNC`The above constants are available on Unix and Windows. `os.``O_DSYNC``os.``O_RSYNC``os.``O_SYNC``os.``O_NDELAY``os.``O_NONBLOCK``os.``O_NOCTTY``os.``O_CLOEXEC`這個常數僅在 Unix 系統中可用。在 3.3 版更改: Add [`O_CLOEXEC`](#os.O_CLOEXEC "os.O_CLOEXEC") constant. `os.``O_BINARY``os.``O_NOINHERIT``os.``O_SHORT_LIVED``os.``O_TEMPORARY``os.``O_RANDOM``os.``O_SEQUENTIAL``os.``O_TEXT`這個常數僅在 Windows 系統中可用。 `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`The above constants are extensions and not present if they are not defined by the C library. 在 3.4 版更改: Add [`O_PATH`](#os.O_PATH "os.O_PATH") on systems that support it. Add [`O_TMPFILE`](#os.O_TMPFILE "os.O_TMPFILE"), only available on Linux Kernel 3.11 or newer. `os.``openpty`()Open a new pseudo-terminal pair. Return a pair of file descriptors `(master, slave)` for the pty and the tty, respectively. The new file descriptors are [non-inheritable](#fd-inheritance). For a (slightly) more portable approach, use the [`pty`](pty.xhtml#module-pty "pty: Pseudo-Terminal Handling for Linux. (Linux)") module. [可用性](intro.xhtml#availability): 某些 Unix。在 3.4 版更改: 新的文件描述符不再可繼承。 `os.``pipe`()Create a pipe. Return a pair of file descriptors `(r, w)` usable for reading and writing, respectively. The new file descriptor is [non-inheritable](#fd-inheritance). [可用性](intro.xhtml#availability): Unix, Windows。在 3.4 版更改: 新的文件描述符不再可繼承。 `os.``pipe2`(*flags*)Create a pipe with *flags* set atomically. *flags* can be constructed by ORing together one or more of these values: [`O_NONBLOCK`](#os.O_NONBLOCK "os.O_NONBLOCK"), [`O_CLOEXEC`](#os.O_CLOEXEC "os.O_CLOEXEC"). Return a pair of file descriptors `(r, w)` usable for reading and writing, respectively. [可用性](intro.xhtml#availability): 某些 Unix。 3\.3 新版功能. `os.``posix_fallocate`(*fd*, *offset*, *len*)Ensures that enough disk space is allocated for the file specified by *fd*starting from *offset* and continuing for *len* bytes. [可用性](intro.xhtml#availability): Unix。 3\.3 新版功能. `os.``posix_fadvise`(*fd*, *offset*, *len*, *advice*)Announces an intention to access data in a specific pattern thus allowing the kernel to make optimizations. The advice applies to the region of the file specified by *fd* starting at *offset* and continuing for *len* bytes. *advice* is one of [`POSIX_FADV_NORMAL`](#os.POSIX_FADV_NORMAL "os.POSIX_FADV_NORMAL"), [`POSIX_FADV_SEQUENTIAL`](#os.POSIX_FADV_SEQUENTIAL "os.POSIX_FADV_SEQUENTIAL"), [`POSIX_FADV_RANDOM`](#os.POSIX_FADV_RANDOM "os.POSIX_FADV_RANDOM"), [`POSIX_FADV_NOREUSE`](#os.POSIX_FADV_NOREUSE "os.POSIX_FADV_NOREUSE"), [`POSIX_FADV_WILLNEED`](#os.POSIX_FADV_WILLNEED "os.POSIX_FADV_WILLNEED") or [`POSIX_FADV_DONTNEED`](#os.POSIX_FADV_DONTNEED "os.POSIX_FADV_DONTNEED"). [可用性](intro.xhtml#availability): Unix。 3\.3 新版功能. `os.``POSIX_FADV_NORMAL``os.``POSIX_FADV_SEQUENTIAL``os.``POSIX_FADV_RANDOM``os.``POSIX_FADV_NOREUSE``os.``POSIX_FADV_WILLNEED``os.``POSIX_FADV_DONTNEED`Flags that can be used in *advice* in [`posix_fadvise()`](#os.posix_fadvise "os.posix_fadvise") that specify the access pattern that is likely to be used. [可用性](intro.xhtml#availability): Unix。 3\.3 新版功能. `os.``pread`(*fd*, *n*, *offset*)Read at most *n* bytes from file descriptor *fd* at a position of *offset*, leaving the file offset unchanged. 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. [可用性](intro.xhtml#availability): Unix。 3\.3 新版功能. `os.``preadv`(*fd*, *buffers*, *offset*, *flags=0*)Read from a file descriptor *fd* at a position of *offset* into mutable [bytes-like objects](../glossary.xhtml#term-bytes-like-object) *buffers*, leaving the file offset unchanged. 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. The flags argument contains a bitwise OR of zero or more of the following flags: - [`RWF_HIPRI`](#os.RWF_HIPRI "os.RWF_HIPRI") - [`RWF_NOWAIT`](#os.RWF_NOWAIT "os.RWF_NOWAIT") Return the total number of bytes actually read which can be less than the total capacity of all the objects. The operating system may set a limit ([`sysconf()`](#os.sysconf "os.sysconf") value `'SC_IOV_MAX'`) on the number of buffers that can be used. Combine the functionality of [`os.readv()`](#os.readv "os.readv") and [`os.pread()`](#os.pread "os.pread"). [Availability](intro.xhtml#availability): Linux 2.6.30 and newer, FreeBSD 6.0 and newer, OpenBSD 2.7 and newer. Using flags requires Linux 4.6 or newer. 3\.7 新版功能. `os.``RWF_NOWAIT`Do not wait for data which is not immediately available. If this flag is specified, the system call will return instantly if it would have to read data from the backing storage or wait for a lock. If some data was successfully read, it will return the number of bytes read. If no bytes were read, it will return `-1` and set errno to [`errno.EAGAIN`](errno.xhtml#errno.EAGAIN "errno.EAGAIN"). [Availability](intro.xhtml#availability): Linux 4.14 and newer. 3\.7 新版功能. `os.``RWF_HIPRI`High priority read/write. Allows block-based filesystems to use polling of the device, which provides lower latency, but may use additional resources. Currently, on Linux, this feature is usable only on a file descriptor opened using the [`O_DIRECT`](#os.O_DIRECT "os.O_DIRECT") flag. [Availability](intro.xhtml#availability): Linux 4.6 and newer. 3\.7 新版功能. `os.``pwrite`(*fd*, *str*, *offset*)Write the bytestring in *str* to file descriptor *fd* at position of *offset*, leaving the file offset unchanged. Return the number of bytes actually written. [可用性](intro.xhtml#availability): Unix。 3\.3 新版功能. `os.``pwritev`(*fd*, *buffers*, *offset*, *flags=0*)Write the *buffers* contents to file descriptor *fd* at a offset *offset*, leaving the file offset unchanged. *buffers* must be a sequence of [bytes-like objects](../glossary.xhtml#term-bytes-like-object). Buffers are processed in array order. Entire contents of the first buffer is written before proceeding to the second, and so on. The flags argument contains a bitwise OR of zero or more of the following flags: - [`RWF_DSYNC`](#os.RWF_DSYNC "os.RWF_DSYNC") - [`RWF_SYNC`](#os.RWF_SYNC "os.RWF_SYNC") Return the total number of bytes actually written. The operating system may set a limit ([`sysconf()`](#os.sysconf "os.sysconf") value `'SC_IOV_MAX'`) on the number of buffers that can be used. Combine the functionality of [`os.writev()`](#os.writev "os.writev") and [`os.pwrite()`](#os.pwrite "os.pwrite"). [Availability](intro.xhtml#availability): Linux 2.6.30 and newer, FreeBSD 6.0 and newer, OpenBSD 2.7 and newer. Using flags requires Linux 4.7 or newer. 3\.7 新版功能. `os.``RWF_DSYNC`Provide a per-write equivalent of the [`O_DSYNC`](#os.O_DSYNC "os.O_DSYNC")`open(2)` flag. This flag effect applies only to the data range written by the system call. [Availability](intro.xhtml#availability): Linux 4.7 and newer. 3\.7 新版功能. `os.``RWF_SYNC`Provide a per-write equivalent of the [`O_SYNC`](#os.O_SYNC "os.O_SYNC")`open(2)` flag. This flag effect applies only to the data range written by the system call. [Availability](intro.xhtml#availability): Linux 4.7 and newer. 3\.7 新版功能. `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. 注解 This function is intended for low-level I/O and must be applied to a file descriptor as returned by [`os.open()`](#os.open "os.open") or [`pipe()`](#os.pipe "os.pipe"). To read a "file object" returned by the built-in function [`open()`](functions.xhtml#open "open") or by [`popen()`](#os.popen "os.popen") or [`fdopen()`](#os.fdopen "os.fdopen"), or [`sys.stdin`](sys.xhtml#sys.stdin "sys.stdin"), use its `read()` or `readline()` methods. 在 3.5 版更改: 如果系統調用被中斷，但信號處理程序沒有觸發異常，此函數現在會重試系統調用，而不是觸發 [`InterruptedError`](exceptions.xhtml#InterruptedError "InterruptedError") 異常 (原因詳見 [**PEP 475**](https://www.python.org/dev/peps/pep-0475) \[https://www.python.org/dev/peps/pep-0475\])。 `os.``sendfile`(*out*, *in*, *offset*, *count*)`os.``sendfile`(*out*, *in*, *offset*, *count*, \[*headers*, \]\[*trailers*, \]*flags=0*)Copy *count* bytes from file descriptor *in* to file descriptor *out*starting at *offset*. Return the number of bytes sent. When EOF is reached return 0. The first function notation is supported by all platforms that define [`sendfile()`](#os.sendfile "os.sendfile"). On Linux, if *offset* is given as `None`, the bytes are read from the current position of *in* and the position of *in* is updated. The second case may be used on Mac OS X and FreeBSD where *headers* and *trailers* are arbitrary sequences of buffers that are written before and after the data from *in* is written. It returns the same as the first case. On Mac OS X and FreeBSD, a value of 0 for *count* specifies to send until the end of *in* is reached. All platforms support sockets as *out* file descriptor, and some platforms allow other types (e.g. regular file, pipe) as well. Cross-platform applications should not use *headers*, *trailers* and *flags*arguments. [可用性](intro.xhtml#availability): Unix。注解 For a higher-level wrapper of [`sendfile()`](#os.sendfile "os.sendfile"), see [`socket.socket.sendfile()`](socket.xhtml#socket.socket.sendfile "socket.socket.sendfile"). 3\.3 新版功能. `os.``set_blocking`(*fd*, *blocking*)Set the blocking mode of the specified file descriptor. Set the [`O_NONBLOCK`](#os.O_NONBLOCK "os.O_NONBLOCK") flag if blocking is `False`, clear the flag otherwise. See also [`get_blocking()`](#os.get_blocking "os.get_blocking") and [`socket.socket.setblocking()`](socket.xhtml#socket.socket.setblocking "socket.socket.setblocking"). [可用性](intro.xhtml#availability): Unix。 3\.5 新版功能. `os.``SF_NODISKIO``os.``SF_MNOWAIT``os.``SF_SYNC`Parameters to the [`sendfile()`](#os.sendfile "os.sendfile") function, if the implementation supports them. [可用性](intro.xhtml#availability): Unix。 3\.3 新版功能. `os.``readv`(*fd*, *buffers*)Read from a file descriptor *fd* into a number of mutable [bytes-like objects](../glossary.xhtml#term-bytes-like-object) *buffers*. 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. Return the total number of bytes actually read which can be less than the total capacity of all the objects. The operating system may set a limit ([`sysconf()`](#os.sysconf "os.sysconf") value `'SC_IOV_MAX'`) on the number of buffers that can be used. [可用性](intro.xhtml#availability): Unix。 3\.3 新版功能. `os.``tcgetpgrp`(*fd*)Return the process group associated with the terminal given by *fd* (an open file descriptor as returned by [`os.open()`](#os.open "os.open")). [可用性](intro.xhtml#availability): Unix。 `os.``tcsetpgrp`(*fd*, *pg*)Set the process group associated with the terminal given by *fd* (an open file descriptor as returned by [`os.open()`](#os.open "os.open")) to *pg*. [可用性](intro.xhtml#availability): Unix。 `os.``ttyname`(*fd*)Return a string which specifies the terminal device associated with file descriptor *fd*. If *fd* is not associated with a terminal device, an exception is raised. [可用性](intro.xhtml#availability): Unix。 `os.``write`(*fd*, *str*)Write the bytestring in *str* to file descriptor *fd*. Return the number of bytes actually written. 注解 This function is intended for low-level I/O and must be applied to a file descriptor as returned by [`os.open()`](#os.open "os.open") or [`pipe()`](#os.pipe "os.pipe"). To write a "file object" returned by the built-in function [`open()`](functions.xhtml#open "open") or by [`popen()`](#os.popen "os.popen") or [`fdopen()`](#os.fdopen "os.fdopen"), or [`sys.stdout`](sys.xhtml#sys.stdout "sys.stdout") or [`sys.stderr`](sys.xhtml#sys.stderr "sys.stderr"), use its `write()` method. 在 3.5 版更改: 如果系統調用被中斷，但信號處理程序沒有觸發異常，此函數現在會重試系統調用，而不是觸發 [`InterruptedError`](exceptions.xhtml#InterruptedError "InterruptedError") 異常 (原因詳見 [**PEP 475**](https://www.python.org/dev/peps/pep-0475) \[https://www.python.org/dev/peps/pep-0475\])。 `os.``writev`(*fd*, *buffers*)Write the contents of *buffers* to file descriptor *fd*. *buffers* must be a sequence of [bytes-like objects](../glossary.xhtml#term-bytes-like-object). Buffers are processed in array order. Entire contents of the first buffer is written before proceeding to the second, and so on. Returns the total number of bytes actually written. The operating system may set a limit ([`sysconf()`](#os.sysconf "os.sysconf") value `'SC_IOV_MAX'`) on the number of buffers that can be used. [可用性](intro.xhtml#availability): Unix。 3\.3 新版功能. ### Querying the size of a terminal 3\.3 新版功能. `os.``get_terminal_size`(*fd=STDOUT\_FILENO*)Return the size of the terminal window as `(columns, lines)`, tuple of type [`terminal_size`](#os.terminal_size "os.terminal_size"). The optional argument `fd` (default `STDOUT_FILENO`, or standard output) specifies which file descriptor should be queried. If the file descriptor is not connected to a terminal, an [`OSError`](exceptions.xhtml#OSError "OSError")is raised. [`shutil.get_terminal_size()`](shutil.xhtml#shutil.get_terminal_size "shutil.get_terminal_size") is the high-level function which should normally be used, `os.get_terminal_size` is the low-level implementation. [可用性](intro.xhtml#availability): Unix, Windows。 *class* `os.``terminal_size`A subclass of tuple, holding `(columns, lines)` of the terminal window size. `columns`Width of the terminal window in characters. `lines`Height of the terminal window in characters. ### Inheritance of File Descriptors 3\.4 新版功能. A file descriptor has an "inheritable" flag which indicates if the file descriptor can be inherited by child processes. Since Python 3.4, file descriptors created by Python are non-inheritable by default. On UNIX, non-inheritable file descriptors are closed in child processes at the execution of a new program, other file descriptors are inherited. On Windows, non-inheritable handles and file descriptors are closed in child processes, except for standard streams (file descriptors 0, 1 and 2: stdin, stdout and stderr), which are always inherited. Using [`spawn*`](#os.spawnl "os.spawnl") functions, all inheritable handles and all inheritable file descriptors are inherited. Using the [`subprocess`](subprocess.xhtml#module-subprocess "subprocess: Subprocess management.") module, all file descriptors except standard streams are closed, and inheritable handles are only inherited if the *close\_fds* parameter is `False`. `os.``get_inheritable`(*fd*)Get the "inheritable" flag of the specified file descriptor (a boolean). `os.``set_inheritable`(*fd*, *inheritable*)Set the "inheritable" flag of the specified file descriptor. `os.``get_handle_inheritable`(*handle*)Get the "inheritable" flag of the specified handle (a boolean). [可用性](intro.xhtml#availability): Windows。 `os.``set_handle_inheritable`(*handle*, *inheritable*)Set the "inheritable" flag of the specified handle. [可用性](intro.xhtml#availability): Windows。 ## Files and Directories On some Unix platforms, many of these functions support one or more of these features: - **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`](#os.supports_fd "os.supports_fd"). If it is unavailable, using it will raise a [`NotImplementedError`](exceptions.xhtml#NotImplementedError "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`](#os.supports_dir_fd "os.supports_dir_fd"). If it is unavailable, using it will raise a [`NotImplementedError`](exceptions.xhtml#NotImplementedError "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`](#os.supports_follow_symlinks "os.supports_follow_symlinks"). If it is unavailable, using it will raise a [`NotImplementedError`](exceptions.xhtml#NotImplementedError "NotImplementedError"). `os.``access`(*path*, *mode*, *\**, *dir\_fd=None*, *effective\_ids=False*, *follow\_symlinks=True*)Use the real uid/gid to test for access to *path*. Note that most operations will use the effective uid/gid, therefore this routine can be used in a suid/sgid environment to test if the invoking user has the specified access to *path*. *mode* should be [`F_OK`](#os.F_OK "os.F_OK") to test the existence of *path*, or it can be the inclusive OR of one or more of [`R_OK`](#os.R_OK "os.R_OK"), [`W_OK`](#os.W_OK "os.W_OK"), and [`X_OK`](#os.X_OK "os.X_OK") to test permissions. Return [`True`](constants.xhtml#True "True") if access is allowed, [`False`](constants.xhtml#False "False") if not. See the Unix man page *access(2)* for more information. This function can support specifying [paths relative to directory descriptors](#dir-fd) and [not following symlinks](#follow-symlinks). If *effective\_ids* is `True`, [`access()`](#os.access "os.access") will perform its access checks using the effective uid/gid instead of the real uid/gid. *effective\_ids* may not be supported on your platform; you can check whether or not it is available using [`os.supports_effective_ids`](#os.supports_effective_ids "os.supports_effective_ids"). If it is unavailable, using it will raise a [`NotImplementedError`](exceptions.xhtml#NotImplementedError "NotImplementedError"). 注解 Using [`access()`](#os.access "os.access") to check if a user is authorized to e.g. open a file before actually doing so using [`open()`](functions.xhtml#open "open") creates a security hole, because the user might exploit the short time interval between checking and opening the file to manipulate it. It's preferable to use [EAFP](../glossary.xhtml#term-eafp)techniques. For example: ``` if os.access("myfile", os.R_OK): with open("myfile") as fp: return fp.read() return "some default data" ``` is better written as: ``` try: fp = open("myfile") except PermissionError: return "some default data" else: with fp: return fp.read() ``` 注解 I/O operations may fail even when [`access()`](#os.access "os.access") indicates that they would succeed, particularly for operations on network filesystems which may have permissions semantics beyond the usual POSIX permission-bit model. 在 3.3 版更改: Added the *dir\_fd*, *effective\_ids*, and *follow\_symlinks* parameters. 在 3.6 版更改: 接受一個 [類路徑對象](../glossary.xhtml#term-path-like-object)。 `os.``F_OK``os.``R_OK``os.``W_OK``os.``X_OK`Values to pass as the *mode* parameter of [`access()`](#os.access "os.access") to test the existence, readability, writability and executability of *path*, respectively. `os.``chdir`(*path*)Change the current working directory to *path*. This function can support [specifying a file descriptor](#path-fd). The descriptor must refer to an opened directory, not an open file. 3\.3 新版功能: Added support for specifying *path* as a file descriptor on some platforms. 在 3.6 版更改: 接受一個 [類路徑對象](../glossary.xhtml#term-path-like-object)。 `os.``chflags`(*path*, *flags*, *\**, *follow\_symlinks=True*)Set the flags of *path* to the numeric *flags*. *flags* may take a combination (bitwise OR) of the following values (as defined in the [`stat`](stat.xhtml#module-stat "stat: Utilities for interpreting the results of os.stat(), os.lstat() and os.fstat().") module): - [`stat.UF_NODUMP`](stat.xhtml#stat.UF_NODUMP "stat.UF_NODUMP") - [`stat.UF_IMMUTABLE`](stat.xhtml#stat.UF_IMMUTABLE "stat.UF_IMMUTABLE") - [`stat.UF_APPEND`](stat.xhtml#stat.UF_APPEND "stat.UF_APPEND") - [`stat.UF_OPAQUE`](stat.xhtml#stat.UF_OPAQUE "stat.UF_OPAQUE") - [`stat.UF_NOUNLINK`](stat.xhtml#stat.UF_NOUNLINK "stat.UF_NOUNLINK") - [`stat.UF_COMPRESSED`](stat.xhtml#stat.UF_COMPRESSED "stat.UF_COMPRESSED") - [`stat.UF_HIDDEN`](stat.xhtml#stat.UF_HIDDEN "stat.UF_HIDDEN") - [`stat.SF_ARCHIVED`](stat.xhtml#stat.SF_ARCHIVED "stat.SF_ARCHIVED") - [`stat.SF_IMMUTABLE`](stat.xhtml#stat.SF_IMMUTABLE "stat.SF_IMMUTABLE") - [`stat.SF_APPEND`](stat.xhtml#stat.SF_APPEND "stat.SF_APPEND") - [`stat.SF_NOUNLINK`](stat.xhtml#stat.SF_NOUNLINK "stat.SF_NOUNLINK") - [`stat.SF_SNAPSHOT`](stat.xhtml#stat.SF_SNAPSHOT "stat.SF_SNAPSHOT") This function can support [not following symlinks](#follow-symlinks). [可用性](intro.xhtml#availability): Unix。 3\.3 新版功能: The *follow\_symlinks* argument. 在 3.6 版更改: 接受一個 [類路徑對象](../glossary.xhtml#term-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`](stat.xhtml#module-stat "stat: Utilities for interpreting the results of os.stat(), os.lstat() and os.fstat().") module) or bitwise ORed combinations of them: - [`stat.S_ISUID`](stat.xhtml#stat.S_ISUID "stat.S_ISUID") - [`stat.S_ISGID`](stat.xhtml#stat.S_ISGID "stat.S_ISGID") - [`stat.S_ENFMT`](stat.xhtml#stat.S_ENFMT "stat.S_ENFMT") - [`stat.S_ISVTX`](stat.xhtml#stat.S_ISVTX "stat.S_ISVTX") - [`stat.S_IREAD`](stat.xhtml#stat.S_IREAD "stat.S_IREAD") - [`stat.S_IWRITE`](stat.xhtml#stat.S_IWRITE "stat.S_IWRITE") - [`stat.S_IEXEC`](stat.xhtml#stat.S_IEXEC "stat.S_IEXEC") - [`stat.S_IRWXU`](stat.xhtml#stat.S_IRWXU "stat.S_IRWXU") - [`stat.S_IRUSR`](stat.xhtml#stat.S_IRUSR "stat.S_IRUSR") - [`stat.S_IWUSR`](stat.xhtml#stat.S_IWUSR "stat.S_IWUSR") - [`stat.S_IXUSR`](stat.xhtml#stat.S_IXUSR "stat.S_IXUSR") - [`stat.S_IRWXG`](stat.xhtml#stat.S_IRWXG "stat.S_IRWXG") - [`stat.S_IRGRP`](stat.xhtml#stat.S_IRGRP "stat.S_IRGRP") - [`stat.S_IWGRP`](stat.xhtml#stat.S_IWGRP "stat.S_IWGRP") - [`stat.S_IXGRP`](stat.xhtml#stat.S_IXGRP "stat.S_IXGRP") - [`stat.S_IRWXO`](stat.xhtml#stat.S_IRWXO "stat.S_IRWXO") - [`stat.S_IROTH`](stat.xhtml#stat.S_IROTH "stat.S_IROTH") - [`stat.S_IWOTH`](stat.xhtml#stat.S_IWOTH "stat.S_IWOTH") - [`stat.S_IXOTH`](stat.xhtml#stat.S_IXOTH "stat.S_IXOTH") This function can support [specifying a file descriptor](#path-fd), [paths relative to directory descriptors](#dir-fd) and [not following symlinks](#follow-symlinks). 注解 Although Windows supports [`chmod()`](#os.chmod "os.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 新版功能: Added support for specifying *path* as an open file descriptor, and the *dir\_fd* and *follow\_symlinks* arguments. 在 3.6 版更改: 接受一個 [類路徑對象](../glossary.xhtml#term-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](#path-fd), [paths relative to directory descriptors](#dir-fd) and [not following symlinks](#follow-symlinks). See [`shutil.chown()`](shutil.xhtml#shutil.chown "shutil.chown") for a higher-level function that accepts names in addition to numeric ids. [可用性](intro.xhtml#availability): Unix。 3\.3 新版功能: Added support for specifying an open file descriptor for *path*, and the *dir\_fd* and *follow\_symlinks* arguments. 在 3.6 版更改: Supports a [path-like object](../glossary.xhtml#term-path-like-object). `os.``chroot`(*path*)Change the root directory of the current process to *path*. [可用性](intro.xhtml#availability): Unix。在 3.6 版更改: 接受一個 [類路徑對象](../glossary.xhtml#term-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)`. [可用性](intro.xhtml#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()`](#os.chflags "os.chflags"), but do not follow symbolic links. As of Python 3.3, this is equivalent to `os.chflags(path, flags, follow_symlinks=False)`. [可用性](intro.xhtml#availability): Unix。在 3.6 版更改: 接受一個 [類路徑對象](../glossary.xhtml#term-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()`](#os.chmod "os.chmod")for possible values of *mode*. As of Python 3.3, this is equivalent to `os.chmod(path, mode, follow_symlinks=False)`. [可用性](intro.xhtml#availability): Unix。在 3.6 版更改: 接受一個 [類路徑對象](../glossary.xhtml#term-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)`. [可用性](intro.xhtml#availability): Unix。在 3.6 版更改: 接受一個 [類路徑對象](../glossary.xhtml#term-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](#dir-fd), and [not following symlinks](#follow-symlinks). [可用性](intro.xhtml#availability): Unix, Windows。在 3.2 版更改: Added Windows support. 3\.3 新版功能: Added the *src\_dir\_fd*, *dst\_dir\_fd*, and *follow\_symlinks* arguments. 在 3.6 版更改: Accepts a [path-like object](../glossary.xhtml#term-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](../glossary.xhtml#term-path-like-object). If *path* is of type `bytes`(directly or indirectly through the [`PathLike`](#os.PathLike "os.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](#path-fd); the file descriptor must refer to a directory. 注解 To encode `str` filenames to `bytes`, use [`fsencode()`](#os.fsencode "os.fsencode"). 參見 The [`scandir()`](#os.scandir "os.scandir") function returns directory entries along with file attribute information, giving better performance for many common use cases. 在 3.2 版更改: The *path* parameter became optional. 3\.3 新版功能: Added support for specifying an open file descriptor for *path*. 在 3.6 版更改: 接受一個 [類路徑對象](../glossary.xhtml#term-path-like-object)。 `os.``lstat`(*path*, *\**, *dir\_fd=None*)Perform the equivalent of an `lstat()` system call on the given path. Similar to [`stat()`](#os.stat "os.stat"), but does not follow symbolic links. Return a [`stat_result`](#os.stat_result "os.stat_result") object. On platforms that do not support symbolic links, this is an alias for [`stat()`](#os.stat "os.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](#dir-fd). 參見 [`stat()`](#os.stat "os.stat") 函數。在 3.2 版更改: Added support for Windows 6.0 (Vista) symbolic links. 在 3.3 版更改: Added the *dir\_fd* parameter. 在 3.6 版更改: Accepts a [path-like object](../glossary.xhtml#term-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`](exceptions.xhtml#FileExistsError "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()`](#os.chmod "os.chmod") explicitly to set them. This function can also support [paths relative to directory descriptors](#dir-fd). It is also possible to create temporary directories; see the [`tempfile`](tempfile.xhtml#module-tempfile "tempfile: Generate temporary files and directories.") module's [`tempfile.mkdtemp()`](tempfile.xhtml#tempfile.mkdtemp "tempfile.mkdtemp") function. 3\.3 新版功能: *dir\_fd* 參數。在 3.6 版更改: 接受一個 [類路徑對象](../glossary.xhtml#term-path-like-object)。 `os.``makedirs`(*name*, *mode=0o777*, *exist\_ok=False*)Recursive directory creation function. Like [`mkdir()`](#os.mkdir "os.mkdir"), but makes all intermediate-level directories needed to contain the leaf directory. The *mode* parameter is passed to [`mkdir()`](#os.mkdir "os.mkdir") for creating the leaf directory; see [the mkdir() description](#mkdir-modebits) for how it is interpreted. To set the file permission bits of any newly-created parent directories you can set the umask before invoking [`makedirs()`](#os.makedirs "os.makedirs"). The file permission bits of existing parent directories are not changed. If *exist\_ok* is `False` (the default), an [`OSError`](exceptions.xhtml#OSError "OSError") is raised if the target directory already exists. 注解 [`makedirs()`](#os.makedirs "os.makedirs") will become confused if the path elements to create include [`pardir`](#os.pardir "os.pardir") (eg. ".." on UNIX systems). This function handles UNC paths correctly. 3\.2 新版功能: The *exist\_ok* parameter. 在 3.4.1 版更改: Before Python 3.4.1, if *exist\_ok* was `True` and the directory existed, [`makedirs()`](#os.makedirs "os.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](https://bugs.python.org/issue21082) \[https://bugs.python.org/issue21082\]. 在 3.6 版更改: 接受一個 [類路徑對象](../glossary.xhtml#term-path-like-object)。在 3.7 版更改: The *mode* argument no longer affects the file permission bits of newly-created intermediate-level directories. `os.``mkfifo`(*path*, *mode=0o666*, *\**, *dir\_fd=None*)Create a FIFO (a named pipe) named *path* with numeric mode *mode*. The current umask value is first masked out from the mode. This function can also support [paths relative to directory descriptors](#dir-fd). FIFOs are pipes that can be accessed like regular files. FIFOs exist until they are deleted (for example with [`os.unlink()`](#os.unlink "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()`](#os.mkfifo "os.mkfifo")doesn't open the FIFO --- it just creates the rendezvous point. [可用性](intro.xhtml#availability): Unix。 3\.3 新版功能: *dir\_fd* 參數。在 3.6 版更改: 接受一個 [類路徑對象](../glossary.xhtml#term-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`](stat.xhtml#module-stat "stat: Utilities for interpreting the results of os.stat(), os.lstat() and os.fstat().")). For `stat.S_IFCHR` and `stat.S_IFBLK`, *device* defines the newly created device special file (probably using [`os.makedev()`](#os.makedev "os.makedev")), otherwise it is ignored. This function can also support [paths relative to directory descriptors](#dir-fd). [可用性](intro.xhtml#availability): Unix。 3\.3 新版功能: *dir\_fd* 參數。在 3.6 版更改: 接受一個 [類路徑對象](../glossary.xhtml#term-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. If *name* is a string and is not known, [`ValueError`](exceptions.xhtml#ValueError "ValueError") is raised. If a specific value for *name* is not supported by the host system, even if it is included in `pathconf_names`, an [`OSError`](exceptions.xhtml#OSError "OSError") is raised with [`errno.EINVAL`](errno.xhtml#errno.EINVAL "errno.EINVAL") for the error number. This function can support [specifying a file descriptor](#path-fd). [可用性](intro.xhtml#availability): Unix。在 3.6 版更改: 接受一個 [類路徑對象](../glossary.xhtml#term-path-like-object)。 `os.``pathconf_names`Dictionary mapping names accepted by [`pathconf()`](#os.pathconf "os.pathconf") and [`fpathconf()`](#os.fpathconf "os.fpathconf") to the integer values defined for those names by the host operating system. This can be used to determine the set of names known to the system. [可用性](intro.xhtml#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`](#os.PathLike "os.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](#dir-fd). [可用性](intro.xhtml#availability): Unix, Windows。在 3.2 版更改: Added support for Windows 6.0 (Vista) symbolic links. 3\.3 新版功能: *dir\_fd* 參數。在 3.6 版更改: 接受一個 [類路徑對象](../glossary.xhtml#term-path-like-object)。 `os.``remove`(*path*, *\**, *dir\_fd=None*)Remove (delete) the file *path*. If *path* is a directory, [`OSError`](exceptions.xhtml#OSError "OSError") is raised. Use [`rmdir()`](#os.rmdir "os.rmdir") to remove directories. This function can support [paths relative to directory descriptors](#dir-fd). 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()`](#os.unlink "os.unlink"). 3\.3 新版功能: *dir\_fd* 參數。在 3.6 版更改: 接受一個 [類路徑對象](../glossary.xhtml#term-path-like-object)。 `os.``removedirs`(*name*)Remove directories recursively. Works like [`rmdir()`](#os.rmdir "os.rmdir") except that, if the leaf directory is successfully removed, [`removedirs()`](#os.removedirs "os.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`](exceptions.xhtml#OSError "OSError") if the leaf directory could not be successfully removed. 在 3.6 版更改: 接受一個 [類路徑對象](../glossary.xhtml#term-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`](exceptions.xhtml#OSError "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`](exceptions.xhtml#OSError "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](#dir-fd). If you want cross-platform overwriting of the destination, use [`replace()`](#os.replace "os.replace"). 3\.3 新版功能: The *src\_dir\_fd* and *dst\_dir\_fd* arguments. 在 3.6 版更改: Accepts a [path-like object](../glossary.xhtml#term-path-like-object) for *src* and *dst*. `os.``renames`(*old*, *new*)Recursive directory or file renaming function. Works like [`rename()`](#os.rename "os.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()`](#os.removedirs "os.removedirs"). 注解 This function can fail with the new directory structure made if you lack permissions needed to remove the leaf directory or file. 在 3.6 版更改: Accepts a [path-like object](../glossary.xhtml#term-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`](exceptions.xhtml#OSError "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](#dir-fd). 3\.3 新版功能. 在 3.6 版更改: Accepts a [path-like object](../glossary.xhtml#term-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`](exceptions.xhtml#OSError "OSError") is raised. In order to remove whole directory trees, [`shutil.rmtree()`](shutil.xhtml#shutil.rmtree "shutil.rmtree") can be used. This function can support [paths relative to directory descriptors](#dir-fd). 3\.3 新版功能: The *dir\_fd* parameter. 在 3.6 版更改: 接受一個 [類路徑對象](../glossary.xhtml#term-path-like-object)。 `os.``scandir`(*path='.'*)Return an iterator of [`os.DirEntry`](#os.DirEntry "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()`](#os.scandir "os.scandir") instead of [`listdir()`](#os.listdir "os.listdir") can significantly increase the performance of code that also needs file type or file attribute information, because [`os.DirEntry`](#os.DirEntry "os.DirEntry") objects expose this information if the operating system provides it when scanning a directory. All [`os.DirEntry`](#os.DirEntry "os.DirEntry") methods may perform a system call, but [`is_dir()`](#os.DirEntry.is_dir "os.DirEntry.is_dir") and [`is_file()`](#os.DirEntry.is_file "os.DirEntry.is_file") usually only require a system call for symbolic links; [`os.DirEntry.stat()`](#os.DirEntry.stat "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](../glossary.xhtml#term-path-like-object). If *path* is of type `bytes`(directly or indirectly through the [`PathLike`](#os.PathLike "os.PathLike") interface), the type of the [`name`](#os.DirEntry.name "os.DirEntry.name") and [`path`](#os.DirEntry.path "os.DirEntry.path")attributes of each [`os.DirEntry`](#os.DirEntry "os.DirEntry") will be `bytes`; in all other circumstances, they will be of type `str`. This function can also support [specifying a file descriptor](#path-fd); the file descriptor must refer to a directory. The [`scandir()`](#os.scandir "os.scandir") iterator supports the [context manager](../glossary.xhtml#term-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`](../reference/compound_stmts.xhtml#with)statement. 3\.6 新版功能. The following example shows a simple use of [`scandir()`](#os.scandir "os.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) ``` 注解 On Unix-based systems, [`scandir()`](#os.scandir "os.scandir") uses the system's [opendir()](http://pubs.opengroup.org/onlinepubs/009695399/functions/opendir.html) \[http://pubs.opengroup.org/onlinepubs/009695399/functions/opendir.html\]and [readdir()](http://pubs.opengroup.org/onlinepubs/009695399/functions/readdir_r.html) \[http://pubs.opengroup.org/onlinepubs/009695399/functions/readdir\_r.html\]functions. On Windows, it uses the Win32 [FindFirstFileW](https://msdn.microsoft.com/en-us/library/windows/desktop/aa364418(v=vs.85).aspx) \[https://msdn.microsoft.com/en-us/library/windows/desktop/aa364418(v=vs.85).aspx\]and [FindNextFileW](https://msdn.microsoft.com/en-us/library/windows/desktop/aa364428(v=vs.85).aspx) \[https://msdn.microsoft.com/en-us/library/windows/desktop/aa364428(v=vs.85).aspx\]functions. 3\.5 新版功能. 3\.6 新版功能: Added support for the [context manager](../glossary.xhtml#term-context-manager) protocol and the [`close()`](#os.scandir.close "os.scandir.close") method. If a [`scandir()`](#os.scandir "os.scandir") iterator is neither exhausted nor explicitly closed a [`ResourceWarning`](exceptions.xhtml#ResourceWarning "ResourceWarning") will be emitted in its destructor. The function accepts a [path-like object](../glossary.xhtml#term-path-like-object). 在 3.7 版更改: Added support for [file descriptors](#path-fd) on Unix. *class* `os.``DirEntry`Object yielded by [`scandir()`](#os.scandir "os.scandir") to expose the file path and other file attributes of a directory entry. [`scandir()`](#os.scandir "os.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()`](#os.scandir "os.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`](exceptions.xhtml#OSError "OSError"). If you need very fine-grained control over errors, you can catch [`OSError`](exceptions.xhtml#OSError "OSError") when calling one of the `os.DirEntry` methods and handle as appropriate. To be directly usable as a [path-like object](../glossary.xhtml#term-path-like-object), `os.DirEntry`implements the [`PathLike`](#os.PathLike "os.PathLike") interface. Attributes and methods on a `os.DirEntry` instance are as follows: `name`The entry's base filename, relative to the [`scandir()`](#os.scandir "os.scandir") *path*argument. The [`name`](#os.name "os.name") attribute will be `bytes` if the [`scandir()`](#os.scandir "os.scandir")*path* argument is of type `bytes` and `str` otherwise. Use [`fsdecode()`](#os.fsdecode "os.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()`](#os.scandir "os.scandir") *path*argument. The path is only absolute if the [`scandir()`](#os.scandir "os.scandir") *path*argument was absolute. If the [`scandir()`](#os.scandir "os.scandir") *path*argument was a [file descriptor](#path-fd), the [`path`](os.path.xhtml#module-os.path "os.path: Operations on pathnames.")attribute is the same as the [`name`](#os.name "os.name") attribute. The [`path`](os.path.xhtml#module-os.path "os.path: Operations on pathnames.") attribute will be `bytes` if the [`scandir()`](#os.scandir "os.scandir")*path* argument is of type `bytes` and `str` otherwise. Use [`fsdecode()`](#os.fsdecode "os.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()`](#os.stat "os.stat") along with [`stat.S_ISDIR()`](stat.xhtml#stat.S_ISDIR "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`](exceptions.xhtml#OSError "OSError"), such as [`PermissionError`](exceptions.xhtml#PermissionError "PermissionError"), but [`FileNotFoundError`](exceptions.xhtml#FileNotFoundError "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()`](#os.DirEntry.is_dir "os.DirEntry.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()`](os.path.xhtml#os.path.islink "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`](exceptions.xhtml#OSError "OSError"), such as [`PermissionError`](exceptions.xhtml#PermissionError "PermissionError"), but [`FileNotFoundError`](exceptions.xhtml#FileNotFoundError "FileNotFoundError") is caught and not raised. `stat`(*\**, *follow\_symlinks=True*)Return a [`stat_result`](#os.stat_result "os.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`](#os.stat_result "os.stat_result") are always set to zero. Call [`os.stat()`](#os.stat "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()`](#os.stat "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`](pathlib.xhtml#pathlib.Path "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 新版功能. 在 3.6 版更改: Added support for the [`PathLike`](#os.PathLike "os.PathLike") interface. Added support for [`bytes`](stdtypes.xhtml#bytes "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`](#os.PathLike "os.PathLike")interface -- or as an open file descriptor. Return a [`stat_result`](#os.stat_result "os.stat_result")object. This function normally follows symlinks; to stat a symlink add the argument `follow_symlinks=False`, or use [`lstat()`](#os.lstat "os.lstat"). This function can support [specifying a file descriptor](#path-fd) and [not following symlinks](#follow-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 ``` 參見 [`fstat()`](#os.fstat "os.fstat") and [`lstat()`](#os.lstat "os.lstat") functions. 3\.3 新版功能: Added the *dir\_fd* and *follow\_symlinks* arguments, specifying a file descriptor instead of a path. 在 3.6 版更改: 接受一個 [類路徑對象](../glossary.xhtml#term-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.stat "os.stat"), [`os.fstat()`](#os.fstat "os.fstat") and [`os.lstat()`](#os.lstat "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](https://msdn.microsoft.com/en-us/library/aa363788) \[https://msdn.microsoft.com/en-us/library/aa363788\] 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. 注解 The exact meaning and resolution of the [`st_atime`](#os.stat_result.st_atime "os.stat_result.st_atime"), [`st_mtime`](#os.stat_result.st_mtime "os.stat_result.st_mtime"), and [`st_ctime`](#os.stat_result.st_ctime "os.stat_result.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`](#os.stat_result.st_mtime "os.stat_result.st_mtime") has 2-second resolution, and [`st_atime`](#os.stat_result.st_atime "os.stat_result.st_atime") has only 1-day resolution. See your operating system documentation for details. Similarly, although [`st_atime_ns`](#os.stat_result.st_atime_ns "os.stat_result.st_atime_ns"), [`st_mtime_ns`](#os.stat_result.st_mtime_ns "os.stat_result.st_mtime_ns"), and [`st_ctime_ns`](#os.stat_result.st_ctime_ns "os.stat_result.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`](#os.stat_result.st_atime "os.stat_result.st_atime"), [`st_mtime`](#os.stat_result.st_mtime "os.stat_result.st_mtime"), and [`st_ctime`](#os.stat_result.st_ctime "os.stat_result.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`](#os.stat_result.st_atime_ns "os.stat_result.st_atime_ns"), [`st_mtime_ns`](#os.stat_result.st_mtime_ns "os.stat_result.st_mtime_ns"), and [`st_ctime_ns`](#os.stat_result.st_ctime_ns "os.stat_result.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`](#os.stat_result.st_size "os.stat_result.st_size")/512 when the file has holes. `st_blksize`"Preferred" blocksize for efficient file system I/O. Writing to a file in smaller chunks may cause an inefficient read-modify-rewrite. `st_rdev`Type of device if an inode device. `st_flags`User defined flags for file. On other Unix systems (such as FreeBSD), the following attributes may be available (but may be only filled out if root tries to use them): `st_gen`File generation number. `st_birthtime`Time of file creation. On Solaris and derivatives, the following attributes may also be available: `st_fstype`String that uniquely identifies the type of the filesystem that contains the file. On Mac OS systems, the following attributes may also be available: `st_rsize`Real size of the file. `st_creator`Creator of the file. `st_type`File type. On Windows systems, the following 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`](stat.xhtml#module-stat "stat: Utilities for interpreting the results of os.stat(), os.lstat() and os.fstat().") module. The standard module [`stat`](stat.xhtml#module-stat "stat: Utilities for interpreting the results of os.stat(), os.lstat() and os.fstat().") 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`](#os.stat_result "os.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`](#os.stat_result.st_mode "os.stat_result.st_mode"), [`st_ino`](#os.stat_result.st_ino "os.stat_result.st_ino"), [`st_dev`](#os.stat_result.st_dev "os.stat_result.st_dev"), [`st_nlink`](#os.stat_result.st_nlink "os.stat_result.st_nlink"), [`st_uid`](#os.stat_result.st_uid "os.stat_result.st_uid"), [`st_gid`](#os.stat_result.st_gid "os.stat_result.st_gid"), [`st_size`](#os.stat_result.st_size "os.stat_result.st_size"), [`st_atime`](#os.stat_result.st_atime "os.stat_result.st_atime"), [`st_mtime`](#os.stat_result.st_mtime "os.stat_result.st_mtime"), [`st_ctime`](#os.stat_result.st_ctime "os.stat_result.st_ctime"). More items may be added at the end by some implementations. For compatibility with older Python versions, accessing [`stat_result`](#os.stat_result "os.stat_result") as a tuple always returns integers. 3\.3 新版功能: Added the [`st_atime_ns`](#os.stat_result.st_atime_ns "os.stat_result.st_atime_ns"), [`st_mtime_ns`](#os.stat_result.st_mtime_ns "os.stat_result.st_mtime_ns"), and [`st_ctime_ns`](#os.stat_result.st_ctime_ns "os.stat_result.st_ctime_ns") members. 3\.5 新版功能: Added the [`st_file_attributes`](#os.stat_result.st_file_attributes "os.stat_result.st_file_attributes") member on Windows. 在 3.5 版更改: Windows now returns the file index as [`st_ino`](#os.stat_result.st_ino "os.stat_result.st_ino") when available. 3\.7 新版功能: Added the [`st_fstype`](#os.stat_result.st_fstype "os.stat_result.st_fstype") member to Solaris/derivatives. `os.``statvfs`(*path*)Perform a `statvfs()` system call on the given path. The return value is an object whose attributes describe the filesystem on the given path, and correspond to the members of the `statvfs` structure, namely: `f_bsize`, `f_frsize`, `f_blocks`, `f_bfree`, `f_bavail`, `f_files`, `f_ffree`, `f_favail`, `f_flag`, `f_namemax`, `f_fsid`. Two module-level constants are defined for the `f_flag` attribute's bit-flags: if `ST_RDONLY` is set, the filesystem is mounted read-only, and if `ST_NOSUID` is set, the semantics of setuid/setgid bits are disabled or not supported. Additional module-level constants are defined for GNU/glibc based systems. These are `ST_NODEV` (disallow access to device special files), `ST_NOEXEC` (disallow program execution), `ST_SYNCHRONOUS`(writes are synced at once), `ST_MANDLOCK` (allow mandatory locks on an FS), `ST_WRITE` (write on file/directory/symlink), `ST_APPEND`(append-only file), `ST_IMMUTABLE` (immutable file), `ST_NOATIME`(do not update access times), `ST_NODIRATIME` (do not update directory access times), `ST_RELATIME` (update atime relative to mtime/ctime). This function can support [specifying a file descriptor](#path-fd). [可用性](intro.xhtml#availability): Unix。在 3.2 版更改: The `ST_RDONLY` and `ST_NOSUID` constants were added. 3\.3 新版功能: Added support for specifying an open file descriptor for *path*. 在 3.4 版更改: 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. 在 3.6 版更改: 接受一個 [類路徑對象](../glossary.xhtml#term-path-like-object)。 3\.7 新版功能: Added `f_fsid`. `os.``supports_dir_fd`A [`Set`](collections.abc.xhtml#collections.abc.Set "collections.abc.Set") object indicating which functions in the [`os`](#module-os "os: Miscellaneous operating system interfaces.") 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()`](#os.stat "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 新版功能. `os.``supports_effective_ids`A [`Set`](collections.abc.xhtml#collections.abc.Set "collections.abc.Set") object indicating which functions in the [`os`](#module-os "os: Miscellaneous operating system interfaces.") module permit use of the *effective\_ids* parameter for [`os.access()`](#os.access "os.access"). If the local platform supports it, the collection will contain [`os.access()`](#os.access "os.access"), otherwise it will be empty. To check whether you can use the *effective\_ids* parameter for [`os.access()`](#os.access "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 新版功能. `os.``supports_fd`A [`Set`](collections.abc.xhtml#collections.abc.Set "collections.abc.Set") object indicating which functions in the [`os`](#module-os "os: Miscellaneous operating system interfaces.") 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()`](#os.chdir "os.chdir") accepts open file descriptors when called on your local platform: ``` os.chdir in os.supports_fd ``` 3\.3 新版功能. `os.``supports_follow_symlinks`A [`Set`](collections.abc.xhtml#collections.abc.Set "collections.abc.Set") object indicating which functions in the [`os`](#module-os "os: Miscellaneous operating system interfaces.") 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()`](#os.stat "os.stat") is locally available: ``` os.stat in os.supports_follow_symlinks ``` 3\.3 新版功能. `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()`](#os.symlink "os.symlink")will raise a [`NotImplementedError`](exceptions.xhtml#NotImplementedError "NotImplementedError") on Windows versions earlier than 6.0. This function can support [paths relative to directory descriptors](#dir-fd). 注解 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`](exceptions.xhtml#OSError "OSError") is raised when the function is called by an unprivileged user. [可用性](intro.xhtml#availability): Unix, Windows。在 3.2 版更改: Added support for Windows 6.0 (Vista) symbolic links. 3\.3 新版功能: Added the *dir\_fd* argument, and now allow *target\_is\_directory*on non-Windows platforms. 在 3.6 版更改: Accepts a [path-like object](../glossary.xhtml#term-path-like-object) for *src* and *dst*. `os.``sync`()Force write of everything to disk. [可用性](intro.xhtml#availability): Unix。 3\.3 新版功能. `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](#path-fd). [可用性](intro.xhtml#availability): Unix, Windows。 3\.3 新版功能. 在 3.5 版更改: 添加了 Windows 支持在 3.6 版更改: 接受一個 [類路徑對象](../glossary.xhtml#term-path-like-object)。 `os.``unlink`(*path*, *\**, *dir\_fd=None*)Remove (delete) the file *path*. This function is semantically identical to [`remove()`](#os.remove "os.remove"); the `unlink` name is its traditional Unix name. Please see the documentation for [`remove()`](#os.remove "os.remove") for further information. 3\.3 新版功能: The *dir\_fd* parameter. 在 3.6 版更改: 接受一個 [類路徑對象](../glossary.xhtml#term-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()`](#os.utime "os.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()`](#os.stat "os.stat") call, depending on the resolution with which your operating system records access and modification times; see [`stat()`](#os.stat "os.stat"). The best way to preserve exact times is to use the *st\_atime\_ns* and *st\_mtime\_ns* fields from the [`os.stat()`](#os.stat "os.stat")result object with the *ns* parameter to utime. This function can support [specifying a file descriptor](#path-fd), [paths relative to directory descriptors](#dir-fd) and [not following symlinks](#follow-symlinks). 3\.3 新版功能: Added support for specifying an open file descriptor for *path*, and the *dir\_fd*, *follow\_symlinks*, and *ns* parameters. 在 3.6 版更改: 接受一個 [類路徑對象](../glossary.xhtml#term-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`](../reference/simple_stmts.xhtml#del) or slice assignment), and [`walk()`](#os.walk "os.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()`](#os.walk "os.walk") about directories the caller creates or renames before it resumes [`walk()`](#os.walk "os.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()`](#os.scandir "os.scandir") call are ignored. If optional argument *onerror* is specified, it should be a function; it will be called with one argument, an [`OSError`](exceptions.xhtml#OSError "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()`](#os.walk "os.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. 注解 Be aware that setting *followlinks* to `True` can lead to infinite recursion if a link points to a parent directory of itself. [`walk()`](#os.walk "os.walk")does not keep track of the directories it visited already. 注解 If you pass a relative pathname, don't change the current working directory between resumptions of [`walk()`](#os.walk "os.walk"). [`walk()`](#os.walk "os.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()`](shutil.xhtml#shutil.rmtree "shutil.rmtree")), walking the tree bottom-up is essential, [`rmdir()`](#os.rmdir "os.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)) ``` 在 3.5 版更改: This function now calls [`os.scandir()`](#os.scandir "os.scandir") instead of [`os.listdir()`](#os.listdir "os.listdir"), making it faster by reducing the number of calls to [`os.stat()`](#os.stat "os.stat"). 在 3.6 版更改: 接受一個 [類路徑對象](../glossary.xhtml#term-path-like-object)。 `os.``fwalk`(*top='.'*, *topdown=True*, *onerror=None*, *\**, *follow\_symlinks=False*, *dir\_fd=None*)This behaves exactly like [`walk()`](#os.walk "os.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()`](#os.walk "os.walk") output, and *dirfd* is a file descriptor referring to the directory *dirpath*. This function always supports [paths relative to directory descriptors](#dir-fd) and [not following symlinks](#follow-symlinks). Note however that, unlike other functions, the [`fwalk()`](#os.fwalk "os.fwalk") default value for *follow\_symlinks* is `False`. 注解 Since [`fwalk()`](#os.fwalk "os.fwalk") yields file descriptors, those are only valid until the next iteration step, so you should duplicate them (e.g. with [`dup()`](#os.dup "os.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()`](#os.rmdir "os.rmdir") doesn't allow deleting a directory before the directory is empty: ``` # Delete everything reachable from the directory named in "top", # assuming there are no symbolic links. # CAUTION: This is dangerous! For example, if top == '/', it # could delete all your disk files. import os for root, dirs, files, rootfd in os.fwalk(top, topdown=False): for name in files: os.unlink(name, dir_fd=rootfd) for name in dirs: os.rmdir(name, dir_fd=rootfd) ``` [可用性](intro.xhtml#availability): Unix。 3\.3 新版功能. 在 3.6 版更改: 接受一個 [類路徑對象](../glossary.xhtml#term-path-like-object)。在 3.7 版更改: Added support for [`bytes`](stdtypes.xhtml#bytes "bytes") paths. ### Linux extended attributes 3\.3 新版功能. 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`](#os.PathLike "os.PathLike") interface). If it is str, it is encoded with the filesystem encoding. This function can support [specifying a file descriptor](#path-fd) and [not following symlinks](#follow-symlinks). 在 3.6 版更改: Accepts a [path-like object](../glossary.xhtml#term-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()`](#os.listxattr "os.listxattr") will examine the current directory. This function can support [specifying a file descriptor](#path-fd) and [not following symlinks](#follow-symlinks). 在 3.6 版更改: 接受一個 [類路徑對象](../glossary.xhtml#term-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`](#os.PathLike "os.PathLike") interface). If it is a string, it is encoded with the filesystem encoding. This function can support [specifying a file descriptor](#path-fd) and [not following symlinks](#follow-symlinks). 在 3.6 版更改: Accepts a [path-like object](../glossary.xhtml#term-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`](#os.PathLike "os.PathLike") interface). If it is a str, it is encoded with the filesystem encoding. *flags* may be [`XATTR_REPLACE`](#os.XATTR_REPLACE "os.XATTR_REPLACE") or [`XATTR_CREATE`](#os.XATTR_CREATE "os.XATTR_CREATE"). If [`XATTR_REPLACE`](#os.XATTR_REPLACE "os.XATTR_REPLACE") is given and the attribute does not exist, `EEXISTS` will be raised. If [`XATTR_CREATE`](#os.XATTR_CREATE "os.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](#path-fd) and [not following symlinks](#follow-symlinks). 注解 A bug in Linux kernel versions less than 2.6.39 caused the flags argument to be ignored on some filesystems. 在 3.6 版更改: Accepts a [path-like object](../glossary.xhtml#term-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()`](#os.setxattr "os.setxattr"). It indicates the operation must create an attribute. `os.``XATTR_REPLACE`This is a possible value for the flags argument in [`setxattr()`](#os.setxattr "os.setxattr"). It indicates the operation must replace an existing attribute. ## Process Management These functions may be used to create and manage processes. The various [`exec*`](#os.execl "os.execl") 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()`](signal.xhtml#signal.signal "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.xhtml#OSError "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()`](#os.fsync "os.fsync") before calling an [`exec*`](#os.execl "os.execl") function. The "l" and "v" variants of the [`exec*`](#os.execl "os.execl") 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()`](#os.execlp "os.execlp"), [`execlpe()`](#os.execlpe "os.execlpe"), [`execvp()`](#os.execvp "os.execvp"), and [`execvpe()`](#os.execvpe "os.execvpe")) will use the `PATH` environment variable to locate the program *file*. When the environment is being replaced (using one of the [`exec*e`](#os.execl "os.execl") variants, discussed in the next paragraph), the new environment is used as the source of the `PATH` variable. The other variants, [`execl()`](#os.execl "os.execl"), [`execle()`](#os.execle "os.execle"), [`execv()`](#os.execv "os.execv"), and [`execve()`](#os.execve "os.execve"), will not use the `PATH` variable to locate the executable; *path* must contain an appropriate absolute or relative path. For [`execle()`](#os.execle "os.execle"), [`execlpe()`](#os.execlpe "os.execlpe"), [`execve()`](#os.execve "os.execve"), and [`execvpe()`](#os.execvpe "os.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()`](#os.execl "os.execl"), [`execlp()`](#os.execlp "os.execlp"), [`execv()`](#os.execv "os.execv"), and [`execvp()`](#os.execvp "os.execvp") all cause the new process to inherit the environment of the current process. For [`execve()`](#os.execve "os.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`](#os.supports_fd "os.supports_fd"). If it is unavailable, using it will raise a [`NotImplementedError`](exceptions.xhtml#NotImplementedError "NotImplementedError"). [可用性](intro.xhtml#availability): Unix, Windows。 3\.3 新版功能: Added support for specifying an open file descriptor for *path*for [`execve()`](#os.execve "os.execve"). 在 3.6 版更改: 接受一個 [類路徑對象](../glossary.xhtml#term-path-like-object)。 `os.``_exit`(*n*)Exit the process with status *n*, without calling cleanup handlers, flushing stdio buffers, etc. 注解 The standard way to exit is `sys.exit(n)`. [`_exit()`](#os._exit "os._exit") should normally only be used in the child process after a [`fork()`](#os.fork "os.fork"). The following exit codes are defined and can be used with [`_exit()`](#os._exit "os._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. 注解 Some of these may not be available on all Unix platforms, since there is some variation. These constants are defined where they are defined by the underlying platform. `os.``EX_OK`Exit code that means no error occurred. [可用性](intro.xhtml#availability): Unix。 `os.``EX_USAGE`Exit code that means the command was used incorrectly, such as when the wrong number of arguments are given. [可用性](intro.xhtml#availability): Unix。 `os.``EX_DATAERR`Exit code that means the input data was incorrect. [可用性](intro.xhtml#availability): Unix。 `os.``EX_NOINPUT`Exit code that means an input file did not exist or was not readable. [可用性](intro.xhtml#availability): Unix。 `os.``EX_NOUSER`Exit code that means a specified user did not exist. [可用性](intro.xhtml#availability): Unix。 `os.``EX_NOHOST`Exit code that means a specified host did not exist. [可用性](intro.xhtml#availability): Unix。 `os.``EX_UNAVAILABLE`Exit code that means that a required service is unavailable. [可用性](intro.xhtml#availability): Unix。 `os.``EX_SOFTWARE`Exit code that means an internal software error was detected. [可用性](intro.xhtml#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. [可用性](intro.xhtml#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. [可用性](intro.xhtml#availability): Unix。 `os.``EX_CANTCREAT`Exit code that means a user specified output file could not be created. [可用性](intro.xhtml#availability): Unix。 `os.``EX_IOERR`Exit code that means that an error occurred while doing I/O on some file. [可用性](intro.xhtml#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. [可用性](intro.xhtml#availability): Unix。 `os.``EX_PROTOCOL`Exit code that means that a protocol exchange was illegal, invalid, or not understood. [可用性](intro.xhtml#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). [可用性](intro.xhtml#availability): Unix。 `os.``EX_CONFIG`Exit code that means that some kind of configuration error occurred. [可用性](intro.xhtml#availability): Unix。 `os.``EX_NOTFOUND`Exit code that means something like "an entry was not found". [可用性](intro.xhtml#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`](exceptions.xhtml#OSError "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`](ssl.xhtml#module-ssl "ssl: TLS/SSL wrapper for socket objects") for applications that use the SSL module with fork(). [可用性](intro.xhtml#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`](pty.xhtml#module-pty "pty: Pseudo-Terminal Handling for Linux. (Linux)") module. If an error occurs [`OSError`](exceptions.xhtml#OSError "OSError") is raised. [可用性](intro.xhtml#availability): 某些 Unix。 `os.``kill`(*pid*, *sig*)Send signal *sig* to the process *pid*. Constants for the specific signals available on the host platform are defined in the [`signal`](signal.xhtml#module-signal "signal: Set handlers for asynchronous events.") module. Windows: The [`signal.CTRL_C_EVENT`](signal.xhtml#signal.CTRL_C_EVENT "signal.CTRL_C_EVENT") and [`signal.CTRL_BREAK_EVENT`](signal.xhtml#signal.CTRL_BREAK_EVENT "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()`](#os.kill "os.kill") additionally takes process handles to be killed. See also [`signal.pthread_kill()`](signal.xhtml#signal.pthread_kill "signal.pthread_kill"). 3\.2 新版功能: Windows support. `os.``killpg`(*pgid*, *sig*)Send the signal *sig* to the process group *pgid*. [可用性](intro.xhtml#availability): Unix。 `os.``nice`(*increment*)Add *increment* to the process's "niceness". Return the new niceness. [可用性](intro.xhtml#availability): Unix。 `os.``plock`(*op*)Lock program segments into memory. The value of *op* (defined in `<sys/lock.h>`) determines which segments are locked. [可用性](intro.xhtml#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()`](functions.xhtml#open "open") function. The returned file object reads or writes text strings rather than bytes. The `close` method returns [`None`](constants.xhtml#None "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`](subprocess.xhtml#subprocess.Popen "subprocess.Popen"); see that class's documentation for more powerful ways to manage and communicate with subprocesses. `os.``register_at_fork`(*\**, *before=None*, *after\_in\_parent=None*, *after\_in\_child=None*)Register callables to be executed when a new child process is forked using [`os.fork()`](#os.fork "os.fork") or similar process cloning APIs. The parameters are optional and keyword-only. Each specifies a different call point. - *before* is a function called before forking a child process. - *after\_in\_parent* is a function called from the parent process after forking a child process. - *after\_in\_child* is a function called from the child process. These calls are only made if control is expected to return to the Python interpreter. A typical [`subprocess`](subprocess.xhtml#module-subprocess "subprocess: Subprocess management.") launch will not trigger them as the child is not going to re-enter the interpreter. Functions registered for execution before forking are called in reverse registration order. Functions registered for execution after forking (either in the parent or in the child) are called in registration order. Note that `fork()` calls made by third-party C code may not call those functions, unless it explicitly calls [`PyOS_BeforeFork()`](../c-api/sys.xhtml#c.PyOS_BeforeFork "PyOS_BeforeFork"), [`PyOS_AfterFork_Parent()`](../c-api/sys.xhtml#c.PyOS_AfterFork_Parent "PyOS_AfterFork_Parent") and [`PyOS_AfterFork_Child()`](../c-api/sys.xhtml#c.PyOS_AfterFork_Child "PyOS_AfterFork_Child"). There is no way to unregister a function. [可用性](intro.xhtml#availability): Unix。 3\.7 新版功能. `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`](subprocess.xhtml#module-subprocess "subprocess: Subprocess management.") 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](subprocess.xhtml#subprocess-replacements) section.) If *mode* is [`P_NOWAIT`](#os.P_NOWAIT "os.P_NOWAIT"), this function returns the process id of the new process; if *mode* is [`P_WAIT`](#os.P_WAIT "os.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()`](#os.waitpid "os.waitpid") function. The "l" and "v" variants of the [`spawn*`](#os.spawnl "os.spawnl") 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()`](#os.spawnlp "os.spawnlp"), [`spawnlpe()`](#os.spawnlpe "os.spawnlpe"), [`spawnvp()`](#os.spawnvp "os.spawnvp"), and [`spawnvpe()`](#os.spawnvpe "os.spawnvpe")) will use the `PATH` environment variable to locate the program *file*. When the environment is being replaced (using one of the [`spawn*e`](#os.spawnl "os.spawnl") variants, discussed in the next paragraph), the new environment is used as the source of the `PATH` variable. The other variants, [`spawnl()`](#os.spawnl "os.spawnl"), [`spawnle()`](#os.spawnle "os.spawnle"), [`spawnv()`](#os.spawnv "os.spawnv"), and [`spawnve()`](#os.spawnve "os.spawnve"), will not use the `PATH` variable to locate the executable; *path* must contain an appropriate absolute or relative path. For [`spawnle()`](#os.spawnle "os.spawnle"), [`spawnlpe()`](#os.spawnlpe "os.spawnlpe"), [`spawnve()`](#os.spawnve "os.spawnve"), and [`spawnvpe()`](#os.spawnvpe "os.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()`](#os.spawnl "os.spawnl"), [`spawnlp()`](#os.spawnlp "os.spawnlp"), [`spawnv()`](#os.spawnv "os.spawnv"), and [`spawnvp()`](#os.spawnvp "os.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()`](#os.spawnlp "os.spawnlp") and [`spawnvpe()`](#os.spawnvpe "os.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](intro.xhtml#availability): Unix, Windows. [`spawnlp()`](#os.spawnlp "os.spawnlp"), [`spawnlpe()`](#os.spawnlpe "os.spawnlpe"), [`spawnvp()`](#os.spawnvp "os.spawnvp")and [`spawnvpe()`](#os.spawnvpe "os.spawnvpe") are not available on Windows. [`spawnle()`](#os.spawnle "os.spawnle") and [`spawnve()`](#os.spawnve "os.spawnve") are not thread-safe on Windows; we advise you to use the [`subprocess`](subprocess.xhtml#module-subprocess "subprocess: Subprocess management.") module instead. 在 3.6 版更改: 接受一個 [類路徑對象](../glossary.xhtml#term-path-like-object)。 `os.``P_NOWAIT``os.``P_NOWAITO`Possible values for the *mode* parameter to the [`spawn*`](#os.spawnl "os.spawnl") family of functions. If either of these values is given, the `spawn*()` functions will return as soon as the new process has been created, with the process id as the return value. [可用性](intro.xhtml#availability): Unix, Windows。 `os.``P_WAIT`Possible value for the *mode* parameter to the [`spawn*`](#os.spawnl "os.spawnl") family of functions. If this is given as *mode*, the `spawn*()` functions will not return until the new process has run to completion and will return the exit code of the process the run is successful, or `-signal` if a signal kills the process. [可用性](intro.xhtml#availability): Unix, Windows。 `os.``P_DETACH``os.``P_OVERLAY`Possible values for the *mode* parameter to the [`spawn*`](#os.spawnl "os.spawnl") family of functions. These are less portable than those listed above. [`P_DETACH`](#os.P_DETACH "os.P_DETACH")is similar to [`P_NOWAIT`](#os.P_NOWAIT "os.P_NOWAIT"), but the new process is detached from the console of the calling process. If [`P_OVERLAY`](#os.P_OVERLAY "os.P_OVERLAY") is used, the current process will be replaced; the [`spawn*`](#os.spawnl "os.spawnl") function will not return. [可用性](intro.xhtml#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()`](#os.startfile "os.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()`](os.path.xhtml#os.path.normpath "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`](exceptions.xhtml#NotImplementedError "NotImplementedError") will be raised. [可用性](intro.xhtml#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`](sys.xhtml#sys.stdin "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()`](#os.wait "os.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`](subprocess.xhtml#module-subprocess "subprocess: Subprocess management.") 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](subprocess.xhtml#subprocess-replacements) section in the [`subprocess`](subprocess.xhtml#module-subprocess "subprocess: Subprocess management.") documentation for some helpful recipes. [可用性](intro.xhtml#availability): Unix, Windows。 `os.``times`()Returns the current global process times. The return value is an object with five attributes: - `user` - user time - [`system`](#os.system "os.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`](#os.system "os.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`](#os.system "os.system") are known; the other attributes are zero. [可用性](intro.xhtml#availability): Unix, Windows。在 3.3 版更改: 返回結果的類型由元組變成一個類似元組的對象，同時具有命名的屬性。 `os.``wait`()Wait for completion of a child process, and return a tuple containing its pid and exit status indication: a 16-bit number, whose low byte is the signal number that killed the process, and whose high byte is the exit status (if the signal number is zero); the high bit of the low byte is set if a core file was produced. [可用性](intro.xhtml#availability): Unix。 `os.``waitid`(*idtype*, *id*, *options*)Wait for the completion of one or more child processes. *idtype* can be [`P_PID`](#os.P_PID "os.P_PID"), [`P_PGID`](#os.P_PGID "os.P_PGID") or [`P_ALL`](#os.P_ALL "os.P_ALL"). *id* specifies the pid to wait on. *options* is constructed from the ORing of one or more of [`WEXITED`](#os.WEXITED "os.WEXITED"), [`WSTOPPED`](#os.WSTOPPED "os.WSTOPPED") or [`WCONTINUED`](#os.WCONTINUED "os.WCONTINUED") and additionally may be ORed with [`WNOHANG`](#os.WNOHANG "os.WNOHANG") or [`WNOWAIT`](#os.WNOWAIT "os.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`](#os.WNOHANG "os.WNOHANG") is specified and there are no children in a waitable state. [可用性](intro.xhtml#availability): Unix。 3\.3 新版功能. `os.``P_PID``os.``P_PGID``os.``P_ALL`These are the possible values for *idtype* in [`waitid()`](#os.waitid "os.waitid"). They affect how *id* is interpreted. [可用性](intro.xhtml#availability): Unix。 3\.3 新版功能. `os.``WEXITED``os.``WSTOPPED``os.``WNOWAIT`Flags that can be used in *options* in [`waitid()`](#os.waitid "os.waitid") that specify what child signal to wait for. [可用性](intro.xhtml#availability): Unix。 3\.3 新版功能. `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()`](#os.waitid "os.waitid"). [可用性](intro.xhtml#availability): Unix。 3\.3 新版功能. `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()`](#os.wait "os.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()`](#os.waitpid "os.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`](exceptions.xhtml#OSError "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*`](#os.spawnl "os.spawnl")functions called with [`P_NOWAIT`](#os.P_NOWAIT "os.P_NOWAIT") return suitable process handles. 在 3.5 版更改: 如果系統調用被中斷，但信號處理程序沒有觸發異常，此函數現在會重試系統調用，而不是觸發 [`InterruptedError`](exceptions.xhtml#InterruptedError "InterruptedError") 異常 (原因詳見 [**PEP 475**](https://www.python.org/dev/peps/pep-0475) \[https://www.python.org/dev/peps/pep-0475\])。 `os.``wait3`(*options*)Similar to [`waitpid()`](#os.waitpid "os.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`](resource.xhtml#module-resource "resource: An interface to provide resource usage information on the current process. (Unix)").[`getrusage()`](resource.xhtml#resource.getrusage "resource.getrusage") for details on resource usage information. The option argument is the same as that provided to [`waitpid()`](#os.waitpid "os.waitpid") and [`wait4()`](#os.wait4 "os.wait4"). [可用性](intro.xhtml#availability): Unix。 `os.``wait4`(*pid*, *options*)Similar to [`waitpid()`](#os.waitpid "os.waitpid"), except a 3-element tuple, containing the child's process id, exit status indication, and resource usage information is returned. Refer to [`resource`](resource.xhtml#module-resource "resource: An interface to provide resource usage information on the current process. (Unix)").[`getrusage()`](resource.xhtml#resource.getrusage "resource.getrusage") for details on resource usage information. The arguments to [`wait4()`](#os.wait4 "os.wait4") are the same as those provided to [`waitpid()`](#os.waitpid "os.waitpid"). [可用性](intro.xhtml#availability): Unix。 `os.``WNOHANG`The option for [`waitpid()`](#os.waitpid "os.waitpid") to return immediately if no child process status is available immediately. The function returns `(0, 0)` in this case. [可用性](intro.xhtml#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. [可用性](intro.xhtml#availability): 部分 Unix 系統。 `os.``WUNTRACED`This option causes child processes to be reported if they have been stopped but their current state has not been reported since they were stopped. [可用性](intro.xhtml#availability): Unix。 The following functions take a process status code as returned by [`system()`](#os.system "os.system"), [`wait()`](#os.wait "os.wait"), or [`waitpid()`](#os.waitpid "os.waitpid") as a parameter. They may be used to determine the disposition of a process. `os.``WCOREDUMP`(*status*)Return `True` if a core dump was generated for the process, otherwise return `False`. [可用性](intro.xhtml#availability): Unix。 `os.``WIFCONTINUED`(*status*)Return `True` if the process has been continued from a job control stop, otherwise return `False`. [可用性](intro.xhtml#availability): Unix。 `os.``WIFSTOPPED`(*status*)Return `True` if the process has been stopped, otherwise return `False`. [可用性](intro.xhtml#availability): Unix。 `os.``WIFSIGNALED`(*status*)Return `True` if the process exited due to a signal, otherwise return `False`. [可用性](intro.xhtml#availability): Unix。 `os.``WIFEXITED`(*status*)Return `True` if the process exited using the *exit(2)* system call, otherwise return `False`. [可用性](intro.xhtml#availability): Unix。 `os.``WEXITSTATUS`(*status*)If `WIFEXITED(status)` is true, return the integer parameter to the *exit(2)* system call. Otherwise, the return value is meaningless. [可用性](intro.xhtml#availability): Unix。 `os.``WSTOPSIG`(*status*)Return the signal which caused the process to stop. [可用性](intro.xhtml#availability): Unix。 `os.``WTERMSIG`(*status*)Return the signal which caused the process to exit. [可用性](intro.xhtml#availability): Unix。 ## Interface to the scheduler These functions control how a process is allocated CPU time by the operating system. They are only available on some Unix platforms. For more detailed information, consult your Unix manpages. 3\.3 新版功能. The following scheduling policies are exposed if they are supported by the operating system. `os.``SCHED_OTHER`The default scheduling policy. `os.``SCHED_BATCH`Scheduling policy for CPU-intensive processes that tries to preserve interactivity on the rest of the computer. `os.``SCHED_IDLE`Scheduling policy for extremely low priority background tasks. `os.``SCHED_SPORADIC`Scheduling policy for sporadic server programs. `os.``SCHED_FIFO`A First In First Out scheduling policy. `os.``SCHED_RR`A round-robin scheduling policy. `os.``SCHED_RESET_ON_FORK`This flag can be OR'ed with any other scheduling policy. When a process with this flag set forks, its child's scheduling policy and priority are reset to the default. *class* `os.``sched_param`(*sched\_priority*)This class represents tunable scheduling parameters used in [`sched_setparam()`](#os.sched_setparam "os.sched_setparam"), [`sched_setscheduler()`](#os.sched_setscheduler "os.sched_setscheduler"), and [`sched_getparam()`](#os.sched_getparam "os.sched_getparam"). It is immutable. At the moment, there is only one possible parameter: `sched_priority`The scheduling priority for a scheduling policy. `os.``sched_get_priority_min`(*policy*)Get the minimum priority value for *policy*. *policy* is one of the scheduling policy constants above. `os.``sched_get_priority_max`(*policy*)Get the maximum priority value for *policy*. *policy* is one of the scheduling policy constants above. `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`](#os.sched_param "os.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`](#os.sched_param "os.sched_param") instance. `os.``sched_getparam`(*pid*)Return the scheduling parameters as a [`sched_param`](#os.sched_param "os.sched_param") instance for the process with PID *pid*. A *pid* of 0 means the calling process. `os.``sched_rr_get_interval`(*pid*)Return the round-robin quantum in seconds for the process with PID *pid*. A *pid* of 0 means the calling process. `os.``sched_yield`()Voluntarily relinquish the CPU. `os.``sched_setaffinity`(*pid*, *mask*)Restrict the process with PID *pid* (or the current process if zero) to a set of CPUs. *mask* is an iterable of integers representing the set of CPUs to which the process should be restricted. `os.``sched_getaffinity`(*pid*)Return the set of CPUs the process with PID *pid* (or the current process if zero) is restricted to. ## Miscellaneous System Information `os.``confstr`(*name*)Return string-valued system configuration values. *name* specifies the configuration value to retrieve; it may be a string which is the name of a defined system value; these names are specified in a number of standards (POSIX, Unix 95, Unix 98, and others). Some platforms define additional names as well. The names known to the host operating system are given as the keys of the `confstr_names` dictionary. For configuration variables not included in that mapping, passing an integer for *name* is also accepted. If the configuration value specified by *name* isn't defined, `None` is returned. If *name* is a string and is not known, [`ValueError`](exceptions.xhtml#ValueError "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`](exceptions.xhtml#OSError "OSError") is raised with [`errno.EINVAL`](errno.xhtml#errno.EINVAL "errno.EINVAL") for the error number. [可用性](intro.xhtml#availability): Unix。 `os.``confstr_names`Dictionary mapping names accepted by [`confstr()`](#os.confstr "os.confstr") to the integer values defined for those names by the host operating system. This can be used to determine the set of names known to the system. [可用性](intro.xhtml#availability): Unix。 `os.``cpu_count`()Return the number of CPUs in the system. Returns `None` if undetermined. 該數量不同于當前進程可以使用的CPU數量。可用的CPU數量可以由 `len(os.sched_getaffinity(0))` 方法獲得。 3\.4 新版功能. `os.``getloadavg`()Return the number of processes in the system run queue averaged over the last 1, 5, and 15 minutes or raises [`OSError`](exceptions.xhtml#OSError "OSError") if the load average was unobtainable. [可用性](intro.xhtml#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()`](#os.confstr "os.confstr") apply here as well; the dictionary that provides information on the known names is given by `sysconf_names`. [可用性](intro.xhtml#availability): Unix。 `os.``sysconf_names`Dictionary mapping names accepted by [`sysconf()`](#os.sysconf "os.sysconf") to the integer values defined for those names by the host operating system. This can be used to determine the set of names known to the system. [可用性](intro.xhtml#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`](os.path.xhtml#module-os.path "os.path: Operations on pathnames.") 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.path.xhtml#module-os.path "os.path: Operations on pathnames."). `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.path.xhtml#module-os.path "os.path: Operations on pathnames."). `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()`](os.path.xhtml#os.path.split "os.path.split") and [`os.path.join()`](os.path.xhtml#os.path.join "os.path.join") --- but it is occasionally useful. Also available via [`os.path`](os.path.xhtml#module-os.path "os.path: Operations on pathnames."). `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.path.xhtml#module-os.path "os.path: Operations on pathnames."). `os.``extsep`The character which separates the base filename from the extension; for example, the `'.'` in `os.py`. Also available via [`os.path`](os.path.xhtml#module-os.path "os.path: Operations on pathnames."). `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.path.xhtml#module-os.path "os.path: Operations on pathnames."). `os.``defpath`The default search path used by [`exec*p*`](#os.execl "os.execl") and [`spawn*p*`](#os.spawnl "os.spawnl") if the environment doesn't have a `'PATH'`key. Also available via [`os.path`](os.path.xhtml#module-os.path "os.path: Operations on pathnames."). `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.path.xhtml#module-os.path "os.path: Operations on pathnames."). `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()`](sys.xhtml#sys.setdlopenflags "sys.setdlopenflags") and [`getdlopenflags()`](sys.xhtml#sys.getdlopenflags "sys.getdlopenflags") functions. See the Unix manual page *dlopen(3)* for what the different flags mean. 3\.3 新版功能. ## 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`](#os.GRND_RANDOM "os.GRND_RANDOM") and [`GRND_NONBLOCK`](#os.GRND_NONBLOCK "os.GRND_NONBLOCK"). See also the [Linux getrandom() manual page](http://man7.org/linux/man-pages/man2/getrandom.2.html) \[http://man7.org/linux/man-pages/man2/getrandom.2.html\]. [Availability](intro.xhtml#availability): Linux 3.17 and newer. 3\.6 新版功能. `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**](https://www.python.org/dev/peps/pep-0524) \[https://www.python.org/dev/peps/pep-0524\] for the rationale. On Linux, the [`getrandom()`](#os.getrandom "os.getrandom") function can be used to get random bytes in non-blocking mode (using the [`GRND_NONBLOCK`](#os.GRND_NONBLOCK "os.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`](exceptions.xhtml#NotImplementedError "NotImplementedError") exception is raised. On Windows, it will use `CryptGenRandom()`. 參見 The [`secrets`](secrets.xhtml#module-secrets "secrets: Generate secure random numbers for managing 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`](random.xhtml#random.SystemRandom "random.SystemRandom"). 在 3.6.0 版更改: On Linux, `getrandom()` is now used in blocking mode to increase the security. 在 3.5.2 版更改: On Linux, if the `getrandom()` syscall blocks (the urandom entropy pool is not initialized yet), fall back on reading `/dev/urandom`. 在 3.5 版更改: 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()`](#os.getrandom "os.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`](#os.GRND_NONBLOCK "os.GRND_NONBLOCK") flag is set, then [`getrandom()`](#os.getrandom "os.getrandom") does not block in these cases, but instead immediately raises [`BlockingIOError`](exceptions.xhtml#BlockingIOError "BlockingIOError"). 3\.6 新版功能. `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 新版功能. ### 導航 - [索引](../genindex.xhtml "總目錄") - [模塊](../py-modindex.xhtml "Python 模塊索引") | - [下一頁](io.xhtml "io --- 處理流的核心工具") | - [上一頁](allos.xhtml "通用操作系統服務") | - ![](https://box.kancloud.cn/a721fc7ec672275e257bbbfde49a4d4e_16x16.png) - [Python](https://www.python.org/) ? - zh\_CN 3.7.3 [文檔](../index.xhtml) ? - [Python 標準庫](index.xhtml) ? - [通用操作系統服務](allos.xhtml) ? - $('.inline-search').show(0); | ? [版權所有](../copyright.xhtml) 2001-2019, Python Software Foundation. Python 軟件基金會是一個非盈利組織。 [請捐助。](https://www.python.org/psf/donations/) 最后更新于 5月 21, 2019. 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