`os` — Miscellaneous operating system interfaces¶

Source code: Lib/os.py

This module provides a portable way of using operating system dependent functionality. If you just want to read or write a file see open(), if you want to manipulate paths, see the os.path module, and if you want to read all the lines in all the files on the command line see the fileinput module. For creating temporary files and directories see the tempfile module, and for high-level file and directory handling see the shutil module.

Notes on the availability of these functions:

The design of all built-in operating system dependent modules of Python is such that as long as the same functionality is available, it uses the same interface; for example, the function os.stat(path) returns stat information about path in the same format (which happens to have originated with the POSIX interface).
Extensions peculiar to a particular operating system are also available through the os module, but using them is of course a threat to portability.
All functions accepting path or file names accept both bytes and string objects, and result in an object of the same type, if a path or file name is returned.
On VxWorks, os.popen, os.fork, os.execv and os.spawn*p* are not supported.
On WebAssembly platforms, Android and iOS, large parts of the os module are not available or behave differently. APIs related to processes (e.g. fork(), execve()) and resources (e.g. nice()) are not available. Others like getuid() and getpid() are emulated or stubs. WebAssembly platforms also lack support for signals (e.g. kill(), wait()).

Note

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

exception os.error¶: An alias for the built-in OSError exception.

os.name¶: The name of the operating system dependent module imported. The following names have currently been registered: 'posix', 'nt', 'java'.

See also

sys.platform has a finer granularity. os.uname() gives system-dependent version information.

The platform module provides detailed checks for the system’s identity.

File Names, Command Line Arguments, and Environment Variables¶

In Python, file names, command line arguments, and environment variables are represented using the string type. On some systems, decoding these strings to and from bytes is necessary before passing them to the operating system. Python uses the filesystem encoding and error handler to perform this conversion (see sys.getfilesystemencoding()).

The filesystem encoding and error handler are configured at Python startup by the PyConfig_Read() function: see filesystem_encoding and filesystem_errors members of PyConfig.

Changed in version 3.1: On some systems, conversion using the file system encoding may fail. In this case, Python uses the surrogateescape encoding error handler, which means that undecodable bytes are replaced by a Unicode character U+DCxx on decoding, and these are again translated to the original byte on encoding.

The file system encoding must guarantee to successfully decode all bytes below 128. If the file system encoding fails to provide this guarantee, API functions can raise UnicodeError.

Python UTF-8 Mode¶

Added in version 3.7: See PEP 540 for more details.

The Python UTF-8 Mode ignores the locale encoding and forces the usage of the UTF-8 encoding:

Use UTF-8 as the filesystem encoding.
sys.getfilesystemencoding() returns 'utf-8'.
locale.getpreferredencoding() returns 'utf-8' (the do_setlocale argument has no effect).
sys.stdin, sys.stdout, and sys.stderr all use UTF-8 as their text encoding, with the surrogateescape error handler being enabled for sys.stdin and sys.stdout (sys.stderr continues to use backslashreplace as it does in the default locale-aware mode)
On Unix, os.device_encoding() returns 'utf-8' rather than the device encoding.

Note that the standard stream settings in UTF-8 mode can be overridden by PYTHONIOENCODING (just as they can be in the default locale-aware mode).

As a consequence of the changes in those lower level APIs, other higher level APIs also exhibit different default behaviours:

Command line arguments, environment variables and filenames are decoded to text using the UTF-8 encoding.
os.fsdecode() and os.fsencode() use the UTF-8 encoding.
open(), io.open(), and codecs.open() use the UTF-8 encoding by default. However, they still use the strict error handler by default so that attempting to open a binary file in text mode is likely to raise an exception rather than producing nonsense data.

The Python UTF-8 Mode is enabled if the LC_CTYPE locale is C or POSIX at Python startup (see the PyConfig_Read() function).

It can be enabled or disabled using the -X utf8 command line option and the PYTHONUTF8 environment variable.

If the PYTHONUTF8 environment variable is not set at all, then the interpreter defaults to using the current locale settings, unless the current locale is identified as a legacy ASCII-based locale (as described for PYTHONCOERCECLOCALE), and locale coercion is either disabled or fails. In such legacy locales, the interpreter will default to enabling UTF-8 mode unless explicitly instructed not to do so.

The Python UTF-8 Mode can only be enabled at the Python startup. Its value can be read from sys.flags.utf8_mode.

Process Parameters¶

These functions and data items provide information and operate on the current process and user.

os.ctermid()¶: Return the filename corresponding to the controlling terminal of the process.

Availability: Unix, not WASI.

os.environ¶

A mapping object where keys and values are strings that represent the process environment. For example, environ['HOME'] is the pathname of your home directory (on some platforms), and is equivalent to getenv("HOME") in C.

This mapping is captured the first time the os module is imported, typically during Python startup as part of processing site.py. Changes to the environment made after this time are not reflected in os.environ, except for changes made by modifying os.environ directly.

This mapping may be used to modify the environment as well as query the environment. putenv() will be called automatically when the mapping is modified.

On Unix, keys and values use sys.getfilesystemencoding() and 'surrogateescape' error handler. Use environb if you would like to use a different encoding.

On Windows, the keys are converted to uppercase. This also applies when getting, setting, or deleting an item. For example, environ['monty'] = 'python' maps the key 'MONTY' to the value 'python'.

Note

Calling putenv() directly does not change os.environ, so it’s better to modify os.environ.

Note

On some platforms, including FreeBSD and macOS, setting environ may cause memory leaks. Refer to the system documentation for putenv().

You can delete items in this mapping to unset environment variables. unsetenv() will be called automatically when an item is deleted from os.environ, and when one of the pop() or clear() methods is called.

Changed in version 3.9: Updated to support PEP 584’s merge (|) and update (|=) operators.

os.environb¶

Bytes version of environ: a mapping object where both keys and values are bytes objects representing the process environment. environ and environb are synchronized (modifying environb updates environ, and vice versa).

environb is only available if supports_bytes_environ is True.

Added in version 3.2.

Changed in version 3.9: Updated to support PEP 584’s merge (|) and update (|=) operators.

os.chdir(path)
os.fchdir(fd)
os.getcwd(): These functions are described in Files and Directories.

os.fsencode(filename)¶

Encode path-like filename to the filesystem encoding and error handler; return bytes unchanged.

fsdecode() is the reverse function.

Added in version 3.2.

Changed in version 3.6: Support added to accept objects implementing the os.PathLike interface.

os.fsdecode(filename)¶

Decode the path-like filename from the filesystem encoding and error handler; return str unchanged.

fsencode() is the reverse function.

Added in version 3.2.

Changed in version 3.6: Support added to accept objects implementing the os.PathLike interface.

os.fspath(path)¶

Return the file system representation of the path.

If str or bytes is passed in, it is returned unchanged. Otherwise __fspath__() is called and its value is returned as long as it is a str or bytes object. In all other cases, TypeError is raised.

Added in version 3.6.

class os.PathLike¶

An abstract base class for objects representing a file system path, e.g. pathlib.PurePath.

Added in version 3.6.

abstractmethod __fspath__()¶

Return the file system path representation of the object.

The method should only return a str or bytes object, with the preference being for str.

os.getenv(key, default=None)¶

Return the value of the environment variable key as a string if it exists, or default if it doesn’t. key is a string. Note that since getenv() uses os.environ, the mapping of getenv() is similarly also captured on import, and the function may not reflect future environment changes.

On Unix, keys and values are decoded with sys.getfilesystemencoding() and 'surrogateescape' error handler. Use os.getenvb() if you would like to use a different encoding.

Availability: Unix, Windows.

os.getenvb(key, default=None)¶

Return the value of the environment variable key as bytes if it exists, or default if it doesn’t. key must be bytes. Note that since getenvb() uses os.environb, the mapping of getenvb() is similarly also captured on import, and the function may not reflect future environment changes.

getenvb() is only available if supports_bytes_environ is True.

Availability: Unix.

Added in version 3.2.

os.get_exec_path(env=None)¶: Returns the list of directories that will be searched for a named executable, similar to a shell, when launching a process. env, when specified, should be an environment variable dictionary to lookup the PATH in. By default, when env is None, environ is used.

Added in version 3.2.

os.getegid()¶: Return the effective group id of the current process. This corresponds to the “set id” bit on the file being executed in the current process.

Availability: Unix, not WASI.

os.geteuid()¶: Return the current process’s effective user id.

Availability: Unix, not WASI.

os.getgid()¶: Return the real group id of the current process.

Availability: Unix.

The function is a stub on WASI, see WebAssembly platforms for more information.

os.getgrouplist(user, group, /)¶: Return list of group ids that user belongs to. If group is not in the list, it is included; typically, group is specified as the group ID field from the password record for user, because that group ID will otherwise be potentially omitted.

Availability: Unix, not WASI.

Added in version 3.3.

os.getgroups()¶: Return list of supplemental group ids associated with the current process.

Availability: Unix, not WASI.

Note

On macOS, getgroups() behavior differs somewhat from other Unix platforms. If the Python interpreter was built with a deployment target of 10.5 or earlier, getgroups() returns the list of effective group ids associated with the current user process; this list is limited to a system-defined number of entries, typically 16, and may be modified by calls to setgroups() if suitably privileged. If built with a deployment target greater than 10.5, getgroups() returns the current group access list for the user associated with the effective user id of the process; the group access list may change over the lifetime of the process, it is not affected by calls to setgroups(), and its length is not limited to 16. The deployment target value, MACOSX_DEPLOYMENT_TARGET, can be obtained with sysconfig.get_config_var().

os.getlogin()¶: Return the name of the user logged in on the controlling terminal of the process. For most purposes, it is more useful to use getpass.getuser() since the latter checks the environment variables LOGNAME or USERNAME to find out who the user is, and falls back to pwd.getpwuid(os.getuid())[0] to get the login name of the current real user id.

Availability: Unix, Windows, not WASI.

os.getpgid(pid)¶: Return the process group id of the process with process id pid. If pid is 0, the process group id of the current process is returned.

Availability: Unix, not WASI.

os.getpgrp()¶: Return the id of the current process group.

Availability: Unix, not WASI.

os.getpid()¶

Return the current process id.

The function is a stub on WASI, see WebAssembly platforms for more information.

os.getppid()¶: Return the parent’s process id. When the parent process has exited, on Unix the id returned is the one of the init process (1), on Windows it is still the same id, which may be already reused by another process.

Availability: Unix, Windows, not WASI.

Changed in version 3.2: Added support for Windows.

os.getpriority(which, who)¶: Get program scheduling priority. The value which is one of PRIO_PROCESS, PRIO_PGRP, or PRIO_USER, and who is interpreted relative to which (a process identifier for PRIO_PROCESS, process group identifier for PRIO_PGRP, and a user ID for PRIO_USER). A zero value for who denotes (respectively) the calling process, the process group of the calling process, or the real user ID of the calling process.

Availability: Unix, not WASI.

Added in version 3.3.

os.PRIO_PROCESS¶
os.PRIO_PGRP¶
os.PRIO_USER¶: Parameters for the getpriority() and setpriority() functions.

Availability: Unix, not WASI.

Added in version 3.3.

os.PRIO_DARWIN_THREAD¶
os.PRIO_DARWIN_PROCESS¶
os.PRIO_DARWIN_BG¶
os.PRIO_DARWIN_NONUI¶: Parameters for the getpriority() and setpriority() functions.

Availability: macOS

Added in version 3.12.

os.getresuid()¶: Return a tuple (ruid, euid, suid) denoting the current process’s real, effective, and saved user ids.

Availability: Unix, not WASI.

Added in version 3.2.

os.getresgid()¶: Return a tuple (rgid, egid, sgid) denoting the current process’s real, effective, and saved group ids.

Availability: Unix, not WASI.

Added in version 3.2.

os.getuid()¶: Return the current process’s real user id.

Availability: Unix.

The function is a stub on WASI, see WebAssembly platforms for more information.

os.initgroups(username, gid, /)¶: Call the system initgroups() to initialize the group access list with all of the groups of which the specified username is a member, plus the specified group id.

Availability: Unix, not WASI, not Android.

Added in version 3.2.

os.putenv(key, value, /)¶

Set the environment variable named key to the string value. Such changes to the environment affect subprocesses started with os.system(), popen() or fork() and execv().

Assignments to items in os.environ are automatically translated into corresponding calls to putenv(); however, calls to putenv() don’t update os.environ, so it is actually preferable to assign to items of os.environ. This also applies to getenv() and getenvb(), which respectively use os.environ and os.environb in their implementations.

Note

On some platforms, including FreeBSD and macOS, setting environ may cause memory leaks. Refer to the system documentation for putenv().

Raises an auditing event os.putenv with arguments key, value.

Changed in version 3.9: The function is now always available.

os.setegid(egid, /)¶: Set the current process’s effective group id.

Availability: Unix, not WASI, not Android.

os.seteuid(euid, /)¶: Set the current process’s effective user id.

Availability: Unix, not WASI, not Android.

os.setgid(gid, /)¶: Set the current process’ group id.

Availability: Unix, not WASI, not Android.

os.setgroups(groups, /)¶: Set the list of supplemental group ids associated with the current process to groups. groups must be a sequence, and each element must be an integer identifying a group. This operation is typically available only to the superuser.

Availability: Unix, not WASI.

Note

On macOS, the length of groups may not exceed the system-defined maximum number of effective group ids, typically 16. See the documentation for getgroups() for cases where it may not return the same group list set by calling setgroups().

os.setns(fd, nstype=0)¶

Reassociate the current thread with a Linux namespace. See the setns(2) and namespaces(7) man pages for more details.

If fd refers to a /proc/pid/ns/ link, setns() reassociates the calling thread with the namespace associated with that link, and nstype may be set to one of the CLONE_NEW* constants to impose constraints on the operation (0 means no constraints).

Since Linux 5.8, fd may refer to a PID file descriptor obtained from pidfd_open(). In this case, setns() reassociates the calling thread into one or more of the same namespaces as the thread referred to by fd. This is subject to any constraints imposed by nstype, which is a bit mask combining one or more of the CLONE_NEW* constants, e.g. setns(fd, os.CLONE_NEWUTS | os.CLONE_NEWPID). The caller’s memberships in unspecified namespaces are left unchanged.

fd can be any object with a fileno() method, or a raw file descriptor.

This example reassociates the thread with the init process’s network namespace:

fd = os.open("/proc/1/ns/net", os.O_RDONLY)
os.setns(fd, os.CLONE_NEWNET)
os.close(fd)

Availability: Linux >= 3.0 with glibc >= 2.14.

Added in version 3.12.

File Object Creation¶

These functions create new file objects. (See also open() for opening file descriptors.)

os.fdopen(fd, *args, **kwargs)¶: Return an open file object connected to the file descriptor fd. This is an alias of the open() built-in function and accepts the same arguments. The only difference is that the first argument of fdopen() must always be an integer.

File Descriptor Operations¶

These functions operate on I/O streams referenced using file descriptors.

File descriptors are small integers corresponding to a file that has been opened by the current process. For example, standard input is usually file descriptor 0, standard output is 1, and standard error is 2. Further files opened by a process will then be assigned 3, 4, 5, and so forth. The name “file descriptor” is slightly deceptive; on Unix platforms, sockets and pipes are also referenced by file descriptors.

The fileno() method can be used to obtain the file descriptor associated with a file object when required. Note that using the file descriptor directly will bypass the file object methods, ignoring aspects such as internal buffering of data.

os.close(fd)¶: Close file descriptor fd.

Note

This function is intended for low-level I/O and must be applied to a file descriptor as returned by os.open() or pipe(). To close a “file object” returned by the built-in function open() or by popen() or fdopen(), use its close() method.

os.closerange(fd_low, fd_high, /)¶

Close all file descriptors from fd_low (inclusive) to fd_high (exclusive), ignoring errors. Equivalent to (but much faster than):

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

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

Copy count bytes from file descriptor src, starting from offset offset_src, to file descriptor dst, starting from offset offset_dst. If offset_src is None, then src is read from the current position; respectively for offset_dst.

In Linux kernel older than 5.3, the files pointed to by src and dst must reside in the same filesystem, otherwise an OSError is raised with errno set to errno.EXDEV.

This copy is done without the additional cost of transferring data from the kernel to user space and then back into the kernel. Additionally, some filesystems could implement extra optimizations, such as the use of reflinks (i.e., two or more inodes that share pointers to the same copy-on-write disk blocks; supported file systems include btrfs and XFS) and server-side copy (in the case of NFS).

The function copies bytes between two file descriptors. Text options, like the encoding and the line ending, are ignored.

The return value is the amount of bytes copied. This could be less than the amount requested.

Note

On Linux, os.copy_file_range() should not be used for copying a range of a pseudo file from a special filesystem like procfs and sysfs. It will always copy no bytes and return 0 as if the file was empty because of a known Linux kernel issue.

Availability: Linux >= 4.5 with glibc >= 2.27.

Added in version 3.8.

os.device_encoding(fd)¶

Return a string describing the encoding of the device associated with fd if it is connected to a terminal; else return None.

On Unix, if the Python UTF-8 Mode is enabled, return 'UTF-8' rather than the device encoding.

Changed in version 3.10: On Unix, the function now implements the Python UTF-8 Mode.

os.dup(fd, /)¶

Return a duplicate of file descriptor fd. The new file descriptor is non-inheritable.

On Windows, when duplicating a standard stream (0: stdin, 1: stdout, 2: stderr), the new file descriptor is inheritable.

Availability: not WASI.

Changed in version 3.4: The new file descriptor is now non-inheritable.

os.dup2(fd, fd2, inheritable=True)¶: Duplicate file descriptor fd to fd2, closing the latter first if necessary. Return fd2. The new file descriptor is inheritable by default or non-inheritable if inheritable is False.

Availability: not WASI.

Changed in version 3.4: Add the optional inheritable parameter.

Changed in version 3.7: Return fd2 on success. Previously, None was always returned.

os.fchmod(fd, mode)¶

Change the mode of the file given by fd to the numeric mode. See the docs for chmod() for possible values of mode. As of Python 3.3, this is equivalent to os.chmod(fd, mode).

Raises an auditing event os.chmod with arguments path, mode, dir_fd.

Availability: Unix, Windows.

The function is limited on WASI, see WebAssembly platforms for more information.

Changed in version 3.13: Added support on Windows.

os.fchown(fd, uid, gid)¶

Change the owner and group id of the file given by fd to the numeric uid and gid. To leave one of the ids unchanged, set it to -1. See chown(). As of Python 3.3, this is equivalent to os.chown(fd, uid, gid).

Raises an auditing event os.chown with arguments path, uid, gid, dir_fd.

Availability: Unix.

The function is limited on WASI, see WebAssembly platforms for more information.

os.fdatasync(fd)¶: Force write of file with filedescriptor fd to disk. Does not force update of metadata.

Availability: Unix.

Note

This function is not available on MacOS.

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 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 is raised with errno.EINVAL for the error number.

As of Python 3.3, this is equivalent to os.pathconf(fd, name).

Availability: Unix.

os.fstat(fd)¶

Get the status of the file descriptor fd. Return a stat_result object.

As of Python 3.3, this is equivalent to os.stat(fd).

See also

The stat() function.

os.fstatvfs(fd, /)¶: Return information about the filesystem containing the file associated with file descriptor fd, like statvfs(). As of Python 3.3, this is equivalent to os.statvfs(fd).

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 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.

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).

Raises an auditing event os.truncate with arguments fd, length.

Availability: Unix, Windows.

Changed in version 3.5: Added support for Windows

os.get_blocking(fd, /)¶

Get the blocking mode of the file descriptor: False if the O_NONBLOCK flag is set, True if the flag is cleared.

Availability: Unix, Windows.

The function is limited on WASI, see WebAssembly platforms for more information.

On Windows, this function is limited to pipes.

Added in version 3.5.

Changed in version 3.12: Added support for pipes on Windows.

os.grantpt(fd, /)¶

Grant access to the slave pseudo-terminal device associated with the master pseudo-terminal device to which the file descriptor fd refers. The file descriptor fd is not closed upon failure.

Calls the C standard library function grantpt().

Availability: Unix, not WASI.

Added in version 3.13.

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, F_TLOCK, F_ULOCK or F_TEST. len specifies the section of the file to lock.

Raises an auditing event os.lockf with arguments fd, cmd, len.

Availability: Unix.

Added in version 3.3.

os.F_LOCK¶
os.F_TLOCK¶
os.F_ULOCK¶
os.F_TEST¶: Flags that specify what action lockf() will take.

Availability: Unix.

Added in version 3.3.

os.login_tty(fd, /)¶: Prepare the tty of which fd is a file descriptor for a new login session. Make the calling process a session leader; make the tty the controlling tty, the stdin, the stdout, and the stderr of the calling process; close fd.

Availability: Unix, not WASI.

Added in version 3.11.

os.lseek(fd, pos, whence, /)¶

Set the current position of file descriptor fd to position pos, modified by whence, and return the new position in bytes relative to the start of the file. Valid values for whence are:

SEEK_SET or 0 – set pos relative to the beginning of the file
SEEK_CUR or 1 – set pos relative to the current file position
SEEK_END or 2 – set pos relative to the end of the file
SEEK_HOLE – set pos to the next data location, relative to pos
SEEK_DATA – set pos to the next data hole, relative to pos

Changed in version 3.3: Add support for SEEK_HOLE and SEEK_DATA.

os.SEEK_SET¶

os.SEEK_CUR¶

os.SEEK_END¶

Parameters to the lseek() function and the seek() method on file-like objects, for whence to adjust the file position indicator.

SEEK_SET: Adjust the file position relative to the beginning of the file.
SEEK_CUR: Adjust the file position relative to the current file position.
SEEK_END: Adjust the file position relative to the end of the file.

Their values are 0, 1, and 2, respectively.

os.SEEK_HOLE¶

os.SEEK_DATA¶

Parameters to the lseek() function and the seek() method on file-like objects, for seeking file data and holes on sparsely allocated files.

SEEK_DATA: Adjust the file offset to the next location containing data, relative to the seek position.
SEEK_HOLE: Adjust the file offset to the next location containing a hole, relative to the seek position. A hole is defined as a sequence of zeros.

Note

These operations only make sense for filesystems that support them.

Availability: Linux >= 3.1, macOS, Unix

Added in version 3.3.

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.

For a description of the flag and mode values, see the C run-time documentation; flag constants (like O_RDONLY and O_WRONLY) are defined in the os module. In particular, on Windows adding O_BINARY is needed to open files in binary mode.

This function can support paths relative to directory descriptors with the dir_fd parameter.

Raises an auditing event open with arguments path, mode, flags.

Changed in version 3.4: The new file descriptor is now non-inheritable.

Note

This function is intended for low-level I/O. For normal usage, use the built-in function open(), which returns a file object with read() and write() methods (and many more). To wrap a file descriptor in a file object, use fdopen().

Changed in version 3.3: Added the dir_fd parameter.

Changed in version 3.5: If the system call is interrupted and the signal handler does not raise an exception, the function now retries the system call instead of raising an InterruptedError exception (see PEP 475 for the rationale).

Changed in version 3.6: Accepts a path-like object.

The following constants are options for the flags parameter to the 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 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¶: The above constants are only available on Unix.

Changed in version 3.3: Add 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¶: The above constants are only available on Windows.

os.O_EVTONLY¶
os.O_FSYNC¶
os.O_SYMLINK¶
os.O_NOFOLLOW_ANY¶: The above constants are only available on macOS.

Changed in version 3.10: Add O_EVTONLY, O_FSYNC, O_SYMLINK and O_NOFOLLOW_ANY constants.

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.

Changed in version 3.4: Add O_PATH on systems that support it. Add 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. For a (slightly) more portable approach, use the pty module.

Availability: Unix, not WASI.

Changed in version 3.4: The new file descriptors are now non-inheritable.

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.

Availability: Unix, Windows.

Changed in version 3.4: The new file descriptors are now non-inheritable.

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, O_CLOEXEC. Return a pair of file descriptors (r, w) usable for reading and writing, respectively.

Availability: Unix, not WASI.

Added in version 3.3.

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.

Availability: Unix.

Added in version 3.3.

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, POSIX_FADV_SEQUENTIAL, POSIX_FADV_RANDOM, POSIX_FADV_NOREUSE, POSIX_FADV_WILLNEED or POSIX_FADV_DONTNEED.

Availability: Unix.

Added in version 3.3.

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() that specify the access pattern that is likely to be used.

Availability: Unix.

Added in version 3.3.

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.

Availability: Unix.

Added in version 3.3.

os.posix_openpt(oflag, /)¶

Open and return a file descriptor for a master pseudo-terminal device.

Calls the C standard library function posix_openpt(). The oflag argument is used to set file status flags and file access modes as specified in the manual page of posix_openpt() of your system.

The returned file descriptor is non-inheritable. If the value O_CLOEXEC is available on the system, it is added to oflag.

Availability: Unix, not WASI.

Added in version 3.13.

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

Read from a file descriptor fd at a position of offset into mutable bytes-like objects 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:

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() value 'SC_IOV_MAX') on the number of buffers that can be used.

Combine the functionality of os.readv() and os.pread().

Availability: Linux >= 2.6.30, FreeBSD >= 6.0, OpenBSD >= 2.7, AIX >= 7.1.

Using flags requires Linux >= 4.6.

Added in version 3.7.

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.

Availability: Linux >= 4.14.

Added in version 3.7.

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 flag.

Availability: Linux >= 4.6.

Added in version 3.7.

os.ptsname(fd, /)¶

Return the name of the slave pseudo-terminal device associated with the master pseudo-terminal device to which the file descriptor fd refers. The file descriptor fd is not closed upon failure.

Calls the reentrant C standard library function ptsname_r() if it is available; otherwise, the C standard library function ptsname(), which is not guaranteed to be thread-safe, is called.

Availability: Unix, not WASI.

Added in version 3.13.

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.

Availability: Unix.

Added in version 3.3.

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

Write the buffers contents to file descriptor fd at an offset offset, leaving the file offset unchanged. buffers must be a sequence of bytes-like objects. 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:

Return the total number of bytes actually written.

The operating system may set a limit (sysconf() value 'SC_IOV_MAX') on the number of buffers that can be used.

Combine the functionality of os.writev() and os.pwrite().

Availability: Linux >= 2.6.30, FreeBSD >= 6.0, OpenBSD >= 2.7, AIX >= 7.1.

Using flags requires Linux >= 4.6.

Added in version 3.7.

os.RWF_DSYNC¶: Provide a per-write equivalent of the O_DSYNC os.open() flag. This flag effect applies only to the data range written by the system call.

Availability: Linux >= 4.7.

Added in version 3.7.

os.RWF_SYNC¶: Provide a per-write equivalent of the O_SYNC os.open() flag. This flag effect applies only to the data range written by the system call.

Availability: Linux >= 4.7.

Added in version 3.7.

os.RWF_APPEND¶: Provide a per-write equivalent of the O_APPEND os.open() flag. This flag is meaningful only for os.pwritev(), and its effect applies only to the data range written by the system call. The offset argument does not affect the write operation; the data is always appended to the end of the file. However, if the offset argument is -1, the current file offset is updated.

Availability: Linux >= 4.16.

Added in version 3.10.

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.

Note

This function is intended for low-level I/O and must be applied to a file descriptor as returned by os.open() or pipe(). To read a “file object” returned by the built-in function open() or by popen() or fdopen(), or sys.stdin, use its read() or readline() methods.

os.sendfile(out_fd, in_fd, offset, count)¶

os.sendfile(out_fd, in_fd, offset, count, headers=(), trailers=(), flags=0)

Copy count bytes from file descriptor in_fd to file descriptor out_fd 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().

On Linux, if offset is given as None, the bytes are read from the current position of in_fd and the position of in_fd is updated.

The second case may be used on macOS and FreeBSD where headers and trailers are arbitrary sequences of buffers that are written before and after the data from in_fd is written. It returns the same as the first case.

On macOS and FreeBSD, a value of 0 for count specifies to send until the end of in_fd is reached.

All platforms support sockets as out_fd 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.

Availability: Unix, not WASI.

Note

For a higher-level wrapper of sendfile(), see socket.socket.sendfile().

Added in version 3.3.

Changed in version 3.9: Parameters out and in was renamed to out_fd and in_fd.

os.SF_NODISKIO¶
os.SF_MNOWAIT¶
os.SF_SYNC¶: Parameters to the sendfile() function, if the implementation supports them.

Availability: Unix, not WASI.

Added in version 3.3.

os.SF_NOCACHE¶: Parameter to the sendfile() function, if the implementation supports it. The data won’t be cached in the virtual memory and will be freed afterwards.

Availability: Unix, not WASI.

Added in version 3.11.

os.set_blocking(fd, blocking, /)¶

Set the blocking mode of the specified file descriptor. Set the O_NONBLOCK flag if blocking is False, clear the flag otherwise.

Availability: Unix, Windows.

The function is limited on WASI, see WebAssembly platforms for more information.

On Windows, this function is limited to pipes.

Added in version 3.5.

Changed in version 3.12: Added support for pipes on Windows.

os.splice(src, dst, count, offset_src=None, offset_dst=None)¶

Transfer count bytes from file descriptor src, starting from offset offset_src, to file descriptor dst, starting from offset offset_dst. At least one of the file descriptors must refer to a pipe. If offset_src is None, then src is read from the current position; respectively for offset_dst. The offset associated to the file descriptor that refers to a pipe must be None. The files pointed to by src and dst must reside in the same filesystem, otherwise an OSError is raised with errno set to errno.EXDEV.

Upon successful completion, returns the number of bytes spliced to or from the pipe. A return value of 0 means end of input. If src refers to a pipe, then this means that there was no data to transfer, and it would not make sense to block because there are no writers connected to the write end of the pipe.

Availability: Linux >= 2.6.17 with glibc >= 2.5

Added in version 3.10.

os.SPLICE_F_MOVE¶
os.SPLICE_F_NONBLOCK¶
os.SPLICE_F_MORE¶: Added in version 3.10.

os.readv(fd, buffers, /)¶

Read from a file descriptor fd into a number of mutable bytes-like objects 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() value 'SC_IOV_MAX') on the number of buffers that can be used.

Availability: Unix.

Added in version 3.3.

os.tcgetpgrp(fd, /)¶: Return the process group associated with the terminal given by fd (an open file descriptor as returned by os.open()).

Availability: Unix, not WASI.

os.tcsetpgrp(fd, pg, /)¶: Set the process group associated with the terminal given by fd (an open file descriptor as returned by os.open()) to pg.

Availability: Unix, not WASI.

os.ttyname(fd, /)

os — Miscellaneous operating system interfaces¶

File Names, Command Line Arguments, and Environment Variables¶

Python UTF-8 Mode¶

Process Parameters¶

File Object Creation¶

File Descriptor Operations¶

`os` — Miscellaneous operating system interfaces¶