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.
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.
-
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 file system encoding to perform this conversion (see
sys.getfilesystemencoding()
).
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 may raise UnicodeErrors.
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.
-
os.
environ
¶ A mapping object representing the string environment. For example,
environ['HOME']
is the pathname of your home directory (on some platforms), and is equivalent togetenv("HOME")
in C.This mapping is captured the first time the
os
module is imported, typically during Python startup as part of processingsite.py
. Changes to the environment made after this time are not reflected inos.environ
, except for changes made by modifyingos.environ
directly.If the platform supports the
putenv()
function, 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. Useenvironb
if you would like to use a different encoding.Note
Calling
putenv()
directly does not changeos.environ
, so it’s better to modifyos.environ
.Note
On some platforms, including FreeBSD and Mac OS X, setting
environ
may cause memory leaks. Refer to the system documentation forputenv()
.If
putenv()
is not provided, a modified copy of this mapping may be passed to the appropriate process-creation functions to cause child processes to use a modified environment.If the platform supports the
unsetenv()
function, you can delete items in this mapping to unset environment variables.unsetenv()
will be called automatically when an item is deleted fromos.environ
, and when one of thepop()
orclear()
methods is called.
-
os.
environb
¶ Bytes version of
environ
: a mapping object representing the environment as byte strings.environ
andenvironb
are synchronized (modifyenvironb
updatesenviron
, and vice versa).environb
is only available ifsupports_bytes_environ
is True.New in version 3.2.
-
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 with
'surrogateescape'
error handler, or'strict'
on Windows; returnbytes
unchanged.fsdecode()
is the reverse function.New 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 with
'surrogateescape'
error handler, or'strict'
on Windows; returnstr
unchanged.fsencode()
is the reverse function.New 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
orbytes
is passed in, it is returned unchanged. Otherwise__fspath__()
is called and its value is returned as long as it is astr
orbytes
object. In all other cases,TypeError
is raised.New in version 3.6.
-
class
os.
PathLike
¶ An abstract base class for objects representing a file system path, e.g.
pathlib.PurePath
.New in version 3.6.
-
os.
getenv
(key, default=None)¶ Return the value of the environment variable key if it exists, or default if it doesn’t. key, default and the result are str.
On Unix, keys and values are decoded with
sys.getfilesystemencoding()
and'surrogateescape'
error handler. Useos.getenvb()
if you would like to use a different encoding.Availability: most flavors of Unix, Windows.
-
os.
getenvb
(key, default=None)¶ Return the value of the environment variable key if it exists, or default if it doesn’t. key, default and the result are bytes.
getenvb()
is only available ifsupports_bytes_environ
is True.Availability: most flavors of Unix.
New 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.New 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.
-
os.
geteuid
()¶ Return the current process’s effective user id.
Availability: Unix.
-
os.
getgid
()¶ Return the real group id of the current process.
Availability: Unix.
-
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.
Availability: Unix.
New in version 3.3.
-
os.
getgroups
()¶ Return list of supplemental group ids associated with the current process.
Availability: Unix.
Note
On Mac OS X,
getgroups()
behavior differs somewhat from other Unix platforms. If the Python interpreter was built with a deployment target of10.5
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 tosetgroups()
if suitably privileged. If built with a deployment target greater than10.5
,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 tosetgroups()
, and its length is not limited to 16. The deployment target value,MACOSX_DEPLOYMENT_TARGET
, can be obtained withsysconfig.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 variablesLOGNAME
orUSERNAME
to find out who the user is, and falls back topwd.getpwuid(os.getuid())[0]
to get the login name of the current real user id.Availability: Unix, Windows.
-
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.
-
os.
getpgrp
()¶ Return the id of the current process group.
Availability: Unix.
-
os.
getpid
()¶ Return the current process id.
-
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.
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
, orPRIO_USER
, and who is interpreted relative to which (a process identifier forPRIO_PROCESS
, process group identifier forPRIO_PGRP
, and a user ID forPRIO_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.
New in version 3.3.
-
os.
PRIO_PROCESS
¶ -
os.
PRIO_PGRP
¶ -
os.
PRIO_USER
¶ Parameters for the
getpriority()
andsetpriority()
functions.Availability: Unix.
New in version 3.3.
-
os.
getresuid
()¶ Return a tuple (ruid, euid, suid) denoting the current process’s real, effective, and saved user ids.
Availability: Unix.
New 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.
New in version 3.2.
-
os.
getuid
()¶ Return the current process’s real user id.
Availability: Unix.
-
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.
New 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()
orfork()
andexecv()
.Availability: most flavors of Unix, Windows.
Note
On some platforms, including FreeBSD and Mac OS X, setting
environ
may cause memory leaks. Refer to the system documentation for putenv.When
putenv()
is supported, assignments to items inos.environ
are automatically translated into corresponding calls toputenv()
; however, calls toputenv()
don’t updateos.environ
, so it is actually preferable to assign to items ofos.environ
.
-
os.
setegid
(egid)¶ Set the current process’s effective group id.
Availability: Unix.
-
os.
seteuid
(euid)¶ Set the current process’s effective user id.
Availability: Unix.
-
os.
setgid
(gid)¶ Set the current process’ group id.
Availability: Unix.
-
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.
Note
On Mac OS X, 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.
setpgrp
()¶ Call the system call
setpgrp()
orsetpgrp(0, 0)
depending on which version is implemented (if any). See the Unix manual for the semantics.Availability: Unix.
-
os.
setpgid
(pid, pgrp)¶ Call the system call
setpgid()
to set the process group id of the process with id pid to the process group with id pgrp. See the Unix manual for the semantics.Availability: Unix.
-
os.
setpriority
(which, who, priority)¶ Set program scheduling priority. The value which is one of
PRIO_PROCESS
,PRIO_PGRP
, orPRIO_USER
, and who is interpreted relative to which (a process identifier forPRIO_PROCESS
, process group identifier forPRIO_PGRP
, and a user ID forPRIO_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. priority is a value in the range -20 to 19. The default priority is 0; lower priorities cause more favorable scheduling.Availability: Unix.
New in version 3.3.
-
os.
setregid
(rgid, egid)¶ Set the current process’s real and effective group ids.
Availability: Unix.
-
os.
setresgid
(rgid, egid, sgid)¶ Set the current process’s real, effective, and saved group ids.
Availability: Unix.
New in version 3.2.
-
os.
setresuid
(ruid, euid, suid)¶ Set the current process’s real, effective, and saved user ids.
Availability: Unix.
New in version 3.2.
-
os.
setreuid
(ruid, euid)¶ Set the current process’s real and effective user ids.
Availability: Unix.
-
os.
getsid
(pid)¶ Call the system call
getsid()
. See the Unix manual for the semantics.Availability: Unix.
-
os.
setsid
()¶ Call the system call
setsid()
. See the Unix manual for the semantics.Availability: Unix.
-
os.
setuid
(uid)¶ Set the current process’s user id.
Availability: Unix.
-
os.
strerror
(code)¶ Return the error message corresponding to the error code in code. On platforms where
strerror()
returnsNULL
when given an unknown error number,ValueError
is raised.
-
os.
supports_bytes_environ
¶ True
if the native OS type of the environment is bytes (eg.False
on Windows).New in version 3.2.
-
os.
umask
(mask)¶ Set the current numeric umask and return the previous umask.
-
os.
uname
()¶ Returns information identifying the current operating system. The return value is an object with five attributes:
sysname
- operating system namenodename
- name of machine on network (implementation-defined)release
- operating system releaseversion
- operating system versionmachine
- hardware identifier
For backwards compatibility, this object is also iterable, behaving like a five-tuple containing
sysname
,nodename
,release
,version
, andmachine
in that order.Some systems truncate
nodename
to 8 characters or to the leading component; a better way to get the hostname issocket.gethostname()
or evensocket.gethostbyaddr(socket.gethostname())
.Availability: recent flavors of Unix.
Changed in version 3.3: Return type changed from a tuple to a tuple-like object with named attributes.
-
os.
unsetenv
(key)¶ Unset (delete) the environment variable named key. Such changes to the environment affect subprocesses started with
os.system()
,popen()
orfork()
andexecv()
.When
unsetenv()
is supported, deletion of items inos.environ
is automatically translated into a corresponding call tounsetenv()
; however, calls tounsetenv()
don’t updateos.environ
, so it is actually preferable to delete items ofos.environ
.Availability: most flavors of Unix, Windows.
File Object Creation¶
This function creates new file objects. (See also
open()
for opening file descriptors.)
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.
-
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.
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
.
-
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.
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
.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 toos.chmod(fd, mode)
.Availability: Unix.
-
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 toos.chown(fd, uid, gid)
.Availability: Unix.
-
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 inpathconf_names
, anOSError
is raised witherrno.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 toos.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 doos.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)
.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 theO_NONBLOCK
flag is set,True
if the flag is cleared.See also
set_blocking()
andsocket.socket.setblocking()
.Availability: Unix.
New in version 3.5.
-
os.
isatty
(fd)¶ Return
True
if the file descriptor fd is open and connected to a tty(-like) device, elseFalse
.
-
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
orF_TEST
. len specifies the section of the file to lock.Availability: Unix.
New 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.
New in version 3.3.
-
os.
lseek
(fd, pos, how)¶ Set the current position of file descriptor fd to position pos, modified by how:
SEEK_SET
or0
to set the position relative to the beginning of the file;SEEK_CUR
or1
to set it relative to the current position;SEEK_END
or2
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()
function. Their values are 0, 1, and 2, respectively.New in version 3.3: Some operating systems could support additional values, like
os.SEEK_HOLE
oros.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.
For a description of the flag and mode values, see the C run-time documentation; flag constants (like
O_RDONLY
andO_WRONLY
) are defined in theos
module. In particular, on Windows addingO_BINARY
is needed to open files in binary mode.This function can support paths relative to directory descriptors with the dir_fd parameter.
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 withread()
andwrite()
methods (and many more). To wrap a file descriptor in a file object, usefdopen()
.New in version 3.3: The dir_fd argument.
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_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.
-
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 thepty
module.Availability: some flavors of Unix.
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: some flavors of Unix.
New 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.
New 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
orPOSIX_FADV_DONTNEED
.Availability: Unix.
New 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.
New 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.
New in version 3.3.
-
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()
andos.pread()
.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.
New 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 toerrno.EAGAIN
.Availability: Linux 4.14 and newer.
New 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 and newer.
New in version 3.7.
-
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.
New in version 3.3.
-
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. 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()
andos.pwrite()
.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.
New in version 3.7.
-
os.
RWF_DSYNC
¶ Provide a per-write equivalent of the
O_DSYNC
open(2)
flag. This flag effect applies only to the data range written by the system call.Availability: Linux 4.7 and newer.
New in version 3.7.
-
os.
RWF_SYNC
¶ Provide a per-write equivalent of the
O_SYNC
open(2)
flag. This flag effect applies only to the data range written by the system call.Availability: Linux 4.7 and newer.
New in version 3.7.
-
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()
orpipe()
. To read a “file object” returned by the built-in functionopen()
or bypopen()
orfdopen()
, orsys.stdin
, use itsread()
orreadline()
methods.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).
-
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()
.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.
Availability: Unix.
Note
For a higher-level wrapper of
sendfile()
, seesocket.socket.sendfile()
.New in version 3.3.
-
os.
set_blocking
(fd, blocking)¶ Set the blocking mode of the specified file descriptor. Set the
O_NONBLOCK
flag if blocking isFalse
, clear the flag otherwise.See also
get_blocking()
andsocket.socket.setblocking()
.Availability: Unix.
New in version 3.5.
-
os.
SF_NODISKIO
¶ -
os.
SF_MNOWAIT
¶ -
os.
SF_SYNC
¶ Parameters to the
sendfile()
function, if the implementation supports them.Availability: Unix.
New in version 3.3.
-
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.
New 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.
-
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.
-
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.
Availability: Unix.
-
os.
write
(fd, str)¶ Write the bytestring in str to file descriptor fd.
Return the number of bytes actually written.
Note
This function is intended for low-level I/O and must be applied to a file descriptor as returned by
os.open()
orpipe()
. To write a “file object” returned by the built-in functionopen()
or bypopen()
orfdopen()
, orsys.stdout
orsys.stderr
, use itswrite()
method.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).
-
os.
writev
(fd, buffers)¶ Write the contents of buffers to file descriptor fd. buffers must be a sequence of bytes-like objects. Buffers are processed in array order. Entire contents of 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()
value'SC_IOV_MAX'
) on the number of buffers that can be used.Availability: Unix.
New in version 3.3.
Querying the size of a terminal¶
New in version 3.3.
-
os.
get_terminal_size
(fd=STDOUT_FILENO)¶ Return the size of the terminal window as
(columns, lines)
, tuple of typeterminal_size
.The optional argument
fd
(defaultSTDOUT_FILENO
, or standard output) specifies which file descriptor should be queried.If the file descriptor is not connected to a terminal, an
OSError
is raised.shutil.get_terminal_size()
is the high-level function which should normally be used,os.get_terminal_size
is the low-level implementation.Availability: Unix, Windows.
Inheritance of File Descriptors¶
New in version 3.4.
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*
functions,
all inheritable handles and all inheritable file descriptors are inherited.
Using the subprocess
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).
Availability: Windows.
-
os.
set_handle_inheritable
(handle, inheritable)¶ Set the “inheritable” flag of the specified handle.
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
. If it is unavailable, using it will raise aNotImplementedError
.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
orf...at
version of the function.)You can check whether or not dir_fd is supported on your platform using
os.supports_dir_fd
. If it is unavailable, using it will raise aNotImplementedError
.
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 thel...
version of the function.)You can check whether or not follow_symlinks is supported on your platform using
os.supports_follow_symlinks
. If it is unavailable, using it will raise aNotImplementedError
.
-
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
to test the existence of path, or it can be the inclusive OR of one or more ofR_OK
,W_OK
, andX_OK
to test permissions. ReturnTrue
if access is allowed,False
if not. See the Unix man page access(2) for more information.This function can support specifying paths relative to directory descriptors and not following symlinks.
If effective_ids is
True
,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 usingos.supports_effective_ids
. If it is unavailable, using it will raise aNotImplementedError
.Note
Using
access()
to check if a user is authorized to e.g. open a file before actually doing so usingopen()
creates a security hole, because the user might exploit the short time interval between checking and opening the file to manipulate it. It’s preferable to use EAFP techniques. For example:if os.access("myfile", os.R_OK): with open("myfile") as fp: return fp.read() return "some default data"
is better written as:
try: fp = open("myfile") except PermissionError: return "some default data" else: with fp: return fp.read()
Note
I/O operations may fail even when
access()
indicates that they would succeed, particularly for operations on network filesystems which may have permissions semantics beyond the usual POSIX permission-bit model.Changed in version 3.3: Added the dir_fd, effective_ids, and follow_symlinks parameters.
Changed in version 3.6: Accepts a path-like object.
-
os.
F_OK
¶ -
os.
R_OK
¶ -
os.
W_OK
¶ -
os.
X_OK
¶ Values to pass as the mode parameter of
access()
to test the existence, readability, writability and executability of path, respectively.
-
os.
chdir
(path)¶ Change the current working directory to path.
This function can support specifying a file descriptor. The descriptor must refer to an opened directory, not an open file.
This function can raise
OSError
and subclasses such asFileNotFoundError
,PermissionError
, andNotADirectoryError
.New in version 3.3: Added support for specifying path as a file descriptor on some platforms.
Changed in version 3.6: Accepts a 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
module):This function can support not following symlinks.
Availability: Unix.
New in version 3.3: The follow_symlinks argument.
Changed in version 3.6: Accepts a path-like object.
-
os.
chmod
(path, mode, *, dir_fd=None, follow_symlinks=True)¶ Change the mode of path to the numeric mode. mode may take one of the following values (as defined in the
stat
module) or bitwise ORed combinations of them:This function can support specifying a file descriptor, paths relative to directory descriptors and not following symlinks.
Note
Although Windows supports
chmod()
, you can only set the file’s read-only flag with it (via thestat.S_IWRITE
andstat.S_IREAD
constants or a corresponding integer value). All other bits are ignored.New in version 3.3: Added support for specifying path as an open file descriptor, and the dir_fd and follow_symlinks arguments.
Changed in version 3.6: Accepts a path-like object.
-
os.
chown
(path, uid, gid, *, dir_fd=None, follow_symlinks=True)¶ Change the owner and group id of path to the numeric uid and gid. To leave one of the ids unchanged, set it to -1.
This function can support specifying a file descriptor, paths relative to directory descriptors and not following symlinks.
See
shutil.chown()
for a higher-level function that accepts names in addition to numeric ids.Availability: Unix.
New in version 3.3: Added support for specifying an open file descriptor for path, and the dir_fd and follow_symlinks arguments.
Changed in version 3.6: Supports a path-like object.
-
os.
chroot
(path)¶ Change the root directory of the current process to path.
Availability: Unix.
Changed in version 3.6: Accepts a path-like object.
-
os.
fchdir
(fd)¶ Change the current working directory to the directory represented by the file descriptor fd. The descriptor must refer to an opened directory, not an open file. As of Python 3.3, this is equivalent to
os.chdir(fd)
.Availability: Unix.
-
os.
getcwd
()¶ Return a string representing the current working directory.
-
os.
getcwdb
()¶ Return a bytestring representing the current working directory.
-
os.
lchflags
(path, flags)¶ Set the flags of path to the numeric flags, like
chflags()
, but do not follow symbolic links. As of Python 3.3, this is equivalent toos.chflags(path, flags, follow_symlinks=False)
.Availability: Unix.
Changed in version 3.6: Accepts a path-like object.
-
os.
lchmod
(path, mode)¶ Change the mode of path to the numeric mode. If path is a symlink, this affects the symlink rather than the target. See the docs for
chmod()
for possible values of mode. As of Python 3.3, this is equivalent toos.chmod(path, mode, follow_symlinks=False)
.Availability: Unix.
Changed in version 3.6: Accepts a path-like object.
-
os.
lchown
(path, uid, gid)¶ Change the owner and group id of path to the numeric uid and gid. This function will not follow symbolic links. As of Python 3.3, this is equivalent to
os.chown(path, uid, gid, follow_symlinks=False)
.Availability: Unix.
Changed in version 3.6: Accepts a path-like object.
-
os.
link
(src, dst, *, src_dir_fd=None, dst_dir_fd=None, follow_symlinks=True)¶ Create a hard link pointing to src named dst.
This function can support specifying src_dir_fd and/or dst_dir_fd to supply paths relative to directory descriptors, and not following symlinks.
Availability: Unix, Windows.
Changed in version 3.2: Added Windows support.
New in version 3.3: Added the src_dir_fd, dst_dir_fd, and follow_symlinks arguments.
Changed in version 3.6: Accepts a path-like object for src and dst.
-
os.
listdir
(path='.')¶ Return a list containing the names of the entries in the directory given by path. The list is in arbitrary order, and does not include the special entries
'.'
and'..'
even if they are present in the directory.path may be a path-like object. If path is of type
bytes
(directly or indirectly through thePathLike
interface), the filenames returned will also be of typebytes
; in all other circumstances, they will be of typestr
.This function can also support specifying a file descriptor; the file descriptor must refer to a directory.
Note
To encode
str
filenames tobytes
, usefsencode()
.See also
The
scandir()
function returns directory entries along with file attribute information, giving better performance for many common use cases.Changed in version 3.2: The path parameter became optional.
New in version 3.3: Added support for specifying an open file descriptor for path.
Changed in version 3.6: Accepts a path-like object.
-
os.
lstat
(path, *, dir_fd=None)¶ Perform the equivalent of an
lstat()
system call on the given path. Similar tostat()
, but does not follow symbolic links. Return astat_result
object.On platforms that do not support symbolic links, this is an alias for
stat()
.As of Python 3.3, this is equivalent to
os.stat(path, dir_fd=dir_fd, follow_symlinks=False)
.This function can also support paths relative to directory descriptors.
See also
The
stat()
function.Changed in version 3.2: Added support for Windows 6.0 (Vista) symbolic links.
Changed in version 3.3: Added the dir_fd parameter.
Changed in version 3.6: Accepts a path-like object for src and dst.
-
os.
mkdir
(path, mode=0o777, *, dir_fd=None)¶ Create a directory named path with numeric mode mode.
If the directory already exists,
FileExistsError
is raised.On some systems, mode is ignored. Where it is used, the current umask value is first masked out. If bits other than the last 9 (i.e. the last 3 digits of the octal representation of the mode) are set, their meaning is platform-dependent. On some platforms, they are ignored and you should call
chmod()
explicitly to set them.This function can also support paths relative to directory descriptors.
It is also possible to create temporary directories; see the
tempfile
module’stempfile.mkdtemp()
function.New in version 3.3: The dir_fd argument.
Changed in version 3.6: Accepts a path-like object.
-
os.
makedirs
(name, mode=0o777, exist_ok=False)¶ Recursive directory creation function. Like
mkdir()
, but makes all intermediate-level directories needed to contain the leaf directory.The mode parameter is passed to
mkdir()
for creating the leaf directory; see the mkdir() description for how it is interpreted. To set the file permission bits of any newly-created parent directories you can set the umask before invokingmakedirs()
. The file permission bits of existing parent directories are not changed.If exist_ok is
False
(the default), anFileExistsError
is raised if the target directory already exists.Note
makedirs()
will become confused if the path elements to create includepardir
(eg. “..” on UNIX systems).This function handles UNC paths correctly.
New in version 3.2: The exist_ok parameter.
Changed in version 3.4.1: Before Python 3.4.1, if exist_ok was
True
and the directory existed,makedirs()
would still raise an error if mode did not match the mode of the existing directory. Since this behavior was impossible to implement safely, it was removed in Python 3.4.1. See bpo-21082.Changed in version 3.6: Accepts a path-like object.
Changed in version 3.7: The mode argument no longer affects the file permission bits of newly-created intermediate-level directories.
-
os.
mkfifo
(path, mode=0o666, *, dir_fd=None)¶ Create a FIFO (a named pipe) named path with numeric mode mode. The current umask value is first masked out from the mode.
This function can also support paths relative to directory descriptors.
FIFOs are pipes that can be accessed like regular files. FIFOs exist until they are deleted (for example with
os.unlink()
). Generally, FIFOs are used as rendezvous between “client” and “server” type processes: the server opens the FIFO for reading, and the client opens it for writing. Note thatmkfifo()
doesn’t open the FIFO — it just creates the rendezvous point.Availability: Unix.
New in version 3.3: The dir_fd argument.
Changed in version 3.6: Accepts a 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
, andstat.S_IFIFO
(those constants are available instat
). Forstat.S_IFCHR
andstat.S_IFBLK
, device defines the newly created device special file (probably usingos.makedev()
), otherwise it is ignored.This function can also support paths relative to directory descriptors.
Availability: Unix.
New in version 3.3: The dir_fd argument.
Changed in version 3.6: Accepts a path-like object.
-
os.
major
(device)¶ Extract the device major number from a raw device number (usually the
st_dev
orst_rdev
field fromstat
).
-
os.
minor
(device)¶ Extract the device minor number from a raw device number (usually the
st_dev
orst_rdev
field fromstat
).
-
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
is raised. If a specific value for name is not supported by the host system, even if it is included inpathconf_names
, anOSError
is raised witherrno.EINVAL
for the error number.This function can support specifying a file descriptor.
Availability: Unix.
Changed in version 3.6: Accepts a path-like object.
-
os.
pathconf_names
¶ Dictionary mapping names accepted by
pathconf()
andfpathconf()
to the integer values defined for those names by the host operating system. This can be used to determine the set of names known to the system.Availability: Unix.
-
os.
readlink
(path, *, dir_fd=None)¶ Return a string representing the path to which the symbolic link points. The result may be either an absolute or relative pathname; if it is relative, it may be converted to an absolute pathname using
os.path.join(os.path.dirname(path), result)
.If the path is a string object (directly or indirectly through a
PathLike
interface), the result will also be a string object, and the call may raise a UnicodeDecodeError. If the path is a bytes object (direct or indirectly), the result will be a bytes object.This function can also support paths relative to directory descriptors.
Availability: Unix, Windows.
Changed in version 3.2: Added support for Windows 6.0 (Vista) symbolic links.
New in version 3.3: The dir_fd argument.
Changed in version 3.6: Accepts a path-like object.
-
os.
remove
(path, *, dir_fd=None)¶ Remove (delete) the file path. If path is a directory, an
IsADirectoryError
is raised. Usermdir()
to remove directories.This function can support paths relative to directory descriptors.
On Windows, attempting to remove a file that is in use causes an exception to be raised; on Unix, the directory entry is removed but the storage allocated to the file is not made available until the original file is no longer in use.
This function is semantically identical to
unlink()
.New in version 3.3: The dir_fd argument.
Changed in version 3.6: Accepts a path-like object.
-
os.
removedirs
(name)¶ Remove directories recursively. Works like
rmdir()
except that, if the leaf directory is successfully removed,removedirs()
tries to successively remove every parent directory mentioned in path until an error is raised (which is ignored, because it generally means that a parent directory is not empty). For example,os.removedirs('foo/bar/baz')
will first remove the directory'foo/bar/baz'
, and then remove'foo/bar'
and'foo'
if they are empty. RaisesOSError
if the leaf directory could not be successfully removed.Changed in version 3.6: Accepts a 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 exists, the operation will fail with an
OSError
subclass in a number of cases:On Windows, if dst exists a
FileExistsError
is always raised.On Unix, if src is a file and dst is a directory or vice-versa, an
IsADirectoryError
or aNotADirectoryError
will be raised respectively. If both are directories and dst is empty, dst will be silently replaced. If dst is a non-empty directory, anOSError
is raised. If both are files, dst it will be replaced silently if the user has permission. The operation may fail on some Unix flavors if src and dst are on different filesystems. If successful, the renaming will be an atomic operation (this is a POSIX requirement).This function can support specifying src_dir_fd and/or dst_dir_fd to supply paths relative to directory descriptors.
If you want cross-platform overwriting of the destination, use
replace()
.New in version 3.3: The src_dir_fd and dst_dir_fd arguments.
Changed in version 3.6: Accepts a path-like object for src and dst.
-
os.
renames
(old, new)¶ Recursive directory or file renaming function. Works like
rename()
, except creation of any intermediate directories needed to make the new pathname good is attempted first. After the rename, directories corresponding to rightmost path segments of the old name will be pruned away usingremovedirs()
.Note
This function can fail with the new directory structure made if you lack permissions needed to remove the leaf directory or file.
Changed in version 3.6: Accepts a path-like object for old and new.
-
os.
replace
(src, dst, *, src_dir_fd=None, dst_dir_fd=None)¶ Rename the file or directory src to dst. If dst is a directory,
OSError
will be raised. If dst exists and is a file, it will be replaced silently if the user has permission. The operation may fail if src and dst are on different filesystems. If successful, the renaming will be an atomic operation (this is a POSIX requirement).This function can support specifying src_dir_fd and/or dst_dir_fd to supply paths relative to directory descriptors.
New in version 3.3.
Changed in version 3.6: Accepts a path-like object for src and dst.
-
os.
rmdir
(path, *, dir_fd=None)¶ Remove (delete) the directory path. If the directory does not exist or is not empty, an
FileNotFoundError
or anOSError
is raised respectively. In order to remove whole directory trees,shutil.rmtree()
can be used.This function can support paths relative to directory descriptors.
New in version 3.3: The dir_fd parameter.
Changed in version 3.6: Accepts a path-like object.
-
os.
scandir
(path='.')¶ Return an iterator of
os.DirEntry
objects corresponding to the entries in the directory given by path. The entries are yielded in arbitrary order, and the special entries'.'
and'..'
are not included.Using
scandir()
instead oflistdir()
can significantly increase the performance of code that also needs file type or file attribute information, becauseos.DirEntry
objects expose this information if the operating system provides it when scanning a directory. Allos.DirEntry
methods may perform a system call, butis_dir()
andis_file()
usually only require a system call for symbolic links;os.DirEntry.stat()
always requires a system call on Unix but only requires one for symbolic links on Windows.path may be a path-like object. If path is of type
bytes
(directly or indirectly through thePathLike
interface), the type of thename
andpath
attributes of eachos.DirEntry
will bebytes
; in all other circumstances, they will be of typestr
.This function can also support specifying a file descriptor; the file descriptor must refer to a directory.
The
scandir()
iterator supports the context manager protocol and has the following method:-
scandir.
close
()¶ Close the iterator and free acquired resources.
This is called automatically when the iterator is exhausted or garbage collected, or when an error happens during iterating. However it is advisable to call it explicitly or use the
with
statement.New in version 3.6.
The following example shows a simple use of
scandir()
to display all the files (excluding directories) in the given path that don’t start with'.'
. Theentry.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)
Note
On Unix-based systems,
scandir()
uses the system’s opendir() and readdir() functions. On Windows, it uses the Win32 FindFirstFileW and FindNextFileW functions.New in version 3.5.
New in version 3.6: Added support for the context manager protocol and the
close()
method. If ascandir()
iterator is neither exhausted nor explicitly closed aResourceWarning
will be emitted in its destructor.The function accepts a path-like object.
Changed in version 3.7: Added support for file descriptors on Unix.
-
-
class
os.
DirEntry
¶ Object yielded by
scandir()
to expose the file path and other file attributes of a directory entry.scandir()
will provide as much of this information as possible without making additional system calls. When astat()
orlstat()
system call is made, theos.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 callingscandir()
, callos.stat(entry.path)
to fetch up-to-date information.Because the
os.DirEntry
methods can make operating system calls, they may also raiseOSError
. If you need very fine-grained control over errors, you can catchOSError
when calling one of theos.DirEntry
methods and handle as appropriate.To be directly usable as a path-like object,
os.DirEntry
implements thePathLike
interface.Attributes and methods on a
os.DirEntry
instance are as follows:-
name
¶ The entry’s base filename, relative to the
scandir()
path argument.The
name
attribute will bebytes
if thescandir()
path argument is of typebytes
andstr
otherwise. Usefsdecode()
to decode byte filenames.
-
path
¶ The entry’s full path name: equivalent to
os.path.join(scandir_path, entry.name)
where scandir_path is thescandir()
path argument. The path is only absolute if thescandir()
path argument was absolute. If thescandir()
path argument was a file descriptor, thepath
attribute is the same as thename
attribute.The
path
attribute will bebytes
if thescandir()
path argument is of typebytes
andstr
otherwise. Usefsdecode()
to decode byte filenames.
-
inode
()¶ Return the inode number of the entry.
The result is cached on the
os.DirEntry
object. Useos.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; returnFalse
if the entry is or points to any other kind of file, or if it doesn’t exist anymore.If follow_symlinks is
False
, returnTrue
only if this entry is a directory (without following symlinks); returnFalse
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_symlinksTrue
andFalse
. Callos.stat()
along withstat.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 isFalse
.This method can raise
OSError
, such asPermissionError
, butFileNotFoundError
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; returnFalse
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
, returnTrue
only if this entry is a file (without following symlinks); returnFalse
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 peris_dir()
.
-
is_symlink
()¶ Return
True
if this entry is a symbolic link (even if broken); returnFalse
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. Callos.path.islink()
to fetch up-to-date information.On the first, uncached call, no system call is required in most cases. Specifically, neither Windows or Unix require a system call, except on certain Unix file systems, such as network file systems, that return
dirent.d_type == DT_UNKNOWN
.This method can raise
OSError
, such asPermissionError
, butFileNotFoundError
is caught and not raised.
-
stat
(*, follow_symlinks=True)¶ Return a
stat_result
object for this entry. This method follows symbolic links by default; to stat a symbolic link add thefollow_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
andst_nlink
attributes of thestat_result
are always set to zero. Callos.stat()
to get these attributes.The result is cached on the
os.DirEntry
object, with a separate cache for follow_symlinksTrue
andFalse
. Callos.stat()
to fetch up-to-date information.
Note that there is a nice correspondence between several attributes and methods of
os.DirEntry
and ofpathlib.Path
. In particular, thename
attribute has the same meaning, as do theis_dir()
,is_file()
,is_symlink()
andstat()
methods.New in version 3.5.
-
-
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 thePathLike
interface – or as an open file descriptor. Return astat_result
object.This function normally follows symlinks; to stat a symlink add the argument
follow_symlinks=False
, or uselstat()
.This function can support specifying a file descriptor and not following symlinks.
Example:
>>> 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
New in version 3.3: Added the dir_fd and follow_symlinks arguments, specifying a file descriptor instead of a path.
Changed in version 3.6: Accepts a 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 ofos.stat()
,os.fstat()
andos.lstat()
.Attributes:
-
st_mode
¶ File mode: file type and file mode bits (permissions).
-
st_ino
¶ Platform dependent, but if non-zero, uniquely identifies the file for a given value of
st_dev
. Typically:the inode number on Unix,
the file index on Windows
-
st_dev
¶ Identifier of the device on which this file resides.
-
st_nlink
¶ Number of hard links.
-
st_uid
¶ User identifier of the file owner.
-
st_gid
¶ Group identifier of the file owner.
-
st_size
¶ Size of the file in bytes, if it is a regular file or a symbolic link. The size of a symbolic link is the length of the pathname it contains, without a terminating null byte.
Timestamps:
-
st_atime
¶ Time of most recent access expressed in seconds.
-
st_mtime
¶ Time of most recent content modification expressed in seconds.
-
st_ctime
¶ Platform dependent:
the time of most recent metadata change on Unix,
the time of creation on Windows, expressed in seconds.
-
st_atime_ns
¶ Time of most recent access expressed in nanoseconds as an integer.
-
st_mtime_ns
¶ Time of most recent content modification expressed in nanoseconds as an integer.
-
st_ctime_ns
¶ Platform dependent:
the time of most recent metadata change on Unix,
the time of creation on Windows, expressed in nanoseconds as an integer.
Note
The exact meaning and resolution of the
st_atime
,st_mtime
, andst_ctime
attributes depend on the operating system and the file system. For example, on Windows systems using the FAT or FAT32 file systems,st_mtime
has 2-second resolution, andst_atime
has only 1-day resolution. See your operating system documentation for details.Similarly, although
st_atime_ns
,st_mtime_ns
, andst_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 storest_atime
,st_mtime
, andst_ctime
cannot preserve all of it, and as such will be slightly inexact. If you need the exact timestamps you should always usest_atime_ns
,st_mtime_ns
, andst_ctime_ns
.On some Unix systems (such as Linux), the following attributes may also be available:
-
st_blocks
¶ Number of 512-byte blocks allocated for file. This may be smaller than
st_size
/512 when the file has holes.
-
st_blksize
¶ “Preferred” blocksize for efficient file system I/O. Writing to a file in smaller chunks may cause an inefficient read-modify-rewrite.
-
st_rdev
¶ Type of device if an inode device.
-
st_flags
¶ User defined flags for file.
On other Unix systems (such as FreeBSD), the following attributes may be available (but may be only filled out if root tries to use them):
-
st_gen
¶ File generation number.
-
st_birthtime
¶ Time of file creation.
On Solaris and derivatives, the following attributes may also be available:
-
st_fstype
¶ String that uniquely identifies the type of the filesystem that contains the file.
On Mac OS systems, the following attributes may also be available:
-
st_rsize
¶ Real size of the file.
-
st_creator
¶ Creator of the file.
-
st_type
¶ File type.
On Windows systems, the following attribute is also available:
-
st_file_attributes
¶ Windows file attributes:
dwFileAttributes
member of theBY_HANDLE_FILE_INFORMATION
structure returned byGetFileInformationByHandle()
. See theFILE_ATTRIBUTE_*
constants in thestat
module.
The standard module
stat
defines functions and constants that are useful for extracting information from astat
structure. (On Windows, some items are filled with dummy values.)For backward compatibility, a
stat_result
instance is also accessible as a tuple of at least 10 integers giving the most important (and portable) members of thestat
structure, in the orderst_mode
,st_ino
,st_dev
,st_nlink
,st_uid
,st_gid
,st_size
,st_atime
,st_mtime
,st_ctime
. More items may be added at the end by some implementations. For compatibility with older Python versions, accessingstat_result
as a tuple always returns integers.New in version 3.3: Added the
st_atime_ns
,st_mtime_ns
, andst_ctime_ns
members.New in version 3.5: Added the
st_file_attributes
member on Windows.Changed in version 3.5: Windows now returns the file index as
st_ino
when available.New in version 3.7: Added the
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 thestatvfs
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: ifST_RDONLY
is set, the filesystem is mounted read-only, and ifST_NOSUID
is set, the semantics of setuid/setgid bits are disabled or not supported.Additional module-level constants are defined for GNU/glibc based systems. These are
ST_NODEV
(disallow access to device special files),ST_NOEXEC
(disallow program execution),ST_SYNCHRONOUS
(writes are synced at once),ST_MANDLOCK
(allow mandatory locks on an FS),ST_WRITE
(write on file/directory/symlink),ST_APPEND
(append-only file),ST_IMMUTABLE
(immutable file),ST_NOATIME
(do not update access times),ST_NODIRATIME
(do not update directory access times),ST_RELATIME
(update atime relative to mtime/ctime).This function can support specifying a file descriptor.
Availability: Unix.
Changed in version 3.2: The
ST_RDONLY
andST_NOSUID
constants were added.New in version 3.3: Added support for specifying an open file descriptor for path.
Changed in version 3.4: The
ST_NODEV
,ST_NOEXEC
,ST_SYNCHRONOUS
,ST_MANDLOCK
,ST_WRITE
,ST_APPEND
,ST_IMMUTABLE
,ST_NOATIME
,ST_NODIRATIME
, andST_RELATIME
constants were added.Changed in version 3.6: Accepts a path-like object.
New in version 3.7: Added
f_fsid
.
-
os.
supports_dir_fd
¶ A
Set
object indicating which functions in theos
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 onsupports_dir_fd
. As an example, this expression determines whether the dir_fd parameter ofos.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.
New in version 3.3.
-
os.
supports_effective_ids
¶ A
Set
object indicating which functions in theos
module permit use of the effective_ids parameter foros.access()
. If the local platform supports it, the collection will containos.access()
, otherwise it will be empty.To check whether you can use the effective_ids parameter for
os.access()
, use thein
operator onsupports_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.
New in version 3.3.
-
os.
supports_fd
¶ A
Set
object indicating which functions in theos
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 onsupports_fd
. As an example, this expression determines whetheros.chdir()
accepts open file descriptors when called on your local platform:os.chdir in os.supports_fd
New in version 3.3.
-
os.
supports_follow_symlinks
¶ A
Set
object indicating which functions in theos
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 onsupports_follow_symlinks
. As an example, this expression determines whether the follow_symlinks parameter ofos.stat()
is locally available:os.stat in os.supports_follow_symlinks
New in version 3.3.
-
os.
symlink
(src, dst, target_is_directory=False, *, dir_fd=None)¶ Create a symbolic link pointing to src named dst.
On Windows, a symlink represents either a file or a directory, and does not morph to the target dynamically. If the target is present, the type of the symlink will be created to match. Otherwise, the symlink will be created as a directory if target_is_directory is
True
or a file symlink (the default) otherwise. On non-Windows platforms, target_is_directory is ignored.Symbolic link support was introduced in Windows 6.0 (Vista).
symlink()
will raise aNotImplementedError
on Windows versions earlier than 6.0.This function can support paths relative to directory descriptors.
Note
On Windows, the SeCreateSymbolicLinkPrivilege is required in order to successfully create symlinks. This privilege is not typically granted to regular users but is available to accounts which can escalate privileges to the administrator level. Either obtaining the privilege or running your application as an administrator are ways to successfully create symlinks.
OSError
is raised when the function is called by an unprivileged user.Availability: Unix, Windows.
Changed in version 3.2: Added support for Windows 6.0 (Vista) symbolic links.
New in version 3.3: Added the dir_fd argument, and now allow target_is_directory on non-Windows platforms.
Changed in version 3.6: Accepts a path-like object for src and dst.
-
os.
sync
()¶ Force write of everything to disk.
Availability: Unix.
New in version 3.3.
-
os.
truncate
(path, length)¶ Truncate the file corresponding to path, so that it is at most length bytes in size.
This function can support specifying a file descriptor.
Availability: Unix, Windows.
New in version 3.3.
Changed in version 3.5: Added support for Windows
Changed in version 3.6: Accepts a path-like object.
-
os.
unlink
(path, *, dir_fd=None)¶ Remove (delete) the file path. This function is semantically identical to
remove()
; theunlink
name is its traditional Unix name. Please see the documentation forremove()
for further information.New in version 3.3: The dir_fd parameter.
Changed in version 3.6: Accepts a path-like object.
-
os.
utime
(path, times=None, *, [ns, ]dir_fd=None, follow_symlinks=True)¶ Set the access and modified times of the file specified by path.
utime()
takes two optional parameters, times and ns. These specify the times set on path and are used as follows:If ns is specified, it must be a 2-tuple of the form
(atime_ns, mtime_ns)
where each member is an int expressing nanoseconds.If times is not
None
, it must be a 2-tuple of the form(atime, mtime)
where each member is an int or float expressing seconds.If times is
None
and ns is unspecified, this is equivalent to specifyingns=(atime_ns, mtime_ns)
where both times are the current time.
It is an error to specify tuples for both times and ns.
Whether a directory can be given for path depends on whether the operating system implements directories as files (for example, Windows does not). Note that the exact times you set here may not be returned by a subsequent
stat()
call, depending on the resolution with which your operating system records access and modification times; seestat()
. The best way to preserve exact times is to use the st_atime_ns and st_mtime_ns fields from theos.stat()
result object with the ns parameter to utime.This function can support specifying a file descriptor, paths relative to directory descriptors and not following symlinks.
New in version 3.3: Added support for specifying an open file descriptor for path, and the dir_fd, follow_symlinks, and ns parameters.
Changed in version 3.6: Accepts a 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, doos.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 isFalse
, 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 usingdel
or slice assignment), andwalk()
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 informwalk()
about directories the caller creates or renames before it resumeswalk()
again. Modifying dirnames when topdown isFalse
has no effect on the behavior of the walk, because in bottom-up mode the directories in dirnames are generated before dirpath itself is generated.By default, errors from the
scandir()
call are ignored. If optional argument onerror is specified, it should be a function; it will be called with one argument, anOSError
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 thefilename
attribute of the exception object.By default,
walk()
will not walk down into symbolic links that resolve to directories. Set followlinks toTrue
to visit directories pointed to by symlinks, on systems that support them.Note
Be aware that setting followlinks to
True
can lead to infinite recursion if a link points to a parent directory of itself.walk()
does not keep track of the directories it visited already.Note
If you pass a relative pathname, don’t change the current working directory between resumptions of
walk()
.walk()
never changes the current directory, and assumes that its caller doesn’t either.This example displays the number of bytes taken by non-directory files in each directory under the starting directory, except that it doesn’t look under any CVS subdirectory:
import os from os.path import join, getsize for root, dirs, files in os.walk('python/Lib/email'): print(root, "consumes", end=" ") print(sum(getsize(join(root, name)) for name in files), end=" ") print("bytes in", len(files), "non-directory files") if 'CVS' in dirs: dirs.remove('CVS') # don't visit CVS directories
In the next example (simple implementation of
shutil.rmtree()
), walking the tree bottom-up is essential,rmdir()
doesn’t allow deleting a directory before the directory is empty:# Delete everything reachable from the directory named in "top", # assuming there are no symbolic links. # CAUTION: This is dangerous! For example, if top == '/', it # could delete all your disk files. import os for root, dirs, files in os.walk(top, topdown=False): for name in files: os.remove(os.path.join(root, name)) for name in dirs: os.rmdir(os.path.join(root, name))
Changed in version 3.5: This function now calls
os.scandir()
instead ofos.listdir()
, making it faster by reducing the number of calls toos.stat()
.Changed in version 3.6: Accepts a path-like object.
-
os.
fwalk
(top='.', topdown=True, onerror=None, *, follow_symlinks=False, dir_fd=None)¶ This behaves exactly like
walk()
, except that it yields a 4-tuple(dirpath, dirnames, filenames, dirfd)
, and it supportsdir_fd
.dirpath, dirnames and filenames are identical to
walk()
output, and dirfd is a file descriptor referring to the directory dirpath.This function always supports paths relative to directory descriptors and not following symlinks. Note however that, unlike other functions, the
fwalk()
default value for follow_symlinks isFalse
.Note
Since
fwalk()
yields file descriptors, those are only valid until the next iteration step, so you should duplicate them (e.g. withdup()
) if you want to keep them longer.This example displays the number of bytes taken by non-directory files in each directory under the starting directory, except that it doesn’t look under any CVS subdirectory:
import os for root, dirs, files, rootfd in os.fwalk('python/Lib/email'): print(root, "consumes", end="") print(sum([os.stat(name, dir_fd=rootfd).st_size for name in files]), end="") print("bytes in", len(files), "non-directory files") if 'CVS' in dirs: dirs.remove('CVS') # don't visit CVS directories
In the next example, walking the tree bottom-up is essential:
rmdir()
doesn’t allow deleting a directory before the directory is empty:# Delete everything reachable from the directory named in "top", # assuming there are no symbolic links. # CAUTION: This is dangerous! For example, if top == '/', it # could delete all your disk files. import os for root, dirs, files, rootfd in os.fwalk(top, topdown=False): for name in files: os.unlink(name, dir_fd=rootfd) for name in dirs: os.rmdir(name, dir_fd=rootfd)
Availability: Unix.
New in version 3.3.
Changed in version 3.6: Accepts a path-like object.
Changed in version 3.7: Added support for
bytes
paths.
Linux extended attributes¶
New in version 3.3.
These functions are all available on Linux only.
-
os.
getxattr
(path, attribute, *, follow_symlinks=True)¶ Return the value of the extended filesystem attribute attribute for path. attribute can be bytes or str (directly or indirectly through the
PathLike
interface). If it is str, it is encoded with the filesystem encoding.This function can support specifying a file descriptor and not following symlinks.
Changed in version 3.6: Accepts a path-like object for path and attribute.
-
os.
listxattr
(path=None, *, follow_symlinks=True)¶ Return a list of the extended filesystem attributes on path. The attributes in the list are represented as strings decoded with the filesystem encoding. If path is
None
,listxattr()
will examine the current directory.This function can support specifying a file descriptor and not following symlinks.
Changed in version 3.6: Accepts a path-like object.
-
os.
removexattr
(path, attribute, *, follow_symlinks=True)¶ Removes the extended filesystem attribute attribute from path. attribute should be bytes or str (directly or indirectly through the
PathLike
interface). If it is a string, it is encoded with the filesystem encoding.This function can support specifying a file descriptor and not following symlinks.
Changed in version 3.6: Accepts a path-like object for path and attribute.
-
os.
setxattr
(path, attribute, value, flags=0, *, follow_symlinks=True)¶ Set the extended filesystem attribute attribute on path to value. attribute must be a bytes or str with no embedded NULs (directly or indirectly through the
PathLike
interface). If it is a str, it is encoded with the filesystem encoding. flags may beXATTR_REPLACE
orXATTR_CREATE
. IfXATTR_REPLACE
is given and the attribute does not exist,EEXISTS
will be raised. IfXATTR_CREATE
is given and the attribute already exists, the attribute will not be created andENODATA
will be raised.This function can support specifying a file descriptor and not following symlinks.
Note
A bug in Linux kernel versions less than 2.6.39 caused the flags argument to be ignored on some filesystems.
Changed in version 3.6: Accepts a path-like object for path and attribute.
-
os.
XATTR_SIZE_MAX
¶ The maximum size the value of an extended attribute can be. Currently, this is 64 KiB on Linux.
-
os.
XATTR_CREATE
¶ This is a possible value for the flags argument in
setxattr()
. It indicates the operation must create an attribute.
-
os.
XATTR_REPLACE
¶ This is a possible value for the flags argument in
setxattr()
. It indicates the operation must replace an existing attribute.
Process Management¶
These functions may be used to create and manage processes.
The various exec*
functions take a list of arguments for the new
program loaded into the process. In each case, the first of these arguments is
passed to the new program as its own name rather than as an argument a user may
have typed on a command line. For the C programmer, this is the argv[0]
passed to a program’s main()
. For example, os.execv('/bin/echo',
['foo', 'bar'])
will only print bar
on standard output; foo
will seem
to be ignored.
-
os.
abort
()¶ Generate a
SIGABRT
signal to the current process. On Unix, the default behavior is to produce a core dump; on Windows, the process immediately returns an exit code of3
. Be aware that calling this function will not call the Python signal handler registered forSIGABRT
withsignal.signal()
.
-
os.
execl
(path, arg0, arg1, ...)¶ -
os.
execle
(path, arg0, arg1, ..., env)¶ -
os.
execlp
(file, arg0, arg1, ...)¶ -
os.
execlpe
(file, arg0, arg1, ..., env)¶ -
os.
execv
(path, args)¶ -
os.
execve
(path, args, env)¶ -
os.
execvp
(file, args)¶ -
os.
execvpe
(file, args, env)¶ These functions all execute a new program, replacing the current process; they do not return. On Unix, the new executable is loaded into the current process, and will have the same process id as the caller. Errors will be reported as
OSError
exceptions.The current process is replaced immediately. Open file objects and descriptors are not flushed, so if there may be data buffered on these open files, you should flush them using
sys.stdout.flush()
oros.fsync()
before calling anexec*
function.The “l” and “v” variants of the
exec*
functions differ in how command-line arguments are passed. The “l” variants are perhaps the easiest to work with if the number of parameters is fixed when the code is written; the individual parameters simply become additional parameters to theexecl*()
functions. The “v” variants are good when the number of parameters is variable, with the arguments being passed in a list or tuple as the args parameter. In either case, the arguments to the child process should start with the name of the command being run, but this is not enforced.The variants which include a “p” near the end (
execlp()
,execlpe()
,execvp()
, andexecvpe()
) will use thePATH
environment variable to locate the program file. When the environment is being replaced (using one of theexec*e
variants, discussed in the next paragraph), the new environment is used as the source of thePATH
variable. The other variants,execl()
,execle()
,execv()
, andexecve()
, will not use thePATH
variable to locate the executable; path must contain an appropriate absolute or relative path.For
execle()
,execlpe()
,execve()
, andexecvpe()
(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 functionsexecl()
,execlp()
,execv()
, andexecvp()
all cause the new process to inherit the environment of the current process.For
execve()
on some platforms, path may also be specified as an open file descriptor. This functionality may not be supported on your platform; you can check whether or not it is available usingos.supports_fd
. If it is unavailable, using it will raise aNotImplementedError
.Availability: Unix, Windows.
New in version 3.3: Added support for specifying an open file descriptor for path for
execve()
.Changed in version 3.6: Accepts a path-like object.
-
os.
_exit
(n)¶ Exit the process with status n, without calling cleanup handlers, flushing stdio buffers, etc.
The following exit codes are defined and can be used with _exit()
,
although they are not required. These are typically used for system programs
written in Python, such as a mail server’s external command delivery program.
Note
Some of these may not be available on all Unix platforms, since there is some variation. These constants are defined where they are defined by the underlying platform.
-
os.
EX_OK
¶ Exit code that means no error occurred.
Availability: Unix.
-
os.
EX_USAGE
¶ Exit code that means the command was used incorrectly, such as when the wrong number of arguments are given.
Availability: Unix.
-
os.
EX_DATAERR
¶ Exit code that means the input data was incorrect.
Availability: Unix.
-
os.
EX_NOINPUT
¶ Exit code that means an input file did not exist or was not readable.
Availability: Unix.
-
os.
EX_NOUSER
¶ Exit code that means a specified user did not exist.
Availability: Unix.
-
os.
EX_NOHOST
¶ Exit code that means a specified host did not exist.
Availability: Unix.
-
os.
EX_UNAVAILABLE
¶ Exit code that means that a required service is unavailable.
Availability: Unix.
-
os.
EX_SOFTWARE
¶ Exit code that means an internal software error was detected.
Availability: Unix.
-
os.
EX_OSERR
¶ Exit code that means an operating system error was detected, such as the inability to fork or create a pipe.
Availability: Unix.
-
os.
EX_OSFILE
¶ Exit code that means some system file did not exist, could not be opened, or had some other kind of error.
Availability: Unix.
-
os.
EX_CANTCREAT
¶ Exit code that means a user specified output file could not be created.
Availability: Unix.
-
os.
EX_IOERR
¶ Exit code that means that an error occurred while doing I/O on some file.
Availability: Unix.
-
os.
EX_TEMPFAIL
¶ Exit code that means a temporary failure occurred. This indicates something that may not really be an error, such as a network connection that couldn’t be made during a retryable operation.
Availability: Unix.
-
os.
EX_PROTOCOL
¶ Exit code that means that a protocol exchange was illegal, invalid, or not understood.
Availability: Unix.
-
os.
EX_NOPERM
¶ Exit code that means that there were insufficient permissions to perform the operation (but not intended for file system problems).
Availability: Unix.
-
os.
EX_CONFIG
¶ Exit code that means that some kind of configuration error occurred.
Availability: Unix.
-
os.
EX_NOTFOUND
¶ Exit code that means something like “an entry was not found”.
Availability: Unix.
-
os.
fork
()¶ Fork a child process. Return
0
in the child and the child’s process id in the parent. If an error occursOSError
is raised.Note that some platforms including FreeBSD <= 6.3 and Cygwin have known issues when using fork() from a thread.
Warning
See
ssl
for applications that use the SSL module with fork().Availability: Unix.
-
os.
forkpty
()¶ Fork a child process, using a new pseudo-terminal as the child’s controlling terminal. Return a pair of
(pid, fd)
, where pid is0
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 thepty
module. If an error occursOSError
is raised.Availability: some flavors of Unix.
-
os.
kill
(pid, sig)¶ Send signal sig to the process pid. Constants for the specific signals available on the host platform are defined in the
signal
module.Windows: The
signal.CTRL_C_EVENT
andsignal.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 ofkill()
additionally takes process handles to be killed.See also
signal.pthread_kill()
.New in version 3.2: Windows support.
-
os.
killpg
(pgid, sig)¶ Send the signal sig to the process group pgid.
Availability: Unix.
-
os.
nice
(increment)¶ Add increment to the process’s “niceness”. Return the new niceness.
Availability: Unix.
-
os.
plock
(op)¶ Lock program segments into memory. The value of op (defined in
<sys/lock.h>
) determines which segments are locked.Availability: Unix.
-
os.
popen
(cmd, mode='r', buffering=-1)¶ Open a pipe to or from command cmd. The return value is an open file object connected to the pipe, which can be read or written depending on whether mode is
'r'
(default) or'w'
. The buffering argument has the same meaning as the corresponding argument to the built-inopen()
function. The returned file object reads or writes text strings rather than bytes.The
close
method returnsNone
if the subprocess exited successfully, or the subprocess’s return code if there was an error. On POSIX systems, if the return code is positive it represents the return value of the process left-shifted by one byte. If the return code is negative, the process was terminated by the signal given by the negated value of the return code. (For example, the return value might be- signal.SIGKILL
if the subprocess was killed.) On Windows systems, the return value contains the signed integer return code from the child process.This is implemented using
subprocess.Popen
; see that class’s documentation for more powerful ways to manage and communicate with subprocesses.
-
os.
register_at_fork
(*, before=None, after_in_parent=None, after_in_child=None)¶ Register callables to be executed when a new child process is forked using
os.fork()
or similar process cloning APIs. The parameters are optional and keyword-only. Each specifies a different call point.before is a function called before forking a child process.
after_in_parent is a function called from the parent process after forking a child process.
after_in_child is a function called from the child process.
These calls are only made if control is expected to return to the Python interpreter. A typical
subprocess
launch will not trigger them as the child is not going to re-enter the interpreter.Functions registered for execution before forking are called in reverse registration order. Functions registered for execution after forking (either in the parent or in the child) are called in registration order.
Note that
fork()
calls made by third-party C code may not call those functions, unless it explicitly callsPyOS_BeforeFork()
,PyOS_AfterFork_Parent()
andPyOS_AfterFork_Child()
.There is no way to unregister a function.
Availability: Unix.
New in version 3.7.
-
os.
spawnl
(mode, path, ...)¶ -
os.
spawnle
(mode, path, ..., env)¶ -
os.
spawnlp
(mode, file, ...)¶ -
os.
spawnlpe
(mode, file, ..., env)¶ -
os.
spawnv
(mode, path, args)¶ -
os.
spawnve
(mode, path, args, env)¶ -
os.
spawnvp
(mode, file, args)¶ -
os.
spawnvpe
(mode, file, args, env)¶ Execute the program path in a new process.
(Note that the
subprocess
module provides more powerful facilities for spawning new processes and retrieving their results; using that module is preferable to using these functions. Check especially the Replacing Older Functions with the subprocess Module section.)If mode is
P_NOWAIT
, this function returns the process id of the new process; if mode isP_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 thewaitpid()
function.The “l” and “v” variants of the
spawn*
functions differ in how command-line arguments are passed. The “l” variants are perhaps the easiest to work with if the number of parameters is fixed when the code is written; the individual parameters simply become additional parameters to thespawnl*()
functions. The “v” variants are good when the number of parameters is variable, with the arguments being passed in a list or tuple as the args parameter. In either case, the arguments to the child process must start with the name of the command being run.The variants which include a second “p” near the end (
spawnlp()
,spawnlpe()
,spawnvp()
, andspawnvpe()
) will use thePATH
environment variable to locate the program file. When the environment is being replaced (using one of thespawn*e
variants, discussed in the next paragraph), the new environment is used as the source of thePATH
variable. The other variants,spawnl()
,spawnle()
,spawnv()
, andspawnve()
, will not use thePATH
variable to locate the executable; path must contain an appropriate absolute or relative path.For
spawnle()
,spawnlpe()
,spawnve()
, andspawnvpe()
(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 functionsspawnl()
,spawnlp()
,spawnv()
, andspawnvp()
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 of127
.As an example, the following calls to
spawnlp()
andspawnvpe()
are equivalent:import os os.spawnlp(os.P_WAIT, 'cp', 'cp', 'index.html', '/dev/null') L = ['cp', 'index.html', '/dev/null'] os.spawnvpe(os.P_WAIT, 'cp', L, os.environ)
Availability: Unix, Windows.
spawnlp()
,spawnlpe()
,spawnvp()
andspawnvpe()
are not available on Windows.spawnle()
andspawnve()
are not thread-safe on Windows; we advise you to use thesubprocess
module instead.Changed in version 3.6: Accepts a path-like object.
-
os.
P_NOWAIT
¶ -
os.
P_NOWAITO
¶ Possible values for the mode parameter to the
spawn*
family of functions. If either of these values is given, thespawn*()
functions will return as soon as the new process has been created, with the process id as the return value.Availability: Unix, Windows.
-
os.
P_WAIT
¶ Possible value for the mode parameter to the
spawn*
family of functions. If this is given as mode, thespawn*()
functions will not return until the new process has run to completion and will return the exit code of the process the run is successful, or-signal
if a signal kills the process.Availability: Unix, Windows.
-
os.
P_DETACH
¶ -
os.
P_OVERLAY
¶ Possible values for the mode parameter to the
spawn*
family of functions. These are less portable than those listed above.P_DETACH
is similar toP_NOWAIT
, but the new process is detached from the console of the calling process. IfP_OVERLAY
is used, the current process will be replaced; thespawn*
function will not return.Availability: Windows.
-
os.
startfile
(path[, operation])¶ Start a file with its associated application.
When operation is not specified or
'open'
, this acts like double-clicking the file in Windows Explorer, or giving the file name as an argument to the start command from the interactive command shell: the file is opened with whatever application (if any) its extension is associated.When another operation is given, it must be a “command verb” that specifies what should be done with the file. Common verbs documented by Microsoft are
'print'
and'edit'
(to be used on files) as well as'explore'
and'find'
(to be used on directories).startfile()
returns as soon as the associated application is launched. There is no option to wait for the application to close, and no way to retrieve the application’s exit status. The path parameter is relative to the current directory. If you want to use an absolute path, make sure the first character is not a slash ('/'
); the underlying Win32ShellExecute()
function doesn’t work if it is. Use theos.path.normpath()
function to ensure that the path is properly encoded for Win32.To reduce interpreter startup overhead, the Win32
ShellExecute()
function is not resolved until this function is first called. If the function cannot be resolved,NotImplementedError
will be raised.Availability: Windows.
-
os.
system
(command)¶ Execute the command (a string) in a subshell. This is implemented by calling the Standard C function
system()
, and has the same limitations. Changes tosys.stdin
, etc. are not reflected in the environment of the executed command. If command generates any output, it will be sent to the interpreter standard output stream.On Unix, the return value is the exit status of the process encoded in the format specified for
wait()
. Note that POSIX does not specify the meaning of the return value of the Csystem()
function, so the return value of the Python function is system-dependent.On Windows, the return value is that returned by the system shell after running command. The shell is given by the Windows environment variable
COMSPEC
: it is usually cmd.exe, which returns the exit status of the command run; on systems using a non-native shell, consult your shell documentation.The
subprocess
module provides more powerful facilities for spawning new processes and retrieving their results; using that module is preferable to using this function. See the Replacing Older Functions with the subprocess Module section in thesubprocess
documentation for some helpful recipes.Availability: Unix, Windows.
-
os.
times
()¶ Returns the current global process times. The return value is an object with five attributes:
user
- user timesystem
- system timechildren_user
- user time of all child processeschildren_system
- system time of all child processeselapsed
- elapsed real time since a fixed point in the past
For backwards compatibility, this object also behaves like a five-tuple containing
user
,system
,children_user
,children_system
, andelapsed
in that order.See the Unix manual page times(2) or the corresponding Windows Platform API documentation. On Windows, only
user
andsystem
are known; the other attributes are zero.Availability: Unix, Windows.
Changed in version 3.3: Return type changed from a tuple to a tuple-like object with named attributes.
-
os.
wait
()¶ Wait for completion of a child process, and return a tuple containing its pid and exit status indication: a 16-bit number, whose low byte is the signal number that killed the process, and whose high byte is the exit status (if the signal number is zero); the high bit of the low byte is set if a core file was produced.
Availability: Unix.
-
os.
waitid
(idtype, id, options)¶ Wait for the completion of one or more child processes. idtype can be
P_PID
,P_PGID
orP_ALL
. id specifies the pid to wait on. options is constructed from the ORing of one or more ofWEXITED
,WSTOPPED
orWCONTINUED
and additionally may be ORed withWNOHANG
orWNOWAIT
. The return value is an object representing the data contained in thesiginfo_t
structure, namely:si_pid
,si_uid
,si_signo
,si_status
,si_code
orNone
ifWNOHANG
is specified and there are no children in a waitable state.Availability: Unix.
New in version 3.3.
-
os.
P_PID
¶ -
os.
P_PGID
¶ -
os.
P_ALL
¶ These are the possible values for idtype in
waitid()
. They affect how id is interpreted.Availability: Unix.
New in version 3.3.
-
os.
WEXITED
¶ -
os.
WSTOPPED
¶ -
os.
WNOWAIT
¶ Flags that can be used in options in
waitid()
that specify what child signal to wait for.Availability: Unix.
New in version 3.3.
-
os.
CLD_EXITED
¶ -
os.
CLD_DUMPED
¶ -
os.
CLD_TRAPPED
¶ -
os.
CLD_CONTINUED
¶ These are the possible values for
si_code
in the result returned bywaitid()
.Availability: Unix.
New in version 3.3.
-
os.
waitpid
(pid, options)¶ The details of this function differ on Unix and Windows.
On Unix: Wait for completion of a child process given by process id pid, and return a tuple containing its process id and exit status indication (encoded as for
wait()
). The semantics of the call are affected by the value of the integer options, which should be0
for normal operation.If pid is greater than
0
,waitpid()
requests status information for that specific process. If pid is0
, the request is for the status of any child in the process group of the current process. If pid is-1
, the request pertains to any child of the current process. If pid is less than-1
, status is requested for any process in the process group-pid
(the absolute value of pid).An
OSError
is raised with the value of errno when the syscall returns -1.On Windows: Wait for completion of a process given by process handle pid, and return a tuple containing pid, and its exit status shifted left by 8 bits (shifting makes cross-platform use of the function easier). A pid less than or equal to
0
has no special meaning on Windows, and raises an exception. The value of integer options has no effect. pid can refer to any process whose id is known, not necessarily a child process. Thespawn*
functions called withP_NOWAIT
return suitable process handles.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).
-
os.
wait3
(options)¶ Similar to
waitpid()
, except no process id argument is given and a 3-element tuple containing the child’s process id, exit status indication, and resource usage information is returned. Refer toresource
.getrusage()
for details on resource usage information. The option argument is the same as that provided towaitpid()
andwait4()
.Availability: Unix.
-
os.
wait4
(pid, options)¶ Similar to
waitpid()
, except a 3-element tuple, containing the child’s process id, exit status indication, and resource usage information is returned. Refer toresource
.getrusage()
for details on resource usage information. The arguments towait4()
are the same as those provided towaitpid()
.Availability: Unix.
-
os.
WNOHANG
¶ The option for
waitpid()
to return immediately if no child process status is available immediately. The function returns(0, 0)
in this case.Availability: Unix.
-
os.
WCONTINUED
¶ This option causes child processes to be reported if they have been continued from a job control stop since their status was last reported.
Availability: some Unix systems.
-
os.
WUNTRACED
¶ This option causes child processes to be reported if they have been stopped but their current state has not been reported since they were stopped.
Availability: Unix.
The following functions take a process status code as returned by
system()
, wait()
, or waitpid()
as a parameter. They may be
used to determine the disposition of a process.
-
os.
WCOREDUMP
(status)¶ Return
True
if a core dump was generated for the process, otherwise returnFalse
.Availability: Unix.
-
os.
WIFCONTINUED
(status)¶ Return
True
if the process has been continued from a job control stop, otherwise returnFalse
.Availability: Unix.
-
os.
WIFSTOPPED
(status)¶ Return
True
if the process has been stopped, otherwise returnFalse
.Availability: Unix.
-
os.
WIFSIGNALED
(status)¶ Return
True
if the process exited due to a signal, otherwise returnFalse
.Availability: Unix.
-
os.
WIFEXITED
(status)¶ Return
True
if the process exited using the exit(2) system call, otherwise returnFalse
.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.Availability: Unix.
-
os.
WSTOPSIG
(status)¶ Return the signal which caused the process to stop.
Availability: Unix.
-
os.
WTERMSIG
(status)¶ Return the signal which caused the process to exit.
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.
New in version 3.3.
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()
,sched_setscheduler()
, andsched_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
instance.
-
os.
sched_getscheduler
(pid)¶ Return the scheduling policy for the process with PID pid. A pid of 0 means the calling process. The result is one of the scheduling policy constants above.
-
os.
sched_setparam
(pid, param)¶ Set a scheduling parameters for the process with PID pid. A pid of 0 means the calling process. param is a
sched_param
instance.
-
os.
sched_getparam
(pid)¶ Return the scheduling parameters as a
sched_param
instance for the process with PID pid. A pid of 0 means the calling process.
-
os.
sched_rr_get_interval
(pid)¶ Return the round-robin quantum in seconds for the process with PID pid. A pid of 0 means the calling process.
-
os.
sched_yield
()¶ Voluntarily relinquish the CPU.
-
os.
sched_setaffinity
(pid, mask)¶ Restrict the process with PID pid (or the current process if zero) to a set of CPUs. mask is an iterable of integers representing the set of CPUs to which the process should be restricted.
-
os.
sched_getaffinity
(pid)¶ Return the set of CPUs the process with PID pid (or the current process if zero) is restricted to.
Miscellaneous System Information¶
-
os.
confstr
(name)¶ Return string-valued system configuration values. name specifies the configuration value to retrieve; it may be a string which is the name of a defined system value; these names are specified in a number of standards (POSIX, Unix 95, Unix 98, and others). Some platforms define additional names as well. The names known to the host operating system are given as the keys of the
confstr_names
dictionary. For configuration variables not included in that mapping, passing an integer for name is also accepted.If the configuration value specified by name isn’t defined,
None
is returned.If name is a string and is not known,
ValueError
is raised. If a specific value for name is not supported by the host system, even if it is included inconfstr_names
, anOSError
is raised witherrno.EINVAL
for the error number.Availability: Unix.
-
os.
confstr_names
¶ Dictionary mapping names accepted by
confstr()
to the integer values defined for those names by the host operating system. This can be used to determine the set of names known to the system.Availability: Unix.
-
os.
cpu_count
()¶ Return the number of CPUs in the system. Returns
None
if undetermined.This number is not equivalent to the number of CPUs the current process can use. The number of usable CPUs can be obtained with
len(os.sched_getaffinity(0))
New in version 3.4.
-
os.
getloadavg
()¶ Return the number of processes in the system run queue averaged over the last 1, 5, and 15 minutes or raises
OSError
if the load average was unobtainable.Availability: Unix.
-
os.
sysconf
(name)¶ Return integer-valued system configuration values. If the configuration value specified by name isn’t defined,
-1
is returned. The comments regarding the name parameter forconfstr()
apply here as well; the dictionary that provides information on the known names is given bysysconf_names
.Availability: Unix.
-
os.
sysconf_names
¶ Dictionary mapping names accepted by
sysconf()
to the integer values defined for those names by the host operating system. This can be used to determine the set of names known to the system.Availability: Unix.
The following data values are used to support path manipulation operations. These are defined for all platforms.
Higher-level operations on pathnames are defined in the os.path
module.
-
os.
curdir
¶ The constant string used by the operating system to refer to the current directory. This is
'.'
for Windows and POSIX. Also available viaos.path
.
-
os.
pardir
¶ The constant string used by the operating system to refer to the parent directory. This is
'..'
for Windows and POSIX. Also available viaos.path
.
-
os.
sep
¶ The character used by the operating system to separate pathname components. This is
'/'
for POSIX and'\\'
for Windows. Note that knowing this is not sufficient to be able to parse or concatenate pathnames — useos.path.split()
andos.path.join()
— but it is occasionally useful. Also available viaos.path
.
-
os.
altsep
¶ An alternative character used by the operating system to separate pathname components, or
None
if only one separator character exists. This is set to'/'
on Windows systems wheresep
is a backslash. Also available viaos.path
.
-
os.
extsep
¶ The character which separates the base filename from the extension; for example, the
'.'
inos.py
. Also available viaos.path
.
-
os.
pathsep
¶ The character conventionally used by the operating system to separate search path components (as in
PATH
), such as':'
for POSIX or';'
for Windows. Also available viaos.path
.
-
os.
defpath
¶ The default search path used by
exec*p*
andspawn*p*
if the environment doesn’t have a'PATH'
key. Also available viaos.path
.
-
os.
linesep
¶ The string used to separate (or, rather, terminate) lines on the current platform. This may be a single character, such as
'\n'
for POSIX, or multiple characters, for example,'\r\n'
for Windows. Do not use os.linesep as a line terminator when writing files opened in text mode (the default); use a single'\n'
instead, on all platforms.
-
os.
devnull
¶ The file path of the null device. For example:
'/dev/null'
for POSIX,'nul'
for Windows. Also available viaos.path
.
-
os.
RTLD_LAZY
¶ -
os.
RTLD_NOW
¶ -
os.
RTLD_GLOBAL
¶ -
os.
RTLD_LOCAL
¶ -
os.
RTLD_NODELETE
¶ -
os.
RTLD_NOLOAD
¶ -
os.
RTLD_DEEPBIND
¶ Flags for use with the
setdlopenflags()
andgetdlopenflags()
functions. See the Unix manual page dlopen(3) for what the different flags mean.New in version 3.3.
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
andGRND_NONBLOCK
.See also the Linux getrandom() manual page.
Availability: Linux 3.17 and newer.
New in version 3.6.
-
os.
urandom
(size)¶ Return a string of size random bytes suitable for cryptographic use.
This function returns random bytes from an OS-specific randomness source. The returned data should be unpredictable enough for cryptographic applications, though its exact quality depends on the OS implementation.
On Linux, if the
getrandom()
syscall is available, it is used in blocking mode: block until the system urandom entropy pool is initialized (128 bits of entropy are collected by the kernel). See the PEP 524 for the rationale. On Linux, thegetrandom()
function can be used to get random bytes in non-blocking mode (using theGRND_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, theNotImplementedError
exception is raised.On Windows, it will use
CryptGenRandom()
.See also
The
secrets
module provides higher level functions. For an easy-to-use interface to the random number generator provided by your platform, please seerandom.SystemRandom
.Changed in version 3.6.0: On Linux,
getrandom()
is now used in blocking mode to increase the security.Changed in version 3.5.2: On Linux, if the
getrandom()
syscall blocks (the urandom entropy pool is not initialized yet), fall back on reading/dev/urandom
.Changed in version 3.5: On Linux 3.17 and newer, the
getrandom()
syscall is now used when available. On OpenBSD 5.6 and newer, the Cgetentropy()
function is now used. These functions avoid the usage of an internal file descriptor.
-
os.
GRND_NONBLOCK
¶ By default, when reading from
/dev/random
,getrandom()
blocks if no random bytes are available, and when reading from/dev/urandom
, it blocks if the entropy pool has not yet been initialized.If the
GRND_NONBLOCK
flag is set, thengetrandom()
does not block in these cases, but instead immediately raisesBlockingIOError
.New in version 3.6.
-
os.
GRND_RANDOM
¶ If this bit is set, then random bytes are drawn from the
/dev/random
pool instead of the/dev/urandom
pool.New in version 3.6.