15.1. os — Miscellaneous operating system interfaces
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.
- An “Availability: Unix” note means that this function is commonly found on
Unix systems. It does not make any claims about its existence on a specific
operating system.
- If not separately noted, all functions that claim “Availability: Unix” are
supported on Mac OS X, which builds on a Unix core.
Note
All functions in this module raise OSError in the case of invalid or
inaccessible file names and paths, or other arguments that have the correct
type, but are not accepted by the operating system.
-
exception
os.error
An alias for the built-in OSError exception.
-
os.name
The name of the operating system dependent module imported. The following
names have currently been registered: 'posix', 'nt', 'mac',
'os2', 'ce', 'java', 'riscos'.
15.1.1. Process Parameters
These functions and data items provide information and operate on the current
process and user.
-
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 to getenv("HOME") in C.
This mapping is captured the first time the os module is imported,
typically during Python startup as part of processing site.py. Changes
to the environment made after this time are not reflected in os.environ,
except for changes made by modifying os.environ directly.
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.
Note
Calling putenv() directly does not change os.environ, so it’s better
to modify os.environ.
Note
On some platforms, including FreeBSD and Mac OS X, setting environ may
cause memory leaks. Refer to the system documentation for
:cfunc:`putenv`.
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 from os.environ, and when
one of the pop() or clear() methods is called.
Changed in version 2.6:
Changed in version 2.6: Also unset environment variables when calling os.environ.clear()
and os.environ.pop().
-
os.chdir(path)
-
os.fchdir(fd)
-
os.getcwd()
These functions are described in Files and Directories.
-
os.ctermid()
Return the filename corresponding to the controlling terminal of the process.
Availability: Unix.
-
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.getgroups()
Return list of supplemental group ids associated with the current process.
Availability: Unix.
-
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 the environment variable
LOGNAME to find out who the user is, or
pwd.getpwuid(os.getuid())[0] to get the login name of the currently
effective user id.
Availability: Unix.
-
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.
New in version 2.3:
New in version 2.3.
-
os.getpgrp()
Return the id of the current process group.
Availability: Unix.
-
os.getpid()
Return the current process id.
Availability: Unix, Windows.
-
os.getppid()
Return the parent’s process id.
Availability: Unix.
-
os.getuid()
Return the current process’s user id.
Availability: Unix.
-
os.getenv(varname[, value])
Return the value of the environment variable varname if it exists, or value
if it doesn’t. value defaults to None.
Availability: most flavors of Unix, Windows.
-
os.putenv(varname, value)
Set the environment variable named varname to the string value. Such
changes to the environment affect subprocesses started with os.system(),
popen() or fork() and execv().
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 in os.environ are
automatically translated into corresponding calls to putenv(); however,
calls to putenv() don’t update os.environ, so it is actually
preferable to assign to items of os.environ.
-
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.
New in version 2.2:
New in version 2.2.
-
os.setpgrp()
Call the system call :cfunc:`setpgrp` or :cfunc:`setpgrp(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 :cfunc:`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.setreuid(ruid, euid)
Set the current process’s real and effective user ids.
Availability: Unix.
-
os.setregid(rgid, egid)
Set the current process’s real and effective group ids.
Availability: Unix.
-
os.getsid(pid)
Call the system call :cfunc:`getsid`. See the Unix manual for the semantics.
Availability: Unix.
New in version 2.4:
New in version 2.4.
-
os.setsid()
Call the system call :cfunc:`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 :cfunc:`strerror` returns NULL when given an unknown
error number, ValueError is raised.
Availability: Unix, Windows.
-
os.umask(mask)
Set the current numeric umask and return the previous umask.
Availability: Unix, Windows.
-
os.uname()
Return a 5-tuple containing information identifying the current operating
system. The tuple contains 5 strings: (sysname, nodename, release, version,
machine). Some systems truncate the nodename to 8 characters or to the
leading component; a better way to get the hostname is
socket.gethostname() or even
socket.gethostbyaddr(socket.gethostname()).
Availability: recent flavors of Unix.
-
os.unsetenv(varname)
Unset (delete) the environment variable named varname. Such changes to the
environment affect subprocesses started with os.system(), popen() or
fork() and execv().
When unsetenv() is supported, deletion of items in os.environ is
automatically translated into a corresponding call to unsetenv(); however,
calls to unsetenv() don’t update os.environ, so it is actually
preferable to delete items of os.environ.
Availability: most flavors of Unix, Windows.
15.1.2. File Object Creation
These functions create new file objects. (See also open().)
-
os.fdopen(fd[, mode[, bufsize]])
Return an open file object connected to the file descriptor fd. The mode
and bufsize arguments have the same meaning as the corresponding arguments to
the built-in open() function.
Availability: Unix, Windows.
Changed in version 2.3:
Changed in version 2.3: When specified, the mode argument must now start with one of the letters
'r', 'w', or 'a', otherwise a ValueError is raised.
Changed in version 2.5:
Changed in version 2.5: On Unix, when the mode argument starts with 'a', the O_APPEND flag is
set on the file descriptor (which the :cfunc:`fdopen` implementation already
does on most platforms).
-
os.popen(command[, mode[, bufsize]])
Open a pipe to or from command. 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 bufsize argument has the same meaning as
the corresponding argument to the built-in open() function. The exit
status of the command (encoded in the format specified for wait()) is
available as the return value of the close() method of the file object,
except that when the exit status is zero (termination without errors), None
is returned.
Availability: Unix, Windows.
Deprecated since version 2.6:
Deprecated since version 2.6: This function is obsolete. Use the subprocess module. Check
especially the Replacing Older Functions with the subprocess Module section.
Changed in version 2.0:
Changed in version 2.0: This function worked unreliably under Windows in earlier versions of Python.
This was due to the use of the :cfunc:`_popen` function from the libraries
provided with Windows. Newer versions of Python do not use the broken
implementation from the Windows libraries.
-
os.tmpfile()
Return a new file object opened in update mode (w+b). The file has no
directory entries associated with it and will be automatically deleted once
there are no file descriptors for the file.
Availability: Unix, Windows.
There are a number of different popen*() functions that provide slightly
different ways to create subprocesses.
Deprecated since version 2.6:
Deprecated since version 2.6: All of the popen*() functions are obsolete. Use the subprocess
module.
For each of the popen*() variants, if bufsize is specified, it
specifies the buffer size for the I/O pipes. mode, if provided, should be the
string 'b' or 't'; on Windows this is needed to determine whether the
file objects should be opened in binary or text mode. The default value for
mode is 't'.
Also, for each of these variants, on Unix, cmd may be a sequence, in which
case arguments will be passed directly to the program without shell intervention
(as with os.spawnv()). If cmd is a string it will be passed to the shell
(as with os.system()).
These methods do not make it possible to retrieve the exit status from the child
processes. The only way to control the input and output streams and also
retrieve the return codes is to use the subprocess module; these are only
available on Unix.
For a discussion of possible deadlock conditions related to the use of these
functions, see Flow Control Issues.
-
os.popen2(cmd[, mode[, bufsize]])
Execute cmd as a sub-process and return the file objects (child_stdin,
child_stdout).
Deprecated since version 2.6:
Deprecated since version 2.6: This function is obsolete. Use the subprocess module. Check
especially the Replacing Older Functions with the subprocess Module section.
Availability: Unix, Windows.
New in version 2.0:
New in version 2.0.
-
os.popen3(cmd[, mode[, bufsize]])
Execute cmd as a sub-process and return the file objects (child_stdin,
child_stdout, child_stderr).
Deprecated since version 2.6:
Deprecated since version 2.6: This function is obsolete. Use the subprocess module. Check
especially the Replacing Older Functions with the subprocess Module section.
Availability: Unix, Windows.
New in version 2.0:
New in version 2.0.
-
os.popen4(cmd[, mode[, bufsize]])
Execute cmd as a sub-process and return the file objects (child_stdin,
child_stdout_and_stderr).
Deprecated since version 2.6:
Deprecated since version 2.6: This function is obsolete. Use the subprocess module. Check
especially the Replacing Older Functions with the subprocess Module section.
Availability: Unix, Windows.
New in version 2.0:
New in version 2.0.
(Note that child_stdin, child_stdout, and child_stderr are named from the
point of view of the child process, so child_stdin is the child’s standard
input.)
This functionality is also available in the popen2 module using functions
of the same names, but the return values of those functions have a different
order.
15.1.3. 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.
Availability: Unix, Windows.
Note
This function is intended for low-level I/O and must be applied to a file
descriptor as returned by os.open() or pipe(). To close a “file
object” returned by the built-in function open() or by popen() or
fdopen(), use its close() method.
-
os.closerange(fd_low, fd_high)
Close all file descriptors from fd_low (inclusive) to fd_high (exclusive),
ignoring errors. Equivalent to:
for fd in xrange(fd_low, fd_high):
try:
os.close(fd)
except OSError:
pass
Availability: Unix, Windows.
New in version 2.6:
New in version 2.6.
-
os.dup(fd)
Return a duplicate of file descriptor fd.
Availability: Unix, Windows.
-
os.dup2(fd, fd2)
Duplicate file descriptor fd to fd2, closing the latter first if necessary.
Availability: Unix, Windows.
-
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.
Availability: Unix.
New in version 2.6:
New in version 2.6.
-
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.
Availability: Unix.
New in version 2.6:
New in version 2.6.
-
os.fdatasync(fd)
Force write of file with filedescriptor fd to disk. Does not force update of
metadata.
Availability: Unix.
Note
This function is not available on MacOS.
-
os.fpathconf(fd, name)
Return system configuration information relevant to an open file. name
specifies the configuration value to retrieve; it may be a string which is the
name of a defined system value; these names are specified in a number of
standards (POSIX.1, Unix 95, Unix 98, and others). Some platforms define
additional names as well. The names known to the host operating system are
given in the pathconf_names dictionary. For configuration variables not
included in that mapping, passing an integer for name is also accepted.
If name is a string and is not known, ValueError is raised. If a
specific value for name is not supported by the host system, even if it is
included in pathconf_names, an OSError is raised with
errno.EINVAL for the error number.
Availability: Unix.
-
os.fstat(fd)
Return status for file descriptor fd, like stat().
Availability: Unix, Windows.
-
os.fstatvfs(fd)
Return information about the filesystem containing the file associated with file
descriptor fd, like statvfs().
Availability: Unix.
-
os.fsync(fd)
Force write of file with filedescriptor fd to disk. On Unix, this calls the
native :cfunc:`fsync` function; on Windows, the MS :cfunc:`_commit` function.
If you’re starting with a Python file object f, first do f.flush(), and
then do os.fsync(f.fileno()), to ensure that all internal buffers associated
with f are written to disk.
Availability: Unix, and Windows starting in 2.2.3.
-
os.ftruncate(fd, length)
Truncate the file corresponding to file descriptor fd, so that it is at most
length bytes in size.
Availability: Unix.
-
os.isatty(fd)
Return True if the file descriptor fd is open and connected to a
tty(-like) device, else False.
Availability: Unix.
-
os.lseek(fd, pos, how)
Set the current position of file descriptor fd to position pos, modified
by how: SEEK_SET or 0 to set the position relative to the
beginning of the file; SEEK_CUR or 1 to set it relative to the
current position; os.SEEK_END or 2 to set it relative to the end of
the file.
Availability: Unix, Windows.
-
os.SEEK_SET
-
os.SEEK_CUR
-
os.SEEK_END
Parameters to the lseek() function. Their values are 0, 1, and 2,
respectively. Availability: Windows, Unix.
New in version 2.5:
New in version 2.5.
-
os.open(file, flags[, mode])
Open the file file and set various flags according to flags and possibly its
mode according to mode. The default mode is 0777 (octal), and the
current umask value is first masked out. Return the file descriptor for the
newly opened file.
For a description of the flag and mode values, see the C run-time documentation;
flag constants (like O_RDONLY and O_WRONLY) are defined in
this module too (see open() flag constants). In particular, on Windows adding
O_BINARY is needed to open files in binary mode.
Availability: Unix, Windows.
Note
This function is intended for low-level I/O. For normal usage, use the
built-in function open(), which returns a “file object” with
read() and write() methods (and many more). To
wrap a file descriptor in a “file object”, use fdopen().
-
os.openpty()
Open a new pseudo-terminal pair. Return a pair of file descriptors (master,
slave) for the pty and the tty, respectively. For a (slightly) more portable
approach, use the pty module.
Availability: some flavors of Unix.
-
os.pipe()
Create a pipe. Return a pair of file descriptors (r, w) usable for reading
and writing, respectively.
Availability: Unix, Windows.
-
os.read(fd, n)
Read at most n bytes from file descriptor fd. Return a string containing the
bytes read. If the end of the file referred to by fd has been reached, an
empty string is returned.
Availability: Unix, Windows.
-
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 string str to file descriptor fd. Return the number of bytes
actually written.
Availability: Unix, Windows.
15.1.3.1. open() flag constants
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
These 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_SHLOCK
-
os.O_EXLOCK
These constants are only available on Unix.
-
os.O_BINARY
-
os.O_NOINHERIT
-
os.O_SHORT_LIVED
-
os.O_TEMPORARY
-
os.O_RANDOM
-
os.O_SEQUENTIAL
-
os.O_TEXT
These constants are only available on Windows.
-
os.O_ASYNC
-
os.O_DIRECT
-
os.O_DIRECTORY
-
os.O_NOFOLLOW
-
os.O_NOATIME
These constants are GNU extensions and not present if they are not defined by
the C library.
15.1.4. Files and Directories
-
os.access(path, mode)
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 of R_OK, W_OK, and
X_OK to test permissions. Return True if access is allowed,
False if not. See the Unix man page access(2) for more
information.
Availability: Unix, Windows.
Note
Using access() to check if a user is authorized to e.g. open a file
before actually doing so using open() creates a security hole,
because the user might exploit the short time interval between checking
and opening the file to manipulate it.
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.
-
os.F_OK
Value to pass as the mode parameter of access() to test the existence of
path.
-
os.R_OK
Value to include in the mode parameter of access() to test the
readability of path.
-
os.W_OK
Value to include in the mode parameter of access() to test the
writability of path.
-
os.X_OK
Value to include in the mode parameter of access() to determine if
path can be executed.
-
os.chdir(path)
Change the current working directory to path.
Availability: Unix, Windows.
-
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.
Availability: Unix.
New in version 2.3:
New in version 2.3.
-
os.getcwd()
Return a string representing the current working directory.
Availability: Unix, Windows.
-
os.getcwdu()
Return a Unicode object representing the current working directory.
Availability: Unix, Windows.
New in version 2.3:
New in version 2.3.
-
os.chflags(path, flags)
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):
UF_NODUMPUF_IMMUTABLEUF_APPENDUF_OPAQUEUF_NOUNLINKSF_ARCHIVEDSF_IMMUTABLESF_APPENDSF_NOUNLINKSF_SNAPSHOT
Availability: Unix.
New in version 2.6:
New in version 2.6.
-
os.chroot(path)
Change the root directory of the current process to path. Availability:
Unix.
New in version 2.2:
New in version 2.2.
-
os.chmod(path, mode)
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:
Availability: Unix, Windows.
Note
Although Windows supports chmod(), you can only set the file’s read-only
flag with it (via the stat.S_IWRITE and stat.S_IREAD
constants or a corresponding integer value). All other bits are
ignored.
-
os.chown(path, uid, gid)
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.
Availability: Unix.
-
os.lchflags(path, flags)
Set the flags of path to the numeric flags, like chflags(), but do not
follow symbolic links.
Availability: Unix.
New in version 2.6:
New in version 2.6.
-
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.
Availability: Unix.
New in version 2.6:
New in version 2.6.
-
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.
Availability: Unix.
New in version 2.3:
New in version 2.3.
-
os.link(source, link_name)
Create a hard link pointing to source named link_name.
Availability: Unix.
-
os.listdir(path)
Return a list containing the names of the entries in the directory given by
path. The list is in arbitrary order. It does not include the special
entries '.' and '..' even if they are present in the
directory.
Availability: Unix, Windows.
Changed in version 2.3:
Changed in version 2.3: On Windows NT/2k/XP and Unix, if path is a Unicode object, the result will be
a list of Unicode objects. Undecodable filenames will still be returned as
string objects.
-
os.lstat(path)
Like stat(), but do not follow symbolic links. This is an alias for
stat() on platforms that do not support symbolic links, such as
Windows.
-
os.mkfifo(path[, mode])
Create a FIFO (a named pipe) named path with numeric mode mode. The default
mode is 0666 (octal). The current umask value is first masked out from
the mode.
Availability: Unix.
FIFOs are pipes that can be accessed like regular files. FIFOs exist until they
are deleted (for example with os.unlink()). Generally, FIFOs are used as
rendezvous between “client” and “server” type processes: the server opens the
FIFO for reading, and the client opens it for writing. Note that mkfifo()
doesn’t open the FIFO — it just creates the rendezvous point.
-
os.mknod(filename[, mode=0600, device])
Create a filesystem node (file, device special file or named pipe) named
filename. mode specifies both the permissions to use and the type of node to
be created, being combined (bitwise OR) with one of stat.S_IFREG,
stat.S_IFCHR, stat.S_IFBLK,
and stat.S_IFIFO (those constants are available in stat).
For stat.S_IFCHR and
stat.S_IFBLK, device defines the newly created device special file (probably using
os.makedev()), otherwise it is ignored.
New in version 2.3:
New in version 2.3.
-
os.major(device)
Extract the device major number from a raw device number (usually the
st_dev or st_rdev field from :ctype:`stat`).
New in version 2.3:
New in version 2.3.
-
os.minor(device)
Extract the device minor number from a raw device number (usually the
st_dev or st_rdev field from :ctype:`stat`).
New in version 2.3:
New in version 2.3.
-
os.makedev(major, minor)
Compose a raw device number from the major and minor device numbers.
New in version 2.3:
New in version 2.3.
-
os.mkdir(path[, mode])
Create a directory named path with numeric mode mode. The default mode is
0777 (octal). On some systems, mode is ignored. Where it is used, the
current umask value is first masked out.
It is also possible to create temporary directories; see the
tempfile module’s tempfile.mkdtemp() function.
Availability: Unix, Windows.
-
os.makedirs(path[, mode])
Recursive directory creation function. Like mkdir(), but makes all
intermediate-level directories needed to contain the leaf directory. Throws an
error exception if the leaf directory already exists or cannot be
created. The default mode is 0777 (octal). On some systems, mode is
ignored. Where it is used, the current umask value is first masked out.
New in version 1.5.2:
New in version 1.5.2.
Changed in version 2.3:
Changed in version 2.3: This function now handles UNC paths correctly.
-
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 in pathconf_names, an OSError is raised with
errno.EINVAL for the error number.
Availability: Unix.
-
os.pathconf_names
Dictionary mapping names accepted by pathconf() and fpathconf() to
the integer values defined for those names by the host operating system. This
can be used to determine the set of names known to the system. Availability:
Unix.
-
os.readlink(path)
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).
Changed in version 2.6:
Changed in version 2.6: If the path is a Unicode object the result will also be a Unicode object.
Availability: Unix.
-
os.remove(path)
Remove (delete) the file path. If path is a directory, OSError is
raised; see rmdir() below to remove a directory. This is identical to
the unlink() function documented below. 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.
Availability: Unix, Windows.
-
os.removedirs(path)
Remove directories recursively. Works like rmdir() except that, if the
leaf directory is successfully removed, removedirs() tries to
successively remove every parent directory mentioned in path until an error
is raised (which is ignored, because it generally means that a parent directory
is not empty). For example, os.removedirs('foo/bar/baz') will first remove
the directory 'foo/bar/baz', and then remove 'foo/bar' and 'foo' if
they are empty. Raises OSError if the leaf directory could not be
successfully removed.
New in version 1.5.2:
New in version 1.5.2.
-
os.rename(src, dst)
Rename the file or directory src to dst. If dst is a directory,
OSError will be raised. On Unix, if dst exists and is a file, it will
be replaced silently if the user has permission. The operation may fail on some
Unix flavors if src and dst are on different filesystems. If successful,
the renaming will be an atomic operation (this is a POSIX requirement). On
Windows, if dst already exists, OSError will be raised even if it is a
file; there may be no way to implement an atomic rename when dst names an
existing file.
Availability: Unix, Windows.
-
os.renames(old, new)
Recursive directory or file renaming function. Works like rename(), except
creation of any intermediate directories needed to make the new pathname good is
attempted first. After the rename, directories corresponding to rightmost path
segments of the old name will be pruned away using removedirs().
New in version 1.5.2:
New in version 1.5.2.
Note
This function can fail with the new directory structure made if you lack
permissions needed to remove the leaf directory or file.
-
os.rmdir(path)
Remove (delete) the directory path. Only works when the directory is
empty, otherwise, OSError is raised. In order to remove whole
directory trees, shutil.rmtree() can be used.
Availability: Unix, Windows.
-
os.stat(path)
Perform a :cfunc:`stat` system call on the given path. The return value is an
object whose attributes correspond to the members of the :ctype:`stat`
structure, namely: st_mode (protection bits), st_ino (inode
number), st_dev (device), st_nlink (number of hard links),
st_uid (user id of owner), st_gid (group id of owner),
st_size (size of file, in bytes), st_atime (time of most recent
access), st_mtime (time of most recent content modification),
st_ctime (platform dependent; time of most recent metadata change on
Unix, or the time of creation on Windows):
>>> import os
>>> statinfo = os.stat('somefile.txt')
>>> statinfo
(33188, 422511L, 769L, 1, 1032, 100, 926L, 1105022698,1105022732, 1105022732)
>>> statinfo.st_size
926L
>>>
Changed in version 2.3:
Changed in version 2.3: If stat_float_times() returns True, the time values are floats, measuring
seconds. Fractions of a second may be reported if the system supports that. On
Mac OS, the times are always floats. See stat_float_times() for further
discussion.
On some Unix systems (such as Linux), the following attributes may also be
available: st_blocks (number of blocks allocated for file),
st_blksize (filesystem blocksize), st_rdev (type of device if an
inode device). st_flags (user defined flags for file).
On other Unix systems (such as FreeBSD), the following attributes may be
available (but may be only filled out if root tries to use them): st_gen
(file generation number), st_birthtime (time of file creation).
On Mac OS systems, the following attributes may also be available:
st_rsize, st_creator, st_type.
On RISCOS systems, the following attributes are also available: st_ftype
(file type), st_attrs (attributes), st_obtype (object type).
For backward compatibility, the return value of stat() is also accessible
as a tuple of at least 10 integers giving the most important (and portable)
members of the :ctype:`stat` structure, in the order st_mode,
st_ino, st_dev, st_nlink, st_uid,
st_gid, st_size, st_atime, st_mtime,
st_ctime. More items may be added at the end by some implementations.
The standard module stat defines functions and constants that are useful
for extracting information from a :ctype:`stat` structure. (On Windows, some
items are filled with dummy values.)
Note
The exact meaning and resolution of the st_atime, st_mtime, and
st_ctime members depends on the operating system and the file system.
For example, on Windows systems using the FAT or FAT32 file systems,
st_mtime has 2-second resolution, and st_atime has only 1-day
resolution. See your operating system documentation for details.
Availability: Unix, Windows.
Changed in version 2.2:
Changed in version 2.2: Added access to values as attributes of the returned object.
Changed in version 2.5:
Changed in version 2.5: Added st_gen and st_birthtime.
-
os.stat_float_times([newvalue])
Determine whether stat_result represents time stamps as float objects.
If newvalue is True, future calls to stat() return floats, if it is
False, future calls return ints. If newvalue is omitted, return the
current setting.
For compatibility with older Python versions, accessing stat_result as
a tuple always returns integers.
Changed in version 2.5:
Changed in version 2.5: Python now returns float values by default. Applications which do not work
correctly with floating point time stamps can use this function to restore the
old behaviour.
The resolution of the timestamps (that is the smallest possible fraction)
depends on the system. Some systems only support second resolution; on these
systems, the fraction will always be zero.
It is recommended that this setting is only changed at program startup time in
the __main__ module; libraries should never change this setting. If an
application uses a library that works incorrectly if floating point time stamps
are processed, this application should turn the feature off until the library
has been corrected.
-
os.statvfs(path)
Perform a :cfunc:`statvfs` system call on the given path. The return value is
an object whose attributes describe the filesystem on the given path, and
correspond to the members of the :ctype:`statvfs` structure, namely:
f_bsize, f_frsize, f_blocks, f_bfree,
f_bavail, f_files, f_ffree, f_favail,
f_flag, f_namemax.
For backward compatibility, the return value is also accessible as a tuple whose
values correspond to the attributes, in the order given above. The standard
module statvfs defines constants that are useful for extracting
information from a :ctype:`statvfs` structure when accessing it as a sequence;
this remains useful when writing code that needs to work with versions of Python
that don’t support accessing the fields as attributes.
Availability: Unix.
Changed in version 2.2:
Changed in version 2.2: Added access to values as attributes of the returned object.
-
os.symlink(source, link_name)
Create a symbolic link pointing to source named link_name.
Availability: Unix.
-
os.tempnam([dir[, prefix]])
Return a unique path name that is reasonable for creating a temporary file.
This will be an absolute path that names a potential directory entry in the
directory dir or a common location for temporary files if dir is omitted or
None. If given and not None, prefix is used to provide a short prefix
to the filename. Applications are responsible for properly creating and
managing files created using paths returned by tempnam(); no automatic
cleanup is provided. On Unix, the environment variable TMPDIR
overrides dir, while on Windows TMP is used. The specific
behavior of this function depends on the C library implementation; some aspects
are underspecified in system documentation.
Availability: Unix, Windows.
-
os.tmpnam()
Return a unique path name that is reasonable for creating a temporary file.
This will be an absolute path that names a potential directory entry in a common
location for temporary files. Applications are responsible for properly
creating and managing files created using paths returned by tmpnam(); no
automatic cleanup is provided.
Availability: Unix, Windows. This function probably shouldn’t be used on
Windows, though: Microsoft’s implementation of tmpnam() always creates a
name in the root directory of the current drive, and that’s generally a poor
location for a temp file (depending on privileges, you may not even be able to
open a file using this name).
-
os.TMP_MAX
The maximum number of unique names that tmpnam() will generate before
reusing names.
-
os.unlink(path)
Remove (delete) the file path. This is the same function as
remove(); the unlink() name is its traditional Unix
name.
Availability: Unix, Windows.
-
os.utime(path, times)
Set the access and modified times of the file specified by path. If times
is None, then the file’s access and modified times are set to the current
time. (The effect is similar to running the Unix program touch on
the path.) Otherwise, times must be a 2-tuple of numbers, of the form
(atime, mtime) which is used to set the access and modified times,
respectively. Whether a directory can be given for path depends on whether
the operating system implements directories as files (for example, Windows
does not). Note that the exact times you set here may not be returned by a
subsequent stat() call, depending on the resolution with which your
operating system records access and modification times; see stat().
Changed in version 2.0:
Changed in version 2.0: Added support for None for times.
Availability: Unix, Windows.
-
os.walk(top[, topdown=True[, onerror=None[, followlinks=False]]])
Generate the file names in a directory tree by walking the tree
either top-down or bottom-up. For each directory in the tree rooted at directory
top (including top itself), it yields a 3-tuple (dirpath, dirnames,
filenames).
dirpath is a string, the path to the directory. dirnames is a list of the
names of the subdirectories in dirpath (excluding '.' and '..').
filenames is a list of the names of the non-directory files in dirpath.
Note that the names in the lists contain no path components. To get a full path
(which begins with top) to a file or directory in dirpath, do
os.path.join(dirpath, name).
If optional argument topdown is True or not specified, the triple for a
directory is generated before the triples for any of its subdirectories
(directories are generated top-down). If topdown is False, the triple for a
directory is generated after the triples for all of its subdirectories
(directories are generated bottom-up).
When topdown is True, the caller can modify the dirnames list in-place
(perhaps using del or slice assignment), and walk() will only
recurse into the subdirectories whose names remain in dirnames; this can be
used to prune the search, impose a specific order of visiting, or even to inform
walk() about directories the caller creates or renames before it resumes
walk() again. Modifying dirnames when topdown is False is
ineffective, because in bottom-up mode the directories in dirnames are
generated before dirpath itself is generated.
By default errors from the listdir() call are ignored. If optional
argument onerror is specified, it should be a function; it will be called with
one argument, an OSError instance. It can report the error to continue
with the walk, or raise the exception to abort the walk. Note that the filename
is available as the filename attribute of the exception object.
By default, walk() will not walk down into symbolic links that resolve to
directories. Set followlinks to True to visit directories pointed to by
symlinks, on systems that support them.
New in version 2.6:
New in version 2.6: The followlinks parameter.
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",
print sum(getsize(join(root, name)) for name in files),
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 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))
New in version 2.3:
New in version 2.3.
15.1.5. 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 :cfunc:`main`. For example, os.execv('/bin/echo',
['foo', 'bar']) will only print bar on standard output; foo will seem
to be ignored.
-
os.abort()
Generate a SIGABRT signal to the current process. On Unix, the default
behavior is to produce a core dump; on Windows, the process immediately returns
an exit code of 3. Be aware that programs which use signal.signal()
to register a handler for SIGABRT will behave differently.
Availability: Unix, Windows.
-
os.execl(path, arg0, arg1, ...)
-
os.execle(path, arg0, arg1, ..., env)
-
os.execlp(file, arg0, arg1, ...)
-
os.execlpe(file, arg0, arg1, ..., env)
-
os.execv(path, args)
-
os.execve(path, args, env)
-
os.execvp(file, args)
-
os.execvpe(file, args, env)
These functions all execute a new program, replacing the current process; they
do not return. On Unix, the new executable is loaded into the current process,
and will have the same process id as the caller. Errors will be reported as
OSError exceptions.
The current process is replaced immediately. Open file objects and
descriptors are not flushed, so if there may be data buffered
on these open files, you should flush them using
sys.stdout.flush() or os.fsync() before calling an
exec*() function.
The “l” and “v” variants of the exec*() functions differ in how
command-line arguments are passed. The “l” variants are perhaps the easiest
to work with if the number of parameters is fixed when the code is written; the
individual parameters simply become additional parameters to the execl*()
functions. The “v” variants are good when the number of parameters is
variable, with the arguments being passed in a list or tuple as the args
parameter. In either case, the arguments to the child process should start with
the name of the command being run, but this is not enforced.
The variants which include a “p” near the end (execlp(),
execlpe(), execvp(), and execvpe()) will use the
PATH environment variable to locate the program file. When the
environment is being replaced (using one of the exec*e() variants,
discussed in the next paragraph), the new environment is used as the source of
the PATH variable. The other variants, execl(), execle(),
execv(), and execve(), will not use the PATH variable to
locate the executable; path must contain an appropriate absolute or relative
path.
For execle(), execlpe(), execve(), and execvpe() (note
that these all end in “e”), the env parameter must be a mapping which is
used to define the environment variables for the new process (these are used
instead of the current process’ environment); the functions execl(),
execlp(), execv(), and execvp() all cause the new process to
inherit the environment of the current process.
Availability: Unix, Windows.
-
os._exit(n)
Exit to the system with status n, without calling cleanup handlers, flushing
stdio buffers, etc.
Availability: Unix, Windows.
Note
The standard way to exit is sys.exit(n). _exit() should normally only
be used in the child process after a fork().
The following exit codes are defined and can be used with _exit(),
although they are not required. These are typically used for system programs
written in Python, such as a mail server’s external command delivery program.
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.
New in version 2.3:
New in version 2.3.
-
os.EX_USAGE
Exit code that means the command was used incorrectly, such as when the wrong
number of arguments are given.
Availability: Unix.
New in version 2.3:
New in version 2.3.
-
os.EX_DATAERR
Exit code that means the input data was incorrect.
Availability: Unix.
New in version 2.3:
New in version 2.3.
-
os.EX_NOINPUT
Exit code that means an input file did not exist or was not readable.
Availability: Unix.
New in version 2.3:
New in version 2.3.
-
os.EX_NOUSER
Exit code that means a specified user did not exist.
Availability: Unix.
New in version 2.3:
New in version 2.3.
-
os.EX_NOHOST
Exit code that means a specified host did not exist.
Availability: Unix.
New in version 2.3:
New in version 2.3.
-
os.EX_UNAVAILABLE
Exit code that means that a required service is unavailable.
Availability: Unix.
New in version 2.3:
New in version 2.3.
-
os.EX_SOFTWARE
Exit code that means an internal software error was detected.
Availability: Unix.
New in version 2.3:
New in version 2.3.
-
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.
New in version 2.3:
New in version 2.3.
-
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.
New in version 2.3:
New in version 2.3.
-
os.EX_CANTCREAT
Exit code that means a user specified output file could not be created.
Availability: Unix.
New in version 2.3:
New in version 2.3.
-
os.EX_IOERR
Exit code that means that an error occurred while doing I/O on some file.
Availability: Unix.
New in version 2.3:
New in version 2.3.
-
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.
New in version 2.3:
New in version 2.3.
-
os.EX_PROTOCOL
Exit code that means that a protocol exchange was illegal, invalid, or not
understood.
Availability: Unix.
New in version 2.3:
New in version 2.3.
-
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.
New in version 2.3:
New in version 2.3.
-
os.EX_CONFIG
Exit code that means that some kind of configuration error occurred.
Availability: Unix.
New in version 2.3:
New in version 2.3.
-
os.EX_NOTFOUND
Exit code that means something like “an entry was not found”.
Availability: Unix.
New in version 2.3:
New in version 2.3.
-
os.fork()
Fork a child process. Return 0 in the child and the child’s process id in the
parent. If an error occurs OSError is raised.
Note that some platforms including FreeBSD <= 6.3, Cygwin and OS/2 EMX have
known issues when using fork() from a thread.
Availability: Unix.
-
os.forkpty()
Fork a child process, using a new pseudo-terminal as the child’s controlling
terminal. Return a pair of (pid, fd), where pid is 0 in the child, the
new child’s process id in the parent, and fd is the file descriptor of the
master end of the pseudo-terminal. For a more portable approach, use the
pty module. If an error occurs OSError is raised.
Availability: some flavors of Unix.
-
os.kill(pid, sig)
Send signal sig to the process pid. Constants for the specific signals
available on the host platform are defined in the signal module.
Availability: Unix.
-
os.killpg(pgid, sig)
Send the signal sig to the process group pgid.
Availability: Unix.
New in version 2.3:
New in version 2.3.
-
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(...)
-
os.popen2(...)
-
os.popen3(...)
-
os.popen4(...)
Run child processes, returning opened pipes for communications. These functions
are described in section File Object Creation.
-
os.spawnl(mode, path, ...)
-
os.spawnle(mode, path, ..., env)
-
os.spawnlp(mode, file, ...)
-
os.spawnlpe(mode, file, ..., env)
-
os.spawnv(mode, path, args)
-
os.spawnve(mode, path, args, env)
-
os.spawnvp(mode, file, args)
-
os.spawnvpe(mode, file, args, env)
Execute the program path in a new process.
(Note that the subprocess module provides more powerful facilities for
spawning new processes and retrieving their results; using that module is
preferable to using these functions. Check especially the
Replacing Older Functions with the subprocess Module section.)
If mode is P_NOWAIT, this function returns the process id of the new
process; if mode is P_WAIT, returns the process’s exit code if it
exits normally, or -signal, where signal is the signal that killed the
process. On Windows, the process id will actually be the process handle, so can
be used with the waitpid() function.
The “l” and “v” variants of the spawn*() functions differ in how
command-line arguments are passed. The “l” variants are perhaps the easiest
to work with if the number of parameters is fixed when the code is written; the
individual parameters simply become additional parameters to the
spawnl*() functions. The “v” variants are good when the number of
parameters is variable, with the arguments being passed in a list or tuple as
the args parameter. In either case, the arguments to the child process must
start with the name of the command being run.
The variants which include a second “p” near the end (spawnlp(),
spawnlpe(), spawnvp(), and spawnvpe()) will use the
PATH environment variable to locate the program file. When the
environment is being replaced (using one of the spawn*e() variants,
discussed in the next paragraph), the new environment is used as the source of
the PATH variable. The other variants, spawnl(),
spawnle(), spawnv(), and spawnve(), will not use the
PATH variable to locate the executable; path must contain an
appropriate absolute or relative path.
For spawnle(), spawnlpe(), spawnve(), and spawnvpe()
(note that these all end in “e”), the env parameter must be a mapping
which is used to define the environment variables for the new process (they are
used instead of the current process’ environment); the functions
spawnl(), spawnlp(), spawnv(), and spawnvp() all cause
the new process to inherit the environment of the current process. Note that
keys and values in the env dictionary must be strings; invalid keys or
values will cause the function to fail, with a return value of 127.
As an example, the following calls to spawnlp() and spawnvpe() are
equivalent:
import os
os.spawnlp(os.P_WAIT, 'cp', 'cp', 'index.html', '/dev/null')
L = ['cp', 'index.html', '/dev/null']
os.spawnvpe(os.P_WAIT, 'cp', L, os.environ)
Availability: Unix, Windows. spawnlp(), spawnlpe(), spawnvp()
and spawnvpe() are not available on Windows.
New in version 1.6:
New in version 1.6.
-
os.P_NOWAIT
-
os.P_NOWAITO
Possible values for the mode parameter to the spawn*() family of
functions. If either of these values is given, the spawn*() functions
will return as soon as the new process has been created, with the process id as
the return value.
Availability: Unix, Windows.
New in version 1.6:
New in version 1.6.
-
os.P_WAIT
Possible value for the mode parameter to the spawn*() family of
functions. If this is given as mode, the spawn*() functions will not
return until the new process has run to completion and will return the exit code
of the process the run is successful, or -signal if a signal kills the
process.
Availability: Unix, Windows.
New in version 1.6:
New in version 1.6.
-
os.P_DETACH
-
os.P_OVERLAY
Possible values for the mode parameter to the spawn*() family of
functions. These are less portable than those listed above. P_DETACH
is similar to P_NOWAIT, but the new process is detached from the
console of the calling process. If P_OVERLAY is used, the current
process will be replaced; the spawn*() function will not return.
Availability: Windows.
New in version 1.6:
New in version 1.6.
-
os.startfile(path[, operation])
Start a file with its associated application.
When operation is not specified or 'open', this acts like double-clicking
the file in Windows Explorer, or giving the file name as an argument to the
start command from the interactive command shell: the file is opened
with whatever application (if any) its extension is associated.
When another operation is given, it must be a “command verb” that specifies
what should be done with the file. Common verbs documented by Microsoft are
'print' and 'edit' (to be used on files) as well as 'explore' and
'find' (to be used on directories).
startfile() returns as soon as the associated application is launched.
There is no option to wait for the application to close, and no way to retrieve
the application’s exit status. The path parameter is relative to the current
directory. If you want to use an absolute path, make sure the first character
is not a slash ('/'); the underlying Win32 :cfunc:`ShellExecute` function
doesn’t work if it is. Use the os.path.normpath() function to ensure that
the path is properly encoded for Win32.
Availability: Windows.
New in version 2.0:
New in version 2.0.
New in version 2.5:
New in version 2.5: The operation parameter.
-
os.system(command)
Execute the command (a string) in a subshell. This is implemented by calling
the Standard C function :cfunc:`system`, and has the same limitations.
Changes to sys.stdin, etc. are not reflected in the environment of the
executed command.
On Unix, the return value is the exit status of the process encoded in the
format specified for wait(). Note that POSIX does not specify the meaning
of the return value of the C :cfunc:`system` function, so the return value of
the Python function is system-dependent.
On Windows, the return value is that returned by the system shell after running
command, given by the Windows environment variable COMSPEC: on
command.com systems (Windows 95, 98 and ME) this is always 0; on
cmd.exe systems (Windows NT, 2000 and XP) this is the exit status of
the command run; on systems using a non-native shell, consult your shell
documentation.
The subprocess module provides more powerful facilities for spawning new
processes and retrieving their results; using that module is preferable to using
this function. See the
Replacing Older Functions with the subprocess Module section in the subprocess documentation
for some helpful recipes.
Availability: Unix, Windows.
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os.times()
Return a 5-tuple of floating point numbers indicating accumulated (processor
or other) times, in seconds. The items are: user time, system time,
children’s user time, children’s system time, and elapsed real time since a
fixed point in the past, in that order. See the Unix manual page
times(2) or the corresponding Windows Platform API documentation.
On Windows, only the first two items are filled, the others are zero.
Availability: Unix, Windows
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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.
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os.waitpid(pid, options)
The details of this function differ on Unix and Windows.
On Unix: Wait for completion of a child process given by process id pid, and
return a tuple containing its process id and exit status indication (encoded as
for wait()). The semantics of the call are affected by the value of the
integer options, which should be 0 for normal operation.
If pid is greater than 0, waitpid() requests status information for
that specific process. If pid is 0, the request is for the status of any
child in the process group of the current process. If pid is -1, the
request pertains to any child of the current process. If pid is less than
-1, status is requested for any process in the process group -pid (the
absolute value of pid).
An OSError is raised with the value of errno when the syscall
returns -1.
On Windows: Wait for completion of a process given by process handle pid, and
return a tuple containing pid, and its exit status shifted left by 8 bits
(shifting makes cross-platform use of the function easier). A pid less than or
equal to 0 has no special meaning on Windows, and raises an exception. The
value of integer options has no effect. pid can refer to any process whose
id is known, not necessarily a child process. The spawn() functions called
with P_NOWAIT return suitable process handles.
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os.wait3([options])
Similar to waitpid(), except no process id argument is given and a
3-element tuple containing the child’s process id, exit status indication, and
resource usage information is returned. Refer to resource.getrusage() for details on resource usage information. The option
argument is the same as that provided to waitpid() and wait4().
Availability: Unix.
New in version 2.5:
New in version 2.5.
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os.wait4(pid, options)
Similar to waitpid(), except a 3-element tuple, containing the child’s
process id, exit status indication, and resource usage information is returned.
Refer to resource.getrusage() for details on resource usage
information. The arguments to wait4() are the same as those provided to
waitpid().
Availability: Unix.
New in version 2.5:
New in version 2.5.
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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.
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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.
New in version 2.3:
New in version 2.3.
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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.
New in version 2.3:
New in version 2.3.
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.
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os.WCOREDUMP(status)
Return True if a core dump was generated for the process, otherwise
return False.
Availability: Unix.
New in version 2.3:
New in version 2.3.
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os.WIFCONTINUED(status)
Return True if the process has been continued from a job control stop,
otherwise return False.
Availability: Unix.
New in version 2.3:
New in version 2.3.
-
os.WIFSTOPPED(status)
Return True if the process has been stopped, otherwise return
False.
Availability: Unix.
-
os.WIFSIGNALED(status)
Return True if the process exited due to a signal, otherwise return
False.
Availability: Unix.
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os.WIFEXITED(status)
Return True if the process exited using the exit(2) system call,
otherwise return False.
Availability: Unix.
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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.
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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.
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os.sysconf(name)
Return integer-valued system configuration values. If the configuration value
specified by name isn’t defined, -1 is returned. The comments regarding
the name parameter for confstr() apply here as well; the dictionary that
provides information on the known names is given by sysconf_names.
Availability: Unix.
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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.
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os.curdir
The constant string used by the operating system to refer to the current
directory. This is '.' for Windows and POSIX. Also available via
os.path.
-
os.pardir
The constant string used by the operating system to refer to the parent
directory. This is '..' for Windows and POSIX. Also available via
os.path.
-
os.sep
The character used by the operating system to separate pathname components.
This is '/' for POSIX and '\\' for Windows. Note that knowing this
is not sufficient to be able to parse or concatenate pathnames — use
os.path.split() and os.path.join() — but it is occasionally
useful. Also available via os.path.
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os.altsep
An alternative character used by the operating system to separate pathname
components, or None if only one separator character exists. This is set to
'/' on Windows systems where sep is a backslash. Also available via
os.path.
-
os.extsep
The character which separates the base filename from the extension; for example,
the '.' in os.py. Also available via os.path.
New in version 2.2:
New in version 2.2.
-
os.pathsep
The character conventionally used by the operating system to separate search
path components (as in PATH), such as ':' for POSIX or ';' for
Windows. Also available via os.path.
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os.defpath
The default search path used by exec*p*() and spawn*p*() if the
environment doesn’t have a 'PATH' key. Also available via os.path.
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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.
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os.devnull
The file path of the null device. For example: '/dev/null' for
POSIX, 'nul' for Windows. Also available via os.path.
New in version 2.4:
New in version 2.4.
15.1.7. Miscellaneous Functions
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os.urandom(n)
Return a string of n 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 a UNIX-like
system this will query /dev/urandom, and on Windows it will use CryptGenRandom.
If a randomness source is not found, NotImplementedError will be raised.
New in version 2.4:
New in version 2.4.