15.1. os — Miscellaneous operating system interfaces¶

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 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: 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.

Note

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

os.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 2.7.

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 process’s real 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.

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.getresuid()¶

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

Availability: Unix.

New in version 2.7.

os.getresgid()¶

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

Availability: Unix.

New in version 2.7.

os.getuid()¶

Return the current process’s real 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.

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() or 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 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.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 2.7.

os.setresuid(ruid, euid, suid)¶

Set the current process’s real, effective, and saved user ids.

Availability: Unix.

New in version 2.7.

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.

New in version 2.4.

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() 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. If fdopen() raises an exception, it leaves fd untouched (unclosed).

Availability: Unix, Windows.

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: On Unix, when the mode argument starts with 'a', the O_APPEND flag is set on the file descriptor (which the 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: This function is obsolete. Use the subprocess module. Check especially the Replacing Older Functions with the subprocess Module section.

Changed in version 2.0: This function worked unreliably under Windows in earlier versions of Python. This was due to the use of the _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.

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: 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.

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: 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.

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: 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.

(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.

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.

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.

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 fsync() function; on Windows, the MS _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.

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; SEEK_END or 2 to set it relative to the end of the file. Return the new cursor position in bytes, starting from the beginning.

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.

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.

Note

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

os.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.

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 write a “file object” returned by the built-in function open() or by popen() or fdopen(), or sys.stdout or sys.stderr, use its write() method.

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. 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 IOError as e:
    if e.errno == errno.EACCES:
        return "some default data"
    # Not a permission error.
    raise
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.

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.

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.

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):

• stat.UF_NODUMP

• stat.UF_IMMUTABLE

• stat.UF_APPEND

• stat.UF_OPAQUE

• stat.UF_NOUNLINK

• stat.UF_COMPRESSED

• stat.UF_HIDDEN

• stat.SF_ARCHIVED

• stat.SF_IMMUTABLE

• stat.SF_APPEND

• stat.SF_NOUNLINK

• stat.SF_SNAPSHOT

Availability: Unix.

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.

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:

• stat.S_ISUID

• stat.S_ISGID

• stat.S_ENFMT

• stat.S_ISVTX

• stat.S_IREAD

• stat.S_IWRITE

• stat.S_IEXEC

• stat.S_IRWXU

• stat.S_IRUSR

• stat.S_IWUSR

• stat.S_IXUSR

• stat.S_IRWXG

• stat.S_IRGRP

• stat.S_IWGRP

• stat.S_IXGRP

• stat.S_IRWXO

• stat.S_IROTH

• stat.S_IWOTH

• stat.S_IXOTH

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.

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.

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.

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: 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)¶

Perform the equivalent of an lstat() system call on the given path. Similar to stat(), but does not follow symbolic links. On platforms that do not support symbolic links, this is an alias for stat().

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=0]])¶

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.

os.major(device)¶

Extract the device major number from a raw device number (usually the st_dev or st_rdev field from stat).

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 stat).

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.

os.mkdir(path[, mode])¶

Create a directory named path with numeric mode mode. The default mode is 0777 (octal). If the directory already exists, OSError 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.

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. Raises an error exception if the leaf directory already exists or cannot be created. The default mode is 0777 (octal).

The mode parameter is passed to mkdir(); see the mkdir() description for how it is interpreted.

Note

makedirs() will become confused if the path elements to create include os.pardir.

New in version 1.5.2.

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: 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.

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.

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 the equivalent of a stat() system call on the given path. (This function follows symlinks; to stat a symlink use lstat().)

The return value is an object whose attributes correspond to the members of the 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)

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. 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 512-byte blocks allocated for file

• st_blksize - filesystem blocksize for efficient file system I/O

• 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 RISCOS systems, the following attributes are also available:

• st_ftype (file type)

• st_attrs (attributes)

• st_obtype (object type).

Note

The exact meaning and resolution of the st_atime, st_mtime, and st_ctime attributes depend on the operating system and the file system. For example, on Windows systems using the FAT or FAT32 file systems, st_mtime has 2-second resolution, and st_atime has only 1-day resolution. See your operating system documentation for details.

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 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 stat structure. (On Windows, some items are filled with dummy values.)

Example:

>>> import os
>>> statinfo = os.stat('somefile.txt')
>>> statinfo
(33188, 422511, 769, 1, 1032, 100, 926, 1105022698,1105022732, 1105022732)
>>> statinfo.st_size
926

Availability: Unix, Windows.

Changed in version 2.2: Added access to values as attributes of the returned object.

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: 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 statvfs() system call on the given path. The return value is an object whose attributes describe the filesystem on the given path, and correspond to the members of the statvfs structure, namely: f_bsize, f_frsize, f_blocks, f_bfree, f_bavail, f_files, f_ffree, f_favail, f_flag, f_namemax.

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 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: 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.

Warning

Use of tempnam() is vulnerable to symlink attacks; consider using tmpfile() (section File Object Creation) instead.

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.

Warning

Use of tmpnam() is vulnerable to symlink attacks; consider using tmpfile() (section File Object Creation) instead.

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: Added support for None for times.

Availability: Unix, Windows.

os.walk(top, topdown=True, >, followlinks=False)¶

Generate the file names in a directory tree by walking the tree either top-down or bottom-up. For each directory in the tree rooted at directory top (including top itself), it yields a 3-tuple (dirpath, dirnames, filenames).

dirpath is a string, the path to the directory. dirnames is a list of the names of the subdirectories in dirpath (excluding '.' and '..'). filenames is a list of the names of the non-directory files in dirpath. Note that the names in the lists contain no path components. To get a full path (which begins with top) to a file or directory in dirpath, do os.path.join(dirpath, name).

If optional argument topdown is True or not specified, the triple for a directory is generated before the triples for any of its subdirectories (directories are generated top-down). If topdown is False, the triple for a directory is generated after the triples for all of its subdirectories (directories are generated bottom-up). No matter the value of topdown, the list of subdirectories is retrieved before the tuples for the directory and its subdirectories are generated.

When topdown is True, the caller can modify the dirnames list in-place (perhaps using del or slice assignment), and walk() will only recurse into the subdirectories whose names remain in dirnames; this can be used to prune the search, impose a specific order of visiting, or even to inform walk() about directories the caller creates or renames before it resumes walk() again. Modifying dirnames when topdown is False has no effect on the behavior of the walk, because in bottom-up mode the directories in dirnames are generated before dirpath itself is generated.

By default, errors from the 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: 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.