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.
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!
Note
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.
These functions and data items provide information and operate on the current process and user.
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().
Return the current process’s effective user id. Availability: Unix.
Return the real group id of the current process. Availability: Unix.
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.
Return the id of the current process group. Availability: Unix.
Return the current process id. Availability: Unix, Windows.
Return the parent’s process id. Availability: Unix.
Return the current process’s user id. Availability: Unix.
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.
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.
Call the system call getsid(). See the Unix manual for the semantics. Availability: Unix.
New in version 2.4.
Set the current process’s user id. Availability: Unix.
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.
Unset (delete) the environment variable named varname. Such changes to the environment affect subprocesses started with os.system(), popen() or fork() and execv(). Availability: most flavors of Unix, Windows.
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.
These functions create new file objects. (See also open().)
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: 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).
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.
There are a number of different popen*() functions that provide slightly different ways to create subprocesses.
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.
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.
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.
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.
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.
Close file descriptor fd. Availability: Unix, Windows.
Close all file descriptors from fd_low (inclusive) to fd_high (exclusive), ignoring errors. Availability: Unix, Windows. Equivalent to:
for fd in xrange(fd_low, fd_high):
try:
os.close(fd)
except OSError:
pass
New in version 2.6.
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.
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.
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. Availability: Unix.
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.
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.
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. Availability: Unix, Windows.
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 below).
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.
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.
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.
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 <http://msdn.microsoft.com/en-us/library/z0kc8e3z.aspx> on Windows.
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.
Change the current working directory to path. Availability: Unix, Windows.
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.
Return a Unicode object representing the current working directory. Availability: Unix, Windows.
New in version 2.3.
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):
Availability: Unix.
New in version 2.6.
Change the root directory of the current process to path. Availability: Unix.
New in version 2.2.
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.
Set the flags of path to the numeric flags, like chflags(), but do not follow symbolic links. Availability: Unix.
New in version 2.6.
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.
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.
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.
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.
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.
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.
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.
Compose a raw device number from the major and minor device numbers.
New in version 2.3.
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. Availability: Unix, Windows.
It is also possible to create temporary directories; see the tempfile module’s tempfile.mkdtemp() function.
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.
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.
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. Availability: Unix.
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.
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.
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.
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.
Perform a stat() system call on the given path. 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):
>>> 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: 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 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.)
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: Added access to values as attributes of the returned object.
Changed in version 2.5: Added st_gen and st_birthtime.
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.
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. Availability: Unix.
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.
Changed in version 2.2: Added access to values as attributes of the returned object.
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.
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).
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.
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: 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.
These functions may be used to create and manage processes.
The various exec*() functions take a list of arguments for the new program loaded into the process. In each case, the first of these arguments is passed to the new program as its own name rather than as an argument a user may have typed on a command line. For the C programmer, this is the argv[0] passed to a program’s main(). For example, os.execv('/bin/echo', ['foo', 'bar']) will only print bar on standard output; foo will seem to be ignored.
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.
Exit to the system with status n, without calling cleanup handlers, flushing stdio buffers, etc. Availability: Unix, Windows.
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.
Exit code that means no error occurred. Availability: Unix.
New in version 2.3.
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.
Exit code that means the input data was incorrect. Availability: Unix.
New in version 2.3.
Exit code that means an input file did not exist or was not readable. Availability: Unix.
New in version 2.3.
Exit code that means a specified user did not exist. Availability: Unix.
New in version 2.3.
Exit code that means a specified host did not exist. Availability: Unix.
New in version 2.3.
Exit code that means that a required service is unavailable. Availability: Unix.
New in version 2.3.
Exit code that means an internal software error was detected. Availability: Unix.
New in version 2.3.
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.
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.
Exit code that means a user specified output file could not be created. Availability: Unix.
New in version 2.3.
Exit code that means that an error occurred while doing I/O on some file. Availability: Unix.
New in version 2.3.
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.
Exit code that means that a protocol exchange was illegal, invalid, or not understood. Availability: Unix.
New in version 2.3.
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.
Exit code that means that some kind of configuration error occurred. Availability: Unix.
New in version 2.3.
Exit code that means something like “an entry was not found”. Availability: Unix.
New in version 2.3.
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.
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.
Send the signal sig to the process group pgid. Availability: Unix.
New in version 2.3.
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.
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.
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.
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.
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 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 2.5: The operation parameter.
Execute the command (a string) in a subshell. This is implemented by calling the Standard C function system(), and has the same limitations. Changes to os.environ, 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 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.
Availability: Unix, Windows.
The subprocess module provides more powerful facilities for spawning new processes and retrieving their results; using that module is preferable to using this function. Use the subprocess module. Check especially the Replacing Older Functions with the subprocess Module section.
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.
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.
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.
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.
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.
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.
Return True if a core dump was generated for the process, otherwise return False. Availability: Unix.
New in version 2.3.
Return True if the process has been continued from a job control stop, otherwise return False. Availability: Unix.
New in version 2.3.
Return string-valued system configuration values. name specifies the configuration value to retrieve; it may be a string which is the name of a defined system value; these names are specified in a number of standards (POSIX, Unix 95, Unix 98, and others). Some platforms define additional names as well. The names known to the host operating system are given as the keys of the confstr_names dictionary. For configuration variables not included in that mapping, passing an integer for name is also accepted. Availability: Unix.
If the configuration value specified by name isn’t defined, None is returned.
If name is a string and is not known, ValueError is raised. If a specific value for name is not supported by the host system, even if it is included in confstr_names, an OSError is raised with errno.EINVAL for the error number.
Return the number of processes in the system run queue averaged over the last 1, 5, and 15 minutes or raises OSError if the load average was unobtainable. Availability: Unix.
New in version 2.3.
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.
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.
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.