14.1.4 Files and Directories

Python 2.5

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14.1.4 Files and Directories

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: Macintosh, 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.

F_OK: Value to pass as the mode parameter of access() to test the existence of path.

R_OK: Value to include in the mode parameter of access() to test the readability of path.

W_OK: Value to include in the mode parameter of access() to test the writability of path.

X_OK: Value to include in the mode parameter of access() to determine if path can be executed.

chdir( path): Change the current working directory to path. Availability: Macintosh, Unix, Windows.

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.

getcwd( ): Return a string representing the current working directory. Availability: Macintosh, Unix, Windows.

getcwdu( ): Return a Unicode object representing the current working directory. Availability: Macintosh, Unix, Windows. New in version 2.3.

chroot( path): Change the root directory of the current process to path. Availability: Macintosh, Unix. New in version 2.2.

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 or-ed combinations of them:

S_ISUID
S_ISGID
S_ENFMT
S_ISVTX
S_IREAD
S_IWRITE
S_IEXEC
S_IRWXU
S_IRUSR
S_IWUSR
S_IXUSR
S_IRWXG
S_IRGRP
S_IWGRP
S_IXGRP
S_IRWXO
S_IROTH
S_IWOTH
S_IXOTH

Availability: Macintosh, Unix, Windows.

Note: Although Windows supports chmod(), you can only set the file's read-only flag with it (via the S_IWRITE and S_IREAD constants or a corresponding integer value). All other bits are ignored.

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: Macintosh, Unix.

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: Macintosh, Unix. New in version 2.3.

link( src, dst): Create a hard link pointing to src named dst. Availability: Macintosh, Unix.

listdir( path): Return a list containing the names of the entries in the directory. The list is in arbitrary order. It does not include the special entries '.' and '..' even if they are present in the directory. Availability: Macintosh, 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.

lstat( path): Like stat(), but do not follow symbolic links. Availability: Macintosh, Unix.

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: Macintosh, 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.

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 S_IFREG, S_IFCHR, S_IFBLK, and S_IFIFO (those constants are available in stat). For S_IFCHR and S_IFBLK, device defines the newly created device special file (probably using os.makedev()), otherwise it is ignored. New in version 2.3.

major( device): Extracts the device major number from a raw device number (usually the st_dev or st_rdev field from stat). New in version 2.3.

minor( device): Extracts the device minor number from a raw device number (usually the st_dev or st_rdev field from stat). New in version 2.3.

makedev( major, minor): Composes a raw device number from the major and minor device numbers. New in version 2.3.

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. Availability: Macintosh, Unix, Windows.

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. 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.

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. Availability: Macintosh, 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.

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: Macintosh, Unix.

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). Availability: Macintosh, Unix.

remove( path): Remove 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: Macintosh, Unix, Windows.

removedirs( path): Removes 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.

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 removed 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: Macintosh, Unix, Windows.

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.

rmdir( path): Remove the directory path. Availability: Macintosh, Unix, Windows.

stat( path)

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: Macintosh, 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, st_birthtime.

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.

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. 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.

symlink( src, dst): Create a symbolic link pointing to src named dst. Availability: Unix.

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 the 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 14.1.2) instead. Availability: Macintosh, Unix, Windows.

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 14.1.2) 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).

TMP_MAX: The maximum number of unique names that tmpnam() will generate before reusing names.

unlink( path): Remove the file path. This is the same function as remove(); the unlink() name is its traditional Unix name. Availability: Macintosh, Unix, Windows.

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. 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: Macintosh, Unix, Windows.

walk( top[, topdown=True[, onerror=None]])

walk() generates 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 os.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.

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.

Note: On systems that support symbolic links, links to subdirectories appear in dirnames lists, but walk() will not visit them (infinite loops are hard to avoid when following symbolic links). To visit linked directories, you can identify them with os.path.islink(path), and invoke walk(path) on each directly.

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.

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