/python/Lib/posixpath.py

"""Common operations on Posix pathnames.



Instead of importing this module directly, import os and refer to

this module as os.path.  The "os.path" name is an alias for this

module on Posix systems; on other systems (e.g. Mac, Windows),

os.path provides the same operations in a manner specific to that

platform, and is an alias to another module (e.g. macpath, ntpath).



Some of this can actually be useful on non-Posix systems too, e.g.

for manipulation of the pathname component of URLs.

"""



import os

import stat

import genericpath

import warnings

from genericpath import *



__all__ = ["normcase","isabs","join","splitdrive","split","splitext",

           "basename","dirname","commonprefix","getsize","getmtime",

           "getatime","getctime","islink","exists","lexists","isdir","isfile",

           "ismount","walk","expanduser","expandvars","normpath","abspath",

           "samefile","sameopenfile","samestat",

           "curdir","pardir","sep","pathsep","defpath","altsep","extsep",

           "devnull","realpath","supports_unicode_filenames","relpath"]



# strings representing various path-related bits and pieces

curdir = '.'

pardir = '..'

extsep = '.'

sep = '/'

pathsep = ':'

defpath = ':/bin:/usr/bin'

altsep = None

devnull = '/dev/null'



# Normalize the case of a pathname.  Trivial in Posix, string.lower on Mac.

# On MS-DOS this may also turn slashes into backslashes; however, other

# normalizations (such as optimizing '../' away) are not allowed

# (another function should be defined to do that).



def normcase(s):

    """Normalize case of pathname.  Has no effect under Posix"""

    return s





# Return whether a path is absolute.

# Trivial in Posix, harder on the Mac or MS-DOS.



def isabs(s):

    """Test whether a path is absolute"""

    return s.startswith('/')





# Join pathnames.

# Ignore the previous parts if a part is absolute.

# Insert a '/' unless the first part is empty or already ends in '/'.



def join(a, *p):

    """Join two or more pathname components, inserting '/' as needed.

    If any component is an absolute path, all previous path components

    will be discarded."""

    path = a

    for b in p:

        if b.startswith('/'):

            path = b

        elif path == '' or path.endswith('/'):

            path +=  b

        else:

            path += '/' + b

    return path





# Split a path in head (everything up to the last '/') and tail (the

# rest).  If the path ends in '/', tail will be empty.  If there is no

# '/' in the path, head  will be empty.

# Trailing '/'es are stripped from head unless it is the root.



def split(p):

    """Split a pathname.  Returns tuple "(head, tail)" where "tail" is

    everything after the final slash.  Either part may be empty."""

    i = p.rfind('/') + 1

    head, tail = p[:i], p[i:]

    if head and head != '/'*len(head):

        head = head.rstrip('/')

    return head, tail





# Split a path in root and extension.

# The extension is everything starting at the last dot in the last

# pathname component; the root is everything before that.

# It is always true that root + ext == p.



def splitext(p):

    return genericpath._splitext(p, sep, altsep, extsep)

splitext.__doc__ = genericpath._splitext.__doc__



# Split a pathname into a drive specification and the rest of the

# path.  Useful on DOS/Windows/NT; on Unix, the drive is always empty.



def splitdrive(p):

    """Split a pathname into drive and path. On Posix, drive is always

    empty."""

    return '', p





# Return the tail (basename) part of a path, same as split(path)[1].



def basename(p):

    """Returns the final component of a pathname"""

    i = p.rfind('/') + 1

    return p[i:]





# Return the head (dirname) part of a path, same as split(path)[0].



def dirname(p):

    """Returns the directory component of a pathname"""

    i = p.rfind('/') + 1

    head = p[:i]

    if head and head != '/'*len(head):

        head = head.rstrip('/')

    return head





# Is a path a symbolic link?

# This will always return false on systems where os.lstat doesn't exist.



def islink(path):

    """Test whether a path is a symbolic link"""

    try:

        st = os.lstat(path)

    except (os.error, AttributeError):

        return False

    return stat.S_ISLNK(st.st_mode)



# Being true for dangling symbolic links is also useful.



def lexists(path):

    """Test whether a path exists.  Returns True for broken symbolic links"""

    try:

        st = os.lstat(path)

    except os.error:

        return False

    return True





# Are two filenames really pointing to the same file?



def samefile(f1, f2):

    """Test whether two pathnames reference the same actual file"""

    s1 = os.stat(f1)

    s2 = os.stat(f2)

    return samestat(s1, s2)





# Are two open files really referencing the same file?

# (Not necessarily the same file descriptor!)



def sameopenfile(fp1, fp2):

    """Test whether two open file objects reference the same file"""

    s1 = os.fstat(fp1)

    s2 = os.fstat(fp2)

    return samestat(s1, s2)





# Are two stat buffers (obtained from stat, fstat or lstat)

# describing the same file?



def samestat(s1, s2):

    """Test whether two stat buffers reference the same file"""

    return s1.st_ino == s2.st_ino and \

           s1.st_dev == s2.st_dev





# Is a path a mount point?

# (Does this work for all UNIXes?  Is it even guaranteed to work by Posix?)



def ismount(path):

    """Test whether a path is a mount point"""

    try:

        s1 = os.lstat(path)

        s2 = os.lstat(join(path, '..'))

    except os.error:

        return False # It doesn't exist -- so not a mount point :-)

    dev1 = s1.st_dev

    dev2 = s2.st_dev

    if dev1 != dev2:

        return True     # path/.. on a different device as path

    ino1 = s1.st_ino

    ino2 = s2.st_ino

    if ino1 == ino2:

        return True     # path/.. is the same i-node as path

    return False





# Directory tree walk.

# For each directory under top (including top itself, but excluding

# '.' and '..'), func(arg, dirname, filenames) is called, where

# dirname is the name of the directory and filenames is the list

# of files (and subdirectories etc.) in the directory.

# The func may modify the filenames list, to implement a filter,

# or to impose a different order of visiting.



def walk(top, func, arg):

    """Directory tree walk with callback function.



    For each directory in the directory tree rooted at top (including top

    itself, but excluding '.' and '..'), call func(arg, dirname, fnames).

    dirname is the name of the directory, and fnames a list of the names of

    the files and subdirectories in dirname (excluding '.' and '..').  func

    may modify the fnames list in-place (e.g. via del or slice assignment),

    and walk will only recurse into the subdirectories whose names remain in

    fnames; this can be used to implement a filter, or to impose a specific

    order of visiting.  No semantics are defined for, or required of, arg,

    beyond that arg is always passed to func.  It can be used, e.g., to pass

    a filename pattern, or a mutable object designed to accumulate

    statistics.  Passing None for arg is common."""

    warnings.warnpy3k("In 3.x, os.path.walk is removed in favor of os.walk.")

    try:

        names = os.listdir(top)

    except os.error:

        return

    func(arg, top, names)

    for name in names:

        name = join(top, name)

        try:

            st = os.lstat(name)

        except os.error:

            continue

        if stat.S_ISDIR(st.st_mode):

            walk(name, func, arg)





# Expand paths beginning with '~' or '~user'.

# '~' means $HOME; '~user' means that user's home directory.

# If the path doesn't begin with '~', or if the user or $HOME is unknown,

# the path is returned unchanged (leaving error reporting to whatever

# function is called with the expanded path as argument).

# See also module 'glob' for expansion of *, ? and [...] in pathnames.

# (A function should also be defined to do full *sh-style environment

# variable expansion.)



def expanduser(path):

    """Expand ~ and ~user constructions.  If user or $HOME is unknown,

    do nothing."""

    if not path.startswith('~'):

        return path

    i = path.find('/', 1)

    if i < 0:

        i = len(path)

    if i == 1:

        if 'HOME' not in os.environ:

            import pwd

            userhome = pwd.getpwuid(os.getuid()).pw_dir

        else:

            userhome = os.environ['HOME']

    else:

        import pwd

        try:

            pwent = pwd.getpwnam(path[1:i])

        except KeyError:

            return path

        userhome = pwent.pw_dir

    userhome = userhome.rstrip('/')

    return userhome + path[i:]





# Expand paths containing shell variable substitutions.

# This expands the forms $variable and ${variable} only.

# Non-existent variables are left unchanged.



_varprog = None



def expandvars(path):

    """Expand shell variables of form $var and ${var}.  Unknown variables

    are left unchanged."""

    global _varprog

    if '$' not in path:

        return path

    if not _varprog:

        import re

        _varprog = re.compile(r'\$(\w+|\{[^}]*\})')

    i = 0

    while True:

        m = _varprog.search(path, i)

        if not m:

            break

        i, j = m.span(0)

        name = m.group(1)

        if name.startswith('{') and name.endswith('}'):

            name = name[1:-1]

        if name in os.environ:

            tail = path[j:]

            path = path[:i] + os.environ[name]

            i = len(path)

            path += tail

        else:

            i = j

    return path





# Normalize a path, e.g. A//B, A/./B and A/foo/../B all become A/B.

# It should be understood that this may change the meaning of the path

# if it contains symbolic links!



def normpath(path):

    """Normalize path, eliminating double slashes, etc."""

    if path == '':

        return '.'

    initial_slashes = path.startswith('/')

    # POSIX allows one or two initial slashes, but treats three or more

    # as single slash.

    if (initial_slashes and

        path.startswith('//') and not path.startswith('///')):

        initial_slashes = 2

    comps = path.split('/')

    new_comps = []

    for comp in comps:

        if comp in ('', '.'):

            continue

        if (comp != '..' or (not initial_slashes and not new_comps) or

             (new_comps and new_comps[-1] == '..')):

            new_comps.append(comp)

        elif new_comps:

            new_comps.pop()

    comps = new_comps

    path = '/'.join(comps)

    if initial_slashes:

        path = '/'*initial_slashes + path

    return path or '.'





def abspath(path):

    """Return an absolute path."""

    if not isabs(path):

        path = join(os.getcwd(), path)

    return normpath(path)





# Return a canonical path (i.e. the absolute location of a file on the

# filesystem).



def realpath(filename):

    """Return the canonical path of the specified filename, eliminating any

symbolic links encountered in the path."""

    if isabs(filename):

        bits = ['/'] + filename.split('/')[1:]

    else:

        bits = [''] + filename.split('/')



    for i in range(2, len(bits)+1):

        component = join(*bits[0:i])

        # Resolve symbolic links.

        if islink(component):

            resolved = _resolve_link(component)

            if resolved is None:

                # Infinite loop -- return original component + rest of the path

                return abspath(join(*([component] + bits[i:])))

            else:

                newpath = join(*([resolved] + bits[i:]))

                return realpath(newpath)



    return abspath(filename)





def _resolve_link(path):

    """Internal helper function.  Takes a path and follows symlinks

    until we either arrive at something that isn't a symlink, or

    encounter a path we've seen before (meaning that there's a loop).

    """

    paths_seen = []

    while islink(path):

        if path in paths_seen:

            # Already seen this path, so we must have a symlink loop

            return None

        paths_seen.append(path)

        # Resolve where the link points to

        resolved = os.readlink(path)

        if not isabs(resolved):

            dir = dirname(path)

            path = normpath(join(dir, resolved))

        else:

            path = normpath(resolved)

    return path



supports_unicode_filenames = False



def relpath(path, start=curdir):

    """Return a relative version of a path"""



    if not path:

        raise ValueError("no path specified")



    start_list = abspath(start).split(sep)

    path_list = abspath(path).split(sep)



    # Work out how much of the filepath is shared by start and path.

    i = len(commonprefix([start_list, path_list]))



    rel_list = [pardir] * (len(start_list)-i) + path_list[i:]

    if not rel_list:

        return curdir

    return join(*rel_list)