Lib/posixpath.py

# Module 'posixpath' -- common operations on Posix pathnames.
# Some of this can actually be useful on non-Posix systems too, e.g.
# for manipulation of the pathname component of URLs.
# 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).
"""Common pathname manipulations, Posix version. 
Instead of importing this module
directly, import os and refer to this module as os.path.
"""

import os
import stat


# 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 wheter 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[:1] == '/'


# 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"""
    path = a
    for b in p:
        if b[:1] == '/':
            path = b
        elif path == '' or path[-1:] == '/':
            path = path + b
        else:
            path = 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"""
    import string
    i = string.rfind(p, '/') + 1
    head, tail = p[:i], p[i:]
    if head and head <> '/'*len(head):
        while head[-1] == '/':
            head = head[:-1]
    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):
    """Split the extension from a pathname.  Extension is everything from the
last dot to the end.  Returns "(root, ext)", either part may be empty"""
    root, ext = '', ''
    for c in p:
        if c == '/':
            root, ext = root + ext + c, ''
        elif c == '.':
            if ext:
                root, ext = root + ext, c
            else:
                ext = c
        elif ext:
            ext = ext + c
        else:
            root = root + c
    return root, ext


# 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.

def basename(p):
    """Returns the final component of a pathname"""
    return split(p)[1]


# Return the head (dirname) part of a path.

def dirname(p):
    """Returns the directory component of a pathname"""
    return split(p)[0]


# Return the longest prefix of all list elements.

def commonprefix(m):
    "Given a list of pathnames, returns the longest common leading component"
    if not m: return ''
    prefix = m[0]
    for item in m:
        for i in range(len(prefix)):
            if prefix[:i+1] <> item[:i+1]:
                prefix = prefix[:i]
                if i == 0: return ''
                break
    return prefix


# 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 0
    return stat.S_ISLNK(st[stat.ST_MODE])


# Does a path exist?
# This is false for dangling symbolic links.

def exists(path):
    """Test whether a path exists.  Returns false for broken symbolic links"""
    try:
        st = os.stat(path)
    except os.error:
        return 0
    return 1


# Is a path a directory?
# This follows symbolic links, so both islink() and isdir() can be true
# for the same path.

def isdir(path):
    """Test whether a path is a directory"""
    try:
        st = os.stat(path)
    except os.error:
        return 0
    return stat.S_ISDIR(st[stat.ST_MODE])


# Is a path a regular file?
# This follows symbolic links, so both islink() and isfile() can be true
# for the same path.

def isfile(path):
    """Test whether a path is a regular file"""
    try:
        st = os.stat(path)
    except os.error:
        return 0
    return stat.S_ISREG(st[stat.ST_MODE])


# 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[stat.ST_INO] == s2[stat.ST_INO] and \
	   s1[stat.ST_DEV] == s2[stat.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.stat(path)
        s2 = os.stat(join(path, '..'))
    except os.error:
        return 0 # It doesn't exist -- so not a mount point :-)
    dev1 = s1[stat.ST_DEV]
    dev2 = s2[stat.ST_DEV]
    if dev1 != dev2:
        return 1        # path/.. on a different device as path
    ino1 = s1[stat.ST_INO]
    ino2 = s2[stat.ST_INO]
    if ino1 == ino2:
        return 1        # path/.. is the same i-node as path
    return 0


# 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):
    """walk(top,func,args) calls func(arg, d, files) for each directory "d" 
in the tree  rooted at "top" (including "top" itself).  "files" is a list
of all the files and subdirs in directory "d".
"""
    try:
        names = os.listdir(top)
    except os.error:
        return
    func(arg, top, names)
    exceptions = ('.', '..')
    for name in names:
        if name not in exceptions:
            name = join(top, name)
            if isdir(name) and not islink(name):
                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 path[:1] <> '~':
        return path
    i, n = 1, len(path)
    while i < n and path[i] <> '/':
        i = i+1
    if i == 1:
        if not os.environ.has_key('HOME'):
            return path
        userhome = os.environ['HOME']
    else:
        import pwd
        try:
            pwent = pwd.getpwnam(path[1:i])
        except KeyError:
            return path
        userhome = pwent[5]
    if userhome[-1:] == '/': i = i+1
    return userhome + path[i:]


# Expand paths containing shell variable substitutions.
# This expands the forms $variable and ${variable} only.
# Non-existant 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 1:
        m = _varprog.search(path, i)
        if not m:
            break
        i, j = m.span(0)
        name = m.group(1)
        if name[:1] == '{' and name[-1:] == '}':
            name = name[1:-1]
        if os.environ.has_key(name):
            tail = path[j:]
            path = path[:i] + os.environ[name]
            i = len(path)
            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."""
    import string
    # Treat initial slashes specially
    slashes = ''
    while path[:1] == '/':
        slashes = slashes + '/'
        path = path[1:]
    comps = string.splitfields(path, '/')
    i = 0
    while i < len(comps):
        if comps[i] == '.':
            del comps[i]
        elif comps[i] == '..' and i > 0 and comps[i-1] not in ('', '..'):
            del comps[i-1:i+1]
            i = i-1
        elif comps[i] == '' and i > 0 and comps[i-1] <> '':
            del comps[i]
        else:
            i = i+1
    # If the path is now empty, substitute '.'
    if not comps and not slashes:
        comps.append('.')
    return slashes + string.joinfields(comps, '/')