1 """Common operations on Posix pathnames.

     2 

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

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

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

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

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

     8 

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

    10 for manipulation of the pathname component of URLs.

    11 """

    12 

    13 import os

    14 import stat

    15 

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

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

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

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

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

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

    22            "devnull","realpath","supports_unicode_filenames"]

    23 

    24 # strings representing various path-related bits and pieces

    25 curdir = '.'

    26 pardir = '..'

    27 extsep = '.'

    28 sep = '/'

    29 pathsep = ':'

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

    31 altsep = None

    32 devnull = '/dev/null'

    33 

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

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

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

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

    38 

    39 def normcase(s):

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

    41     return s

    42 

    43 

    44 # Return whether a path is absolute.

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

    46 

    47 def isabs(s):

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

    49     return s.startswith('/')

    50 

    51 

    52 # Join pathnames.

    53 # Ignore the previous parts if a part is absolute.

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

    55 

    56 def join(a, *p):

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

    58     path = a

    59     for b in p:

    60         if b.startswith('/'):

    61             path = b

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

    63             path +=  b

    64         else:

    65             path += '/' + b

    66     return path

    67 

    68 

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

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

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

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

    73 

    74 def split(p):

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

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

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

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

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

    80         head = head.rstrip('/')

    81     return head, tail

    82 

    83 

    84 # Split a path in root and extension.

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

    86 # pathname component; the root is everything before that.

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

    88 

    89 def splitext(p):

    90     """Split the extension from a pathname.  Extension is everything from the

    91     last dot to the end.  Returns "(root, ext)", either part may be empty."""

    92     i = p.rfind('.')

    93     if i<=p.rfind('/'):

    94         return p, ''

    95     else:

    96         return p[:i], p[i:]

    97 

    98 

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

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

   101 

   102 def splitdrive(p):

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

   104     empty."""

   105     return '', p

   106 

   107 

   108 # Return the tail (basename) part of a path.

   109 

   110 def basename(p):

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

   112     return split(p)[1]

   113 

   114 

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

   116 

   117 def dirname(p):

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

   119     return split(p)[0]

   120 

   121 

   122 # Return the longest prefix of all list elements.

   123 

   124 def commonprefix(m):

   125     "Given a list of pathnames, returns the longest common leading component"

   126     if not m: return ''

   127     s1 = min(m)

   128     s2 = max(m)

   129     n = min(len(s1), len(s2))

   130     for i in xrange(n):

   131         if s1[i] != s2[i]:

   132             return s1[:i]

   133     return s1[:n]

   134 

   135 # Get size, mtime, atime of files.

   136 

   137 def getsize(filename):

   138     """Return the size of a file, reported by os.stat()."""

   139     return os.stat(filename).st_size

   140 

   141 def getmtime(filename):

   142     """Return the last modification time of a file, reported by os.stat()."""

   143     return os.stat(filename).st_mtime

   144 

   145 def getatime(filename):

   146     """Return the last access time of a file, reported by os.stat()."""

   147     return os.stat(filename).st_atime

   148 

   149 def getctime(filename):

   150     """Return the metadata change time of a file, reported by os.stat()."""

   151     return os.stat(filename).st_ctime

   152 

   153 # Is a path a symbolic link?

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

   155 

   156 def islink(path):

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

   158     try:

   159         st = os.lstat(path)

   160     except (os.error, AttributeError):

   161         return False

   162     return stat.S_ISLNK(st.st_mode)

   163 

   164 

   165 # Does a path exist?

   166 # This is false for dangling symbolic links.

   167 

   168 def exists(path):

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

   170     try:

   171         st = os.stat(path)

   172     except os.error:

   173         return False

   174     return True

   175 

   176 

   177 # Being true for dangling symbolic links is also useful.

   178 

   179 def lexists(path):

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

   181     try:

   182         st = os.lstat(path)

   183     except os.error:

   184         return False

   185     return True

   186 

   187 

   188 # Is a path a directory?

   189 # This follows symbolic links, so both islink() and isdir() can be true

   190 # for the same path.

   191 

   192 def isdir(path):

   193     """Test whether a path is a directory"""

   194     try:

   195         st = os.stat(path)

   196     except os.error:

   197         return False

   198     return stat.S_ISDIR(st.st_mode)

   199 

   200 

   201 # Is a path a regular file?

   202 # This follows symbolic links, so both islink() and isfile() can be true

   203 # for the same path.

   204 

   205 def isfile(path):

   206     """Test whether a path is a regular file"""

   207     try:

   208         st = os.stat(path)

   209     except os.error:

   210         return False

   211     return stat.S_ISREG(st.st_mode)

   212 

   213 

   214 # Are two filenames really pointing to the same file?

   215 

   216 def samefile(f1, f2):

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

   218     s1 = os.stat(f1)

   219     s2 = os.stat(f2)

   220     return samestat(s1, s2)

   221 

   222 

   223 # Are two open files really referencing the same file?

   224 # (Not necessarily the same file descriptor!)

   225 

   226 def sameopenfile(fp1, fp2):

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

   228     s1 = os.fstat(fp1)

   229     s2 = os.fstat(fp2)

   230     return samestat(s1, s2)

   231 

   232 

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

   234 # describing the same file?

   235 

   236 def samestat(s1, s2):

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

   238     return s1.st_ino == s2.st_ino and \

   239            s1.st_dev == s2.st_dev

   240 

   241 

   242 # Is a path a mount point?

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

   244 

   245 def ismount(path):

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

   247     try:

   248         s1 = os.lstat(path)

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

   250     except os.error:

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

   252     dev1 = s1.st_dev

   253     dev2 = s2.st_dev

   254     if dev1 != dev2:

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

   256     ino1 = s1.st_ino

   257     ino2 = s2.st_ino

   258     if ino1 == ino2:

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

   260     return False

   261 

   262 

   263 # Directory tree walk.

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

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

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

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

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

   269 # or to impose a different order of visiting.

   270 

   271 def walk(top, func, arg):

   272     """Directory tree walk with callback function.

   273 

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

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

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

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

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

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

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

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

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

   283     a filename pattern, or a mutable object designed to accumulate

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

   285 

   286     try:

   287         names = os.listdir(top)

   288     except os.error:

   289         return

   290     func(arg, top, names)

   291     for name in names:

   292         name = join(top, name)

   293         try:

   294             st = os.lstat(name)

   295         except os.error:

   296             continue

   297         if stat.S_ISDIR(st.st_mode):

   298             walk(name, func, arg)

   299 

   300 

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

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

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

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

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

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

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

   308 # variable expansion.)

   309 

   310 def expanduser(path):

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

   312     do nothing."""

   313     if not path.startswith('~'):

   314         return path

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

   316     if i < 0:

   317         i = len(path)

   318     if i == 1:

   319         if 'HOME' not in os.environ:

   320             import pwd

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

   322         else:

   323             userhome = os.environ['HOME']

   324     else:

   325         import pwd

   326         try:

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

   328         except KeyError:

   329             return path

   330         userhome = pwent.pw_dir

   331     userhome = userhome.rstrip('/')

   332     return userhome + path[i:]

   333 

   334 

   335 # Expand paths containing shell variable substitutions.

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

   337 # Non-existent variables are left unchanged.

   338 

   339 _varprog = None

   340 

   341 def expandvars(path):

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

   343     are left unchanged."""

   344     global _varprog

   345     if '$' not in path:

   346         return path

   347     if not _varprog:

   348         import re

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

   350     i = 0

   351     while True:

   352         m = _varprog.search(path, i)

   353         if not m:

   354             break

   355         i, j = m.span(0)

   356         name = m.group(1)

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

   358             name = name[1:-1]

   359         if name in os.environ:

   360             tail = path[j:]

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

   362             i = len(path)

   363             path += tail

   364         else:

   365             i = j

   366     return path

   367 

   368 

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

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

   371 # if it contains symbolic links!

   372 

   373 def normpath(path):

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

   375     if path == '':

   376         return '.'

   377     initial_slashes = path.startswith('/')

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

   379     # as single slash.

   380     if (initial_slashes and

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

   382         initial_slashes = 2

   383     comps = path.split('/')

   384     new_comps = []

   385     for comp in comps:

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

   387             continue

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

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

   390             new_comps.append(comp)

   391         elif new_comps:

   392             new_comps.pop()

   393     comps = new_comps

   394     path = '/'.join(comps)

   395     if initial_slashes:

   396         path = '/'*initial_slashes + path

   397     return path or '.'

   398 

   399 

   400 def abspath(path):

   401     """Return an absolute path."""

   402     if not isabs(path):

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

   404     return normpath(path)

   405 

   406 

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

   408 # filesystem).

   409 

   410 def realpath(filename):

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

   412 symbolic links encountered in the path."""

   413     if isabs(filename):

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

   415     else:

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

   417 

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

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

   420         # Resolve symbolic links.

   421         if islink(component):

   422             resolved = _resolve_link(component)

   423             if resolved is None:

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

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

   426             else:

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

   428                 return realpath(newpath)

   429 

   430     return abspath(filename)

   431 

   432 

   433 def _resolve_link(path):

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

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

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

   437     """

   438     paths_seen = []

   439     while islink(path):

   440         if path in paths_seen:

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

   442             return None

   443         paths_seen.append(path)

   444         # Resolve where the link points to

   445         resolved = os.readlink(path)

   446         if not isabs(resolved):

   447             dir = dirname(path)

   448             path = normpath(join(dir, resolved))

   449         else:

   450             path = normpath(resolved)

   451     return path

   452 

   453 supports_unicode_filenames = False