Lib/posixpath.py

   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 import genericpath
  16 import warnings
  17 from genericpath import *
  18
  19 __all__ = ["normcase","isabs","join","splitdrive","split","splitext",
  20            "basename","dirname","commonprefix","getsize","getmtime",
  21            "getatime","getctime","islink","exists","lexists","isdir","isfile",
  22            "ismount","walk","expanduser","expandvars","normpath","abspath",
  23            "samefile","sameopenfile","samestat",
  24            "curdir","pardir","sep","pathsep","defpath","altsep","extsep",
  25            "devnull","realpath","supports_unicode_filenames","relpath"]
  26
  27 # strings representing various path-related bits and pieces
  28 curdir = '.'
  29 pardir = '..'
  30 extsep = '.'
  31 sep = '/'
  32 pathsep = ':'
  33 defpath = ':/bin:/usr/bin'
  34 altsep = None
  35 devnull = '/dev/null'
  36
  37 # Normalize the case of a pathname.  Trivial in Posix, string.lower on Mac.
  38 # On MS-DOS this may also turn slashes into backslashes; however, other
  39 # normalizations (such as optimizing '../' away) are not allowed
  40 # (another function should be defined to do that).
  41
  42 def normcase(s):
  43     """Normalize case of pathname.  Has no effect under Posix"""
  44     return s
  45
  46
  47 # Return whether a path is absolute.
  48 # Trivial in Posix, harder on the Mac or MS-DOS.
  49
  50 def isabs(s):
  51     """Test whether a path is absolute"""
  52     return s.startswith('/')
  53
  54
  55 # Join pathnames.
  56 # Ignore the previous parts if a part is absolute.
  57 # Insert a '/' unless the first part is empty or already ends in '/'.
  58
  59 def join(a, *p):
  60     """Join two or more pathname components, inserting '/' as needed.
  61     If any component is an absolute path, all previous path components
  62     will be discarded."""
  63     path = a
  64     for b in p:
  65         if b.startswith('/'):
  66             path = b
  67         elif path == '' or path.endswith('/'):
  68             path +=  b
  69         else:
  70             path += '/' + b
  71     return path
  72
  73
  74 # Split a path in head (everything up to the last '/') and tail (the
  75 # rest).  If the path ends in '/', tail will be empty.  If there is no
  76 # '/' in the path, head  will be empty.
  77 # Trailing '/'es are stripped from head unless it is the root.
  78
  79 def split(p):
  80     """Split a pathname.  Returns tuple "(head, tail)" where "tail" is
  81     everything after the final slash.  Either part may be empty."""
  82     i = p.rfind('/') + 1
  83     head, tail = p[:i], p[i:]
  84     if head and head != '/'*len(head):
  85         head = head.rstrip('/')
  86     return head, tail
  87
  88
  89 # Split a path in root and extension.
  90 # The extension is everything starting at the last dot in the last
  91 # pathname component; the root is everything before that.
  92 # It is always true that root + ext == p.
  93
  94 def splitext(p):
  95     return genericpath._splitext(p, sep, altsep, extsep)
  96 splitext.__doc__ = genericpath._splitext.__doc__
  97
  98 # Split a pathname into a drive specification and the rest of the
  99 # path.  Useful on DOS/Windows/NT; on Unix, the drive is always empty.
 100
 101 def splitdrive(p):
 102     """Split a pathname into drive and path. On Posix, drive is always
 103     empty."""
 104     return '', p
 105
 106
 107 # Return the tail (basename) part of a path, same as split(path)[1].
 108
 109 def basename(p):
 110     """Returns the final component of a pathname"""
 111     i = p.rfind('/') + 1
 112     return p[i:]
 113
 114
 115 # Return the head (dirname) part of a path, same as split(path)[0].
 116
 117 def dirname(p):
 118     """Returns the directory component of a pathname"""
 119     i = p.rfind('/') + 1
 120     head = p[:i]
 121     if head and head != '/'*len(head):
 122         head = head.rstrip('/')
 123     return head
 124
 125
 126 # Is a path a symbolic link?
 127 # This will always return false on systems where os.lstat doesn't exist.
 128
 129 def islink(path):
 130     """Test whether a path is a symbolic link"""
 131     try:
 132         st = os.lstat(path)
 133     except (os.error, AttributeError):
 134         return False
 135     return stat.S_ISLNK(st.st_mode)
 136
 137 # Being true for dangling symbolic links is also useful.
 138
 139 def lexists(path):
 140     """Test whether a path exists.  Returns True for broken symbolic links"""
 141     try:
 142         os.lstat(path)
 143     except os.error:
 144         return False
 145     return True
 146
 147
 148 # Are two filenames really pointing to the same file?
 149
 150 def samefile(f1, f2):
 151     """Test whether two pathnames reference the same actual file"""
 152     s1 = os.stat(f1)
 153     s2 = os.stat(f2)
 154     return samestat(s1, s2)
 155
 156
 157 # Are two open files really referencing the same file?
 158 # (Not necessarily the same file descriptor!)
 159
 160 def sameopenfile(fp1, fp2):
 161     """Test whether two open file objects reference the same file"""
 162     s1 = os.fstat(fp1)
 163     s2 = os.fstat(fp2)
 164     return samestat(s1, s2)
 165
 166
 167 # Are two stat buffers (obtained from stat, fstat or lstat)
 168 # describing the same file?
 169
 170 def samestat(s1, s2):
 171     """Test whether two stat buffers reference the same file"""
 172     return s1.st_ino == s2.st_ino and \
 173            s1.st_dev == s2.st_dev
 174
 175
 176 # Is a path a mount point?
 177 # (Does this work for all UNIXes?  Is it even guaranteed to work by Posix?)
 178
 179 def ismount(path):
 180     """Test whether a path is a mount point"""
 181     try:
 182         s1 = os.lstat(path)
 183         s2 = os.lstat(join(path, '..'))
 184     except os.error:
 185         return False # It doesn't exist -- so not a mount point :-)
 186     dev1 = s1.st_dev
 187     dev2 = s2.st_dev
 188     if dev1 != dev2:
 189         return True     # path/.. on a different device as path
 190     ino1 = s1.st_ino
 191     ino2 = s2.st_ino
 192     if ino1 == ino2:
 193         return True     # path/.. is the same i-node as path
 194     return False
 195
 196
 197 # Directory tree walk.
 198 # For each directory under top (including top itself, but excluding
 199 # '.' and '..'), func(arg, dirname, filenames) is called, where
 200 # dirname is the name of the directory and filenames is the list
 201 # of files (and subdirectories etc.) in the directory.
 202 # The func may modify the filenames list, to implement a filter,
 203 # or to impose a different order of visiting.
 204
 205 def walk(top, func, arg):
 206     """Directory tree walk with callback function.
 207
 208     For each directory in the directory tree rooted at top (including top
 209     itself, but excluding '.' and '..'), call func(arg, dirname, fnames).
 210     dirname is the name of the directory, and fnames a list of the names of
 211     the files and subdirectories in dirname (excluding '.' and '..').  func
 212     may modify the fnames list in-place (e.g. via del or slice assignment),
 213     and walk will only recurse into the subdirectories whose names remain in
 214     fnames; this can be used to implement a filter, or to impose a specific
 215     order of visiting.  No semantics are defined for, or required of, arg,
 216     beyond that arg is always passed to func.  It can be used, e.g., to pass
 217     a filename pattern, or a mutable object designed to accumulate
 218     statistics.  Passing None for arg is common."""
 219     warnings.warnpy3k("In 3.x, os.path.walk is removed in favor of os.walk.",
 220                       stacklevel=2)
 221     try:
 222         names = os.listdir(top)
 223     except os.error:
 224         return
 225     func(arg, top, names)
 226     for name in names:
 227         name = join(top, name)
 228         try:
 229             st = os.lstat(name)
 230         except os.error:
 231             continue
 232         if stat.S_ISDIR(st.st_mode):
 233             walk(name, func, arg)
 234
 235
 236 # Expand paths beginning with '~' or '~user'.
 237 # '~' means $HOME; '~user' means that user's home directory.
 238 # If the path doesn't begin with '~', or if the user or $HOME is unknown,
 239 # the path is returned unchanged (leaving error reporting to whatever
 240 # function is called with the expanded path as argument).
 241 # See also module 'glob' for expansion of *, ? and [...] in pathnames.
 242 # (A function should also be defined to do full *sh-style environment
 243 # variable expansion.)
 244
 245 def expanduser(path):
 246     """Expand ~ and ~user constructions.  If user or $HOME is unknown,
 247     do nothing."""
 248     if not path.startswith('~'):
 249         return path
 250     i = path.find('/', 1)
 251     if i < 0:
 252         i = len(path)
 253     if i == 1:
 254         if 'HOME' not in os.environ:
 255             import pwd
 256             userhome = pwd.getpwuid(os.getuid()).pw_dir
 257         else:
 258             userhome = os.environ['HOME']
 259     else:
 260         import pwd
 261         try:
 262             pwent = pwd.getpwnam(path[1:i])
 263         except KeyError:
 264             return path
 265         userhome = pwent.pw_dir
 266     userhome = userhome.rstrip('/') or userhome
 267     return userhome + path[i:]
 268
 269
 270 # Expand paths containing shell variable substitutions.
 271 # This expands the forms $variable and ${variable} only.
 272 # Non-existent variables are left unchanged.
 273
 274 _varprog = None
 275
 276 def expandvars(path):
 277     """Expand shell variables of form $var and ${var}.  Unknown variables
 278     are left unchanged."""
 279     global _varprog
 280     if '$' not in path:
 281         return path
 282     if not _varprog:
 283         import re
 284         _varprog = re.compile(r'\$(\w+|\{[^}]*\})')
 285     i = 0
 286     while True:
 287         m = _varprog.search(path, i)
 288         if not m:
 289             break
 290         i, j = m.span(0)
 291         name = m.group(1)
 292         if name.startswith('{') and name.endswith('}'):
 293             name = name[1:-1]
 294         if name in os.environ:
 295             tail = path[j:]
 296             path = path[:i] + os.environ[name]
 297             i = len(path)
 298             path += tail
 299         else:
 300             i = j
 301     return path
 302
 303
 304 # Normalize a path, e.g. A//B, A/./B and A/foo/../B all become A/B.
 305 # It should be understood that this may change the meaning of the path
 306 # if it contains symbolic links!
 307
 308 def normpath(path):
 309     """Normalize path, eliminating double slashes, etc."""
 310     # Preserve unicode (if path is unicode)
 311     slash, dot = (u'/', u'.') if isinstance(path, unicode) else ('/', '.')
 312     if path == '':
 313         return dot
 314     initial_slashes = path.startswith('/')
 315     # POSIX allows one or two initial slashes, but treats three or more
 316     # as single slash.
 317     if (initial_slashes and
 318         path.startswith('//') and not path.startswith('///')):
 319         initial_slashes = 2
 320     comps = path.split('/')
 321     new_comps = []
 322     for comp in comps:
 323         if comp in ('', '.'):
 324             continue
 325         if (comp != '..' or (not initial_slashes and not new_comps) or
 326              (new_comps and new_comps[-1] == '..')):
 327             new_comps.append(comp)
 328         elif new_comps:
 329             new_comps.pop()
 330     comps = new_comps
 331     path = slash.join(comps)
 332     if initial_slashes:
 333         path = slash*initial_slashes + path
 334     return path or dot
 335
 336
 337 def abspath(path):
 338     """Return an absolute path."""
 339     if not isabs(path):
 340         if isinstance(path, unicode):
 341             cwd = os.getcwdu()
 342         else:
 343             cwd = os.getcwd()
 344         path = join(cwd, path)
 345     return normpath(path)
 346
 347
 348 # Return a canonical path (i.e. the absolute location of a file on the
 349 # filesystem).
 350
 351 def realpath(filename):
 352     """Return the canonical path of the specified filename, eliminating any
 353 symbolic links encountered in the path."""
 354     if isabs(filename):
 355         bits = ['/'] + filename.split('/')[1:]
 356     else:
 357         bits = [''] + filename.split('/')
 358
 359     for i in range(2, len(bits)+1):
 360         component = join(*bits[0:i])
 361         # Resolve symbolic links.
 362         if islink(component):
 363             resolved = _resolve_link(component)
 364             if resolved is None:
 365                 # Infinite loop -- return original component + rest of the path
 366                 return abspath(join(*([component] + bits[i:])))
 367             else:
 368                 newpath = join(*([resolved] + bits[i:]))
 369                 return realpath(newpath)
 370
 371     return abspath(filename)
 372
 373
 374 def _resolve_link(path):
 375     """Internal helper function.  Takes a path and follows symlinks
 376     until we either arrive at something that isn't a symlink, or
 377     encounter a path we've seen before (meaning that there's a loop).
 378     """
 379     paths_seen = set()
 380     while islink(path):
 381         if path in paths_seen:
 382             # Already seen this path, so we must have a symlink loop
 383             return None
 384         paths_seen.add(path)
 385         # Resolve where the link points to
 386         resolved = os.readlink(path)
 387         if not isabs(resolved):
 388             dir = dirname(path)
 389             path = normpath(join(dir, resolved))
 390         else:
 391             path = normpath(resolved)
 392     return path
 393
 394 supports_unicode_filenames = False
 395
 396 def relpath(path, start=curdir):
 397     """Return a relative version of a path"""
 398
 399     if not path:
 400         raise ValueError("no path specified")
 401
 402     start_list = abspath(start).split(sep)
 403     path_list = abspath(path).split(sep)
 404
 405     # Work out how much of the filepath is shared by start and path.
 406     i = len(commonprefix([start_list, path_list]))
 407
 408     rel_list = [pardir] * (len(start_list)-i) + path_list[i:]
 409     if not rel_list:
 410         return curdir
 411     return join(*rel_list)