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
  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.stat(path)
 249         s2 = os.stat(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     if userhome.endswith('/'):
 332         i += 1
 333     return userhome + path[i:]
 334
 335
 336 # Expand paths containing shell variable substitutions.
 337 # This expands the forms $variable and ${variable} only.
 338 # Non-existent variables are left unchanged.
 339
 340 _varprog = None
 341
 342 def expandvars(path):
 343     """Expand shell variables of form $var and ${var}.  Unknown variables
 344     are left unchanged."""
 345     global _varprog
 346     if '$' not in path:
 347         return path
 348     if not _varprog:
 349         import re
 350         _varprog = re.compile(r'\$(\w+|\{[^}]*\})')
 351     i = 0
 352     while True:
 353         m = _varprog.search(path, i)
 354         if not m:
 355             break
 356         i, j = m.span(0)
 357         name = m.group(1)
 358         if name.startswith('{') and name.endswith('}'):
 359             name = name[1:-1]
 360         if name in os.environ:
 361             tail = path[j:]
 362             path = path[:i] + os.environ[name]
 363             i = len(path)
 364             path += tail
 365         else:
 366             i = j
 367     return path
 368
 369
 370 # Normalize a path, e.g. A//B, A/./B and A/foo/../B all become A/B.
 371 # It should be understood that this may change the meaning of the path
 372 # if it contains symbolic links!
 373
 374 def normpath(path):
 375     """Normalize path, eliminating double slashes, etc."""
 376     if path == '':
 377         return '.'
 378     initial_slashes = path.startswith('/')
 379     # POSIX allows one or two initial slashes, but treats three or more
 380     # as single slash.
 381     if (initial_slashes and
 382         path.startswith('//') and not path.startswith('///')):
 383         initial_slashes = 2
 384     comps = path.split('/')
 385     new_comps = []
 386     for comp in comps:
 387         if comp in ('', '.'):
 388             continue
 389         if (comp != '..' or (not initial_slashes and not new_comps) or
 390              (new_comps and new_comps[-1] == '..')):
 391             new_comps.append(comp)
 392         elif new_comps:
 393             new_comps.pop()
 394     comps = new_comps
 395     path = '/'.join(comps)
 396     if initial_slashes:
 397         path = '/'*initial_slashes + path
 398     return path or '.'
 399
 400
 401 def abspath(path):
 402     """Return an absolute path."""
 403     if not isabs(path):
 404         path = join(os.getcwd(), path)
 405     return normpath(path)
 406
 407
 408 # Return a canonical path (i.e. the absolute location of a file on the
 409 # filesystem).
 410
 411 def realpath(filename):
 412     """Return the canonical path of the specified filename, eliminating any
 413 symbolic links encountered in the path."""
 414     if isabs(filename):
 415         bits = ['/'] + filename.split('/')[1:]
 416     else:
 417         bits = [''] + filename.split('/')
 418
 419     for i in range(2, len(bits)+1):
 420         component = join(*bits[0:i])
 421         # Resolve symbolic links.
 422         if islink(component):
 423             resolved = _resolve_link(component)
 424             if resolved is None:
 425                 # Infinite loop -- return original component + rest of the path
 426                 return abspath(join(*([component] + bits[i:])))
 427             else:
 428                 newpath = join(*([resolved] + bits[i:]))
 429                 return realpath(newpath)
 430
 431     return abspath(filename)
 432
 433
 434 def _resolve_link(path):
 435     """Internal helper function.  Takes a path and follows symlinks
 436     until we either arrive at something that isn't a symlink, or
 437     encounter a path we've seen before (meaning that there's a loop).
 438     """
 439     paths_seen = []
 440     while islink(path):
 441         if path in paths_seen:
 442             # Already seen this path, so we must have a symlink loop
 443             return None
 444         paths_seen.append(path)
 445         # Resolve where the link points to
 446         resolved = os.readlink(path)
 447         if not isabs(resolved):
 448             dir = dirname(path)
 449             path = normpath(join(dir, resolved))
 450         else:
 451             path = normpath(resolved)
 452     return path
 453
 454 supports_unicode_filenames = False