Lib/posixpath.py

   1 # Module 'posixpath' -- common operations on POSIX pathnames
   2
   3 import posix
   4 import stat
   5
   6
   7 # Normalize the case of a pathname.  Trivial in Posix, string.lower on Mac.
   8 # On MS-DOS this may also turn slashes into backslashes; however, other
   9 # normalizations (such as optimizing '../' away) are not allowed
  10 # (another function should be defined to do that).
  11
  12 def normcase(s):
  13         return s
  14
  15
  16 # Return wheter a path is absolute.
  17 # Trivial in Posix, harder on the Mac or MS-DOS.
  18
  19 def isabs(s):
  20         return s[:1] == '/'
  21
  22
  23 # Join two pathnames.
  24 # Ignore the first part if the second part is absolute.
  25 # Insert a '/' unless the first part is empty or already ends in '/'.
  26
  27 def join(a, b):
  28         if b[:1] == '/': return b
  29         if a == '' or a[-1:] == '/': return a + b
  30         # Note: join('x', '') returns 'x/'; is this what we want?
  31         return a + '/' + b
  32
  33
  34 # Split a path in head (everything up to the last '/') and tail (the
  35 # rest).  If the original path ends in '/' but is not the root, this
  36 # '/' is stripped.  After the trailing '/' is stripped, the invariant
  37 # join(head, tail) == p holds.
  38 # The resulting head won't end in '/' unless it is the root.
  39
  40 def split(p):
  41         if p[-1:] == '/' and p <> '/'*len(p):
  42                 while p[-1] == '/':
  43                         p = p[:-1]
  44         head, tail = '', ''
  45         for c in p:
  46                 tail = tail + c
  47                 if c == '/':
  48                         head, tail = head + tail, ''
  49         if head[-1:] == '/' and head <> '/'*len(head):
  50                 while head[-1] == '/':
  51                         head = head[:-1]
  52         return head, tail
  53
  54
  55 # Split a path in root and extension.
  56 # The extension is everything starting at the first dot in the last
  57 # pathname component; the root is everything before that.
  58 # It is always true that root + ext == p.
  59
  60 def splitext(p):
  61         root, ext = '', ''
  62         for c in p:
  63                 if c == '/':
  64                         root, ext = root + ext + c, ''
  65                 elif c == '.' or ext:
  66                         ext = ext + c
  67                 else:
  68                         root = root + c
  69         return root, ext
  70
  71
  72 # Return the tail (basename) part of a path.
  73
  74 def basename(p):
  75         return split(p)[1]
  76
  77
  78 # Return the head (dirname) part of a path.
  79
  80 def dirname(p):
  81         return split(p)[0]
  82
  83
  84 # Return the longest prefix of all list elements.
  85
  86 def commonprefix(m):
  87         if not m: return ''
  88         prefix = m[0]
  89         for item in m:
  90                 for i in range(len(prefix)):
  91                         if prefix[:i+1] <> item[:i+1]:
  92                                 prefix = prefix[:i]
  93                                 if i == 0: return ''
  94                                 break
  95         return prefix
  96
  97
  98 # Is a path a symbolic link?
  99 # This will always return false on systems where posix.lstat doesn't exist.
 100
 101 def islink(path):
 102         try:
 103                 st = posix.lstat(path)
 104         except (posix.error, AttributeError):
 105                 return 0
 106         return stat.S_ISLNK(st[stat.ST_MODE])
 107
 108
 109 # Does a path exist?
 110 # This is false for dangling symbolic links.
 111
 112 def exists(path):
 113         try:
 114                 st = posix.stat(path)
 115         except posix.error:
 116                 return 0
 117         return 1
 118
 119
 120 # Is a path a posix directory?
 121 # This follows symbolic links, so both islink() and isdir() can be true
 122 # for the same path.
 123
 124 def isdir(path):
 125         try:
 126                 st = posix.stat(path)
 127         except posix.error:
 128                 return 0
 129         return stat.S_ISDIR(st[stat.ST_MODE])
 130
 131
 132 # Is a path a regular file?
 133 # This follows symbolic links, so both islink() and isdir() can be true
 134 # for the same path.
 135
 136 def isfile(path):
 137         try:
 138                 st = posix.stat(path)
 139         except posix.error:
 140                 return 0
 141         return stat.S_ISREG(st[stat.ST_MODE])
 142
 143
 144 # Are two filenames really pointing to the same file?
 145
 146 def samefile(f1, f2):
 147         s1 = posix.stat(f1)
 148         s2 = posix.stat(f2)
 149         return samestat(s1, s2)
 150
 151
 152 # Are two open files really referencing the same file?
 153 # (Not necessarily the same file descriptor!)
 154 # XXX Oops, posix.fstat() doesn't exist yet!
 155
 156 def sameopenfile(fp1, fp2):
 157         s1 = posix.fstat(fp1)
 158         s2 = posix.fstat(fp2)
 159         return samestat(s1, s2)
 160
 161
 162 # Are two stat buffers (obtained from stat, fstat or lstat)
 163 # describing the same file?
 164
 165 def samestat(s1, s2):
 166         return s1[stat.ST_INO] == s2[stat.ST_INO] and \
 167                 s1[stat.ST_DEV] == s2[stat.ST_DEV]
 168
 169
 170 # Is a path a mount point?
 171 # (Does this work for all UNIXes?  Is it even guaranteed to work by POSIX?)
 172
 173 def ismount(path):
 174         try:
 175                 s1 = posix.stat(path)
 176                 s2 = posix.stat(join(path, '..'))
 177         except posix.error:
 178                 return 0 # It doesn't exist -- so not a mount point :-)
 179         dev1 = s1[stat.ST_DEV]
 180         dev2 = s2[stat.ST_DEV]
 181         if dev1 != dev2:
 182                 return 1                # path/.. on a different device as path
 183         ino1 = s1[stat.ST_INO]
 184         ino2 = s2[stat.ST_INO]
 185         if ino1 == ino2:
 186                 return 1                # path/.. is the same i-node as path
 187         return 0
 188
 189
 190 # Directory tree walk.
 191 # For each directory under top (including top itself, but excluding
 192 # '.' and '..'), func(arg, dirname, filenames) is called, where
 193 # dirname is the name of the directory and filenames is the list
 194 # files files (and subdirectories etc.) in the directory.
 195 # The func may modify the filenames list, to implement a filter,
 196 # or to impose a different order of visiting.
 197
 198 def walk(top, func, arg):
 199         try:
 200                 names = posix.listdir(top)
 201         except posix.error:
 202                 return
 203         func(arg, top, names)
 204         exceptions = ('.', '..')
 205         for name in names:
 206                 if name not in exceptions:
 207                         name = join(top, name)
 208                         if isdir(name):
 209                                 walk(name, func, arg)
 210
 211
 212 # Expand paths beginning with '~' or '~user'.
 213 # '~' means $HOME; '~user' means that user's home directory.
 214 # If the path doesn't begin with '~', or if the user or $HOME is unknown,
 215 # the path is returned unchanged (leaving error reporting to whatever
 216 # function is called with the expanded path as argument).
 217 # See also module 'glob' for expansion of *, ? and [...] in pathnames.
 218 # (A function should also be defined to do full *sh-style environment
 219 # variable expansion.)
 220
 221 def expanduser(path):
 222         if path[:1] <> '~':
 223                 return path
 224         i, n = 1, len(path)
 225         while i < n and path[i] <> '/':
 226                 i = i+1
 227         if i == 1:
 228                 if not posix.environ.has_key('HOME'):
 229                         return path
 230                 userhome = posix.environ['HOME']
 231         else:
 232                 import pwd
 233                 try:
 234                         pwent = pwd.getpwnam(path[1:i])
 235                 except KeyError:
 236                         return path
 237                 userhome = pwent[5]
 238         return userhome + path[i:]
 239
 240
 241 # Expand paths containing shell variable substitutions.
 242 # This is done by piping it through the shell.
 243 # Shell quoting characters (\ " ' `) are protected by a backslash.
 244 # NB: a future version may avoid starting a subprocess and do the
 245 # substitutions internally.  This may slightly change the syntax
 246 # for variables.
 247
 248 def expandvars(path):
 249         if '$' not in path:
 250                 return path
 251         q = ''
 252         for c in path:
 253                 if c in ('\\', '"', '\'', '`'):
 254                         c = '\\' + c
 255                 q = q + c
 256         d = '!'
 257         if q == d:
 258                 d = '+'
 259         p = posix.popen('cat <<' + d + '\n' + q + '\n' + d + '\n', 'r')
 260         res = p.read()
 261         del p
 262         if res[-1:] == '\n':
 263                 res = res[:-1]
 264         return res
 265
 266
 267 # Normalize a path, e.g. A//B, A/./B and A/foo/../B all become A/B.
 268 # It should be understood that this may change the meaning of the path
 269 # if it contains symbolic links!
 270
 271 def normpath(path):
 272         import string
 273         # Treat initial slashes specially
 274         slashes = ''
 275         while path[:1] == '/':
 276                 slashes = slashes + '/'
 277                 path = path[1:]
 278         comps = string.splitfields(path, '/')
 279         i = 0
 280         while i < len(comps):
 281                 if comps[i] == '.':
 282                         del comps[i]
 283                 elif comps[i] == '..' and i > 0 and \
 284                                           comps[i-1] not in ('', '..'):
 285                         del comps[i-1:i+1]
 286                         i = i-1
 287                 elif comps[i] == '' and i > 0 and comps[i-1] <> '':
 288                         del comps[i]
 289                 else:
 290                         i = i+1
 291         # If the path is now empty, substitute '.'
 292         if not comps and not slashes:
 293                 comps.append('.')
 294         return slashes + string.joinfields(comps, '/')