mirror of
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83eeef4b06
Once upon a time, I put together a little function
that tries to find the canonical filename for a given
pathname on POSIX. I've finally gotten around to
turning it into a proper patch with documentation.
On non-POSIX, I made it an alias for 'abspath', as
that's the behavior on POSIX when no symlinks are
encountered in the path.
Example:
>>> os.path.realpath('/usr/bin/X11/X')
'/usr/X11R6/bin/X'
336 lines
9.4 KiB
Python
336 lines
9.4 KiB
Python
"""Common operations on DOS pathnames."""
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import os
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import stat
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__all__ = ["normcase","isabs","join","splitdrive","split","splitext",
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"basename","dirname","commonprefix","getsize","getmtime",
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"getatime","islink","exists","isdir","isfile","ismount",
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"walk","expanduser","expandvars","normpath","abspath"]
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def normcase(s):
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"""Normalize the case of a pathname.
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On MS-DOS it maps the pathname to lowercase, turns slashes into
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backslashes.
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Other normalizations (such as optimizing '../' away) are not allowed
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(this is done by normpath).
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Previously, this version mapped invalid consecutive characters to a
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single '_', but this has been removed. This functionality should
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possibly be added as a new function."""
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return s.replace("/", "\\").lower()
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def isabs(s):
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"""Return whether a path is absolute.
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Trivial in Posix, harder on the Mac or MS-DOS.
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For DOS it is absolute if it starts with a slash or backslash (current
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volume), or if a pathname after the volume letter and colon starts with
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a slash or backslash."""
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s = splitdrive(s)[1]
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return s != '' and s[:1] in '/\\'
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def join(a, *p):
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"""Join two (or more) paths."""
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path = a
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for b in p:
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if isabs(b):
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path = b
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elif path == '' or path[-1:] in '/\\:':
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path = path + b
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else:
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path = path + "\\" + b
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return path
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def splitdrive(p):
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"""Split a path into a drive specification (a drive letter followed
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by a colon) and path specification.
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It is always true that drivespec + pathspec == p."""
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if p[1:2] == ':':
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return p[0:2], p[2:]
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return '', p
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def split(p):
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"""Split a path into head (everything up to the last '/') and tail
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(the rest). After the trailing '/' is stripped, the invariant
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join(head, tail) == p holds.
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The resulting head won't end in '/' unless it is the root."""
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d, p = splitdrive(p)
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# set i to index beyond p's last slash
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i = len(p)
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while i and p[i-1] not in '/\\':
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i = i - 1
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head, tail = p[:i], p[i:] # now tail has no slashes
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# remove trailing slashes from head, unless it's all slashes
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head2 = head
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while head2 and head2[-1] in '/\\':
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head2 = head2[:-1]
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head = head2 or head
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return d + head, tail
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def splitext(p):
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"""Split a path into root and extension.
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The extension is everything starting at the first dot in the last
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pathname component; the root is everything before that.
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It is always true that root + ext == p."""
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root, ext = '', ''
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for c in p:
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if c in '/\\':
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root, ext = root + ext + c, ''
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elif c == '.' or ext:
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ext = ext + c
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else:
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root = root + c
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return root, ext
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def basename(p):
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"""Return the tail (basename) part of a path."""
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return split(p)[1]
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def dirname(p):
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"""Return the head (dirname) part of a path."""
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return split(p)[0]
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def commonprefix(m):
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"""Return the longest prefix of all list elements."""
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if not m: return ''
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prefix = m[0]
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for item in m:
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for i in range(len(prefix)):
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if prefix[:i+1] != item[:i+1]:
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prefix = prefix[:i]
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if i == 0: return ''
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break
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return prefix
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# Get size, mtime, atime of files.
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def getsize(filename):
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"""Return the size of a file, reported by os.stat()."""
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st = os.stat(filename)
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return st[stat.ST_SIZE]
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def getmtime(filename):
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"""Return the last modification time of a file, reported by os.stat()."""
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st = os.stat(filename)
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return st[stat.ST_MTIME]
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def getatime(filename):
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"""Return the last access time of a file, reported by os.stat()."""
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st = os.stat(filename)
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return st[stat.ST_ATIME]
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def islink(path):
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"""Is a path a symbolic link?
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This will always return false on systems where posix.lstat doesn't exist."""
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return 0
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def exists(path):
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"""Does a path exist?
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This is false for dangling symbolic links."""
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try:
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st = os.stat(path)
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except os.error:
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return 0
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return 1
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def isdir(path):
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"""Is a path a dos directory?"""
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try:
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st = os.stat(path)
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except os.error:
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return 0
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return stat.S_ISDIR(st[stat.ST_MODE])
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def isfile(path):
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"""Is a path a regular file?"""
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try:
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st = os.stat(path)
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except os.error:
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return 0
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return stat.S_ISREG(st[stat.ST_MODE])
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def ismount(path):
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"""Is a path a mount point?"""
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# XXX This degenerates in: 'is this the root?' on DOS
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return isabs(splitdrive(path)[1])
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def walk(top, func, arg):
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"""Directory tree walk.
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For each directory under top (including top itself, but excluding
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'.' and '..'), func(arg, dirname, filenames) is called, where
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dirname is the name of the directory and filenames is the list
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files files (and subdirectories etc.) in the directory.
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The func may modify the filenames list, to implement a filter,
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or to impose a different order of visiting."""
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try:
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names = os.listdir(top)
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except os.error:
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return
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func(arg, top, names)
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exceptions = ('.', '..')
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for name in names:
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if name not in exceptions:
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name = join(top, name)
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if isdir(name):
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walk(name, func, arg)
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def expanduser(path):
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"""Expand paths beginning with '~' or '~user'.
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'~' means $HOME; '~user' means that user's home directory.
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If the path doesn't begin with '~', or if the user or $HOME is unknown,
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the path is returned unchanged (leaving error reporting to whatever
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function is called with the expanded path as argument).
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See also module 'glob' for expansion of *, ? and [...] in pathnames.
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(A function should also be defined to do full *sh-style environment
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variable expansion.)"""
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if path[:1] != '~':
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return path
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i, n = 1, len(path)
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while i < n and path[i] not in '/\\':
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i = i+1
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if i == 1:
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if not os.environ.has_key('HOME'):
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return path
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userhome = os.environ['HOME']
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else:
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return path
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return userhome + path[i:]
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def expandvars(path):
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"""Expand paths containing shell variable substitutions.
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The following rules apply:
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- no expansion within single quotes
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- no escape character, except for '$$' which is translated into '$'
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- ${varname} is accepted.
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- varnames can be made out of letters, digits and the character '_'"""
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# XXX With COMMAND.COM you can use any characters in a variable name,
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# XXX except '^|<>='.
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if '$' not in path:
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return path
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import string
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varchars = string.ascii_letters + string.digits + "_-"
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res = ''
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index = 0
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pathlen = len(path)
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while index < pathlen:
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c = path[index]
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if c == '\'': # no expansion within single quotes
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path = path[index + 1:]
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pathlen = len(path)
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try:
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index = path.index('\'')
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res = res + '\'' + path[:index + 1]
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except ValueError:
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res = res + path
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index = pathlen -1
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elif c == '$': # variable or '$$'
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if path[index + 1:index + 2] == '$':
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res = res + c
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index = index + 1
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elif path[index + 1:index + 2] == '{':
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path = path[index+2:]
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pathlen = len(path)
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try:
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index = path.index('}')
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var = path[:index]
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if os.environ.has_key(var):
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res = res + os.environ[var]
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except ValueError:
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res = res + path
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index = pathlen - 1
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else:
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var = ''
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index = index + 1
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c = path[index:index + 1]
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while c != '' and c in varchars:
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var = var + c
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index = index + 1
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c = path[index:index + 1]
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if os.environ.has_key(var):
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res = res + os.environ[var]
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if c != '':
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res = res + c
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else:
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res = res + c
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index = index + 1
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return res
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def normpath(path):
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"""Normalize a path, e.g. A//B, A/./B and A/foo/../B all become A/B.
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Also, components of the path are silently truncated to 8+3 notation."""
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path = path.replace("/", "\\")
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prefix, path = splitdrive(path)
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while path[:1] == "\\":
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prefix = prefix + "\\"
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path = path[1:]
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comps = path.split("\\")
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i = 0
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while i < len(comps):
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if comps[i] == '.':
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del comps[i]
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elif comps[i] == '..' and i > 0 and \
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comps[i-1] not in ('', '..'):
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del comps[i-1:i+1]
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i = i - 1
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elif comps[i] == '' and i > 0 and comps[i-1] != '':
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del comps[i]
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elif '.' in comps[i]:
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comp = comps[i].split('.')
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comps[i] = comp[0][:8] + '.' + comp[1][:3]
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i = i + 1
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elif len(comps[i]) > 8:
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comps[i] = comps[i][:8]
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i = i + 1
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else:
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i = i + 1
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# If the path is now empty, substitute '.'
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if not prefix and not comps:
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comps.append('.')
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return prefix + "\\".join(comps)
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def abspath(path):
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"""Return an absolute path."""
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if not isabs(path):
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path = join(os.getcwd(), path)
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return normpath(path)
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# realpath is a no-op on systems without islink support
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realpath = abspath
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