def expandvars(path):    """Expand shell variables of form $var and ${var}.    Unknown variables are left unchanged."""    if '$' not in path:        return path    import string    varchars = string.ascii_letters + string.digits + '_-'    res = ''    index = 0    pathlen = len(path)    while index < pathlen:        c = path[index]        if c == '\'':   # no expansion within single quotes            path = path[index + 1:]            pathlen = len(path)            try:                index = path.index('\'')                res = res + '\'' + path[:index + 1]            except ValueError:                res = res + path                index = pathlen - 1        elif c == '$':  # variable or '$$'            if path[index + 1:index + 2] == '$':                res = res + c                index = index + 1            elif path[index + 1:index + 2] == '{':                path = path[index+2:]                pathlen = len(path)                try:                    index = path.index('}')                    var = path[:index]                    if var in os.environ:                        res = res + os.environ[var]                except ValueError:                    res = res + path                    index = pathlen - 1            else:                var = ''                index = index + 1                c = path[index:index + 1]                while c != '' and c in varchars:                    var = var + c                    index = index + 1                    c = path[index:index + 1]                if var in os.environ:                    res = res + os.environ[var]                if c != '':                    res = res + c        else:            res = res + c        index = index + 1    return res# Normalize a path, e.g. A//B, A/./B and A/foo/../B all become A\B.# Previously, this function also truncated pathnames to 8+3 format,# but as this module is called "ntpath", that's obviously wrong!def normpath(path):    """Normalize path, eliminating double slashes, etc."""    path = path.replace("/", "\\")    prefix, path = splitdrive(path)    # We need to be careful here. If the prefix is empty, and the path starts    # with a backslash, it could either be an absolute path on the current    # drive (\dir1\dir2\file) or a UNC filename (\\server\mount\dir1\file). It    # is therefore imperative NOT to collapse multiple backslashes blindly in    # that case.    # The code below preserves multiple backslashes when there is no drive    # letter. This means that the invalid filename \\\a\b is preserved    # unchanged, where a\\\b is normalised to a\b. It's not clear that there    # is any better behaviour for such edge cases.    if prefix == '':        # No drive letter - preserve initial backslashes        while path[:1] == "\\":            prefix = prefix + "\\"            path = path[1:]    else:        # We have a drive letter - collapse initial backslashes        if path.startswith("\\"):            prefix = prefix + "\\"            path = path.lstrip("\\")    comps = path.split("\\")    i = 0    while i < len(comps):        if comps[i] in ('.', ''):            del comps[i]        elif comps[i] == '..':            if i > 0 and comps[i-1] != '..':                del comps[i-1:i+1]                i -= 1            elif i == 0 and prefix.endswith("\\"):                del comps[i]            else:                i += 1        else:            i += 1    # If the path is now empty, substitute '.'    if not prefix and not comps:        comps.append('.')    return prefix + "\\".join(comps)# Return an absolute path.try:    from nt import _getfullpathnameexcept ImportError: # not running on Windows - mock up something sensible    def abspath(path):        """Return the absolute version of a path."""        if not isabs(path):            path = join(os.getcwd(), path)        return normpath(path)else:  # use native Windows method on Windows    def abspath(path):        """Return the absolute version of a path."""        if path: # Empty path must return current working directory.            try:                path = _getfullpathname(path)            except WindowsError:                pass # Bad path - return unchanged.        else:            path = os.getcwd()        return normpath(path)# realpath is a no-op on systems without islink supportrealpath = abspath# Win9x family and earlier have no Unicode filename support.supports_unicode_filenames = (hasattr(sys, "getwindowsversion") and                              sys.getwindowsversion()[3] >= 2)