home/diploma/lws_root/utils/path.py

""" path.py - An object representing a path to a file or directory.

Example:

from path import path
d = path('/home/guido/bin')
for f in d.files('*.py'):
    f.chmod(0755)

This module requires Python 2.2 or later.


URL:     http://www.jorendorff.com/articles/python/path
Author:  Jason Orendorff <jason.orendorff\x40gmail\x2ecom> (and others - see the url!)
Date:    7 Mar 2004
"""


# TODO
#   - Tree-walking functions don't avoid symlink loops.  Matt Harrison sent me a patch for this.
#   - Tree-walking functions can't ignore errors.  Matt Harrison asked for this.
#
#   - Two people asked for path.chdir().  This just seems wrong to me,
#     I dunno.  chdir() is moderately evil anyway.
#
#   - Bug in write_text().  It doesn't support Universal newline mode.
#   - Better error message in listdir() when self isn't a
#     directory. (On Windows, the error message really sucks.)
#   - Make sure everything has a good docstring.
#   - Add methods for regex find and replace.
#   - guess_content_type() method?
#   - Perhaps support arguments to touch().
#   - Could add split() and join() methods that generate warnings.

from __future__ import generators

import sys, warnings, os, fnmatch, glob, shutil, codecs, hashlib

__version__ = '2.1'
__all__ = ['path']

# Platform-specific support for path.owner
if os.name == 'nt':
    try:
        import win32security
    except ImportError:
        win32security = None
else:
    try:
        import pwd
    except ImportError:
        pwd = None

# Pre-2.3 support.  Are unicode filenames supported?
_base = str
_getcwd = os.getcwd
try:
    if os.path.supports_unicode_filenames:
        _base = unicode
        _getcwd = os.getcwdu
except AttributeError:
    pass

# Pre-2.3 workaround for booleans
try:
    True, False
except NameError:
    True, False = 1, 0

# Pre-2.3 workaround for basestring.
try:
    basestring
except NameError:
    basestring = (str, unicode)

# Universal newline support
_textmode = 'r'
if hasattr(file, 'newlines'):
    _textmode = 'U'


class TreeWalkWarning(Warning):
    pass

class path(_base):
    """ Represents a filesystem path.

    For documentation on individual methods, consult their
    counterparts in os.path.
    """

    # --- Special Python methods.

    def __repr__(self):
        return 'path(%s)' % _base.__repr__(_base(self))

    # Adding a path and a string yields a path.
    def __add__(self, more):
        try:
            resultStr = _base.__add__(self, more)
        except TypeError:  #Python bug
            resultStr = NotImplemented
        if resultStr is NotImplemented:
            return resultStr
        return self.__class__(resultStr)

    def __radd__(self, other):
        if isinstance(other, basestring):
            return self.__class__(other.__add__(self))
        else:
            return NotImplemented

    # The / operator joins paths.
    def __div__(self, rel):
        """ fp.__div__(rel) == fp / rel == fp.joinpath(rel)

        Join two path components, adding a separator character if
        needed.
        """
        return self.__class__(os.path.join(self, rel))

    # Make the / operator work even when true division is enabled.
    __truediv__ = __div__

    def getcwd(cls):
        """ Return the current working directory as a path object. """
        return cls(_getcwd())
    getcwd = classmethod(getcwd)


    # --- Operations on path strings.

    isabs = os.path.isabs
    def abspath(self):       return self.__class__(os.path.abspath(self))
    def normcase(self):      return self.__class__(os.path.normcase(self))
    def normpath(self):      return self.__class__(os.path.normpath(self))
    def realpath(self):      return self.__class__(os.path.realpath(self))
    def expanduser(self):    return self.__class__(os.path.expanduser(self))
    def expandvars(self):    return self.__class__(os.path.expandvars(self))
    def dirname(self):       return self.__class__(os.path.dirname(self))
    basename = os.path.basename

    def expand(self):
        """ Clean up a filename by calling expandvars(),
        expanduser(), and normpath() on it.

        This is commonly everything needed to clean up a filename
        read from a configuration file, for example.
        """
        return self.expandvars().expanduser().normpath()

    def _get_namebase(self):
        base, ext = os.path.splitext(self.name)
        return base

    def _get_ext(self):
        f, ext = os.path.splitext(_base(self))
        return ext

    def _get_drive(self):
        drive, r = os.path.splitdrive(self)
        return self.__class__(drive)

    parent = property(
        dirname, None, None,
        """ This path's parent directory, as a new path object.

        For example, path('/usr/local/lib/libpython.so').parent == path('/usr/local/lib')
        """)

    name = property(
        basename, None, None,
        """ The name of this file or directory without the full path.

        For example, path('/usr/local/lib/libpython.so').name == 'libpython.so'
        """)

    namebase = property(
        _get_namebase, None, None,
        """ The same as path.name, but with one file extension stripped off.

        For example, path('/home/guido/python.tar.gz').name     == 'python.tar.gz',
        but          path('/home/guido/python.tar.gz').namebase == 'python.tar'
        """)

    ext = property(
        _get_ext, None, None,
        """ The file extension, for example '.py'. """)

    drive = property(
        _get_drive, None, None,
        """ The drive specifier, for example 'C:'.
        This is always empty on systems that don't use drive specifiers.
        """)

    def splitpath(self):
        """ p.splitpath() -> Return (p.parent, p.name). """
        parent, child = os.path.split(self)
        return self.__class__(parent), child

    def splitdrive(self):
        """ p.splitdrive() -> Return (p.drive, <the rest of p>).

        Split the drive specifier from this path.  If there is
        no drive specifier, p.drive is empty, so the return value
        is simply (path(''), p).  This is always the case on Unix.
        """
        drive, rel = os.path.splitdrive(self)
        return self.__class__(drive), rel

    def splitext(self):
        """ p.splitext() -> Return (p.stripext(), p.ext).

        Split the filename extension from this path and return
        the two parts.  Either part may be empty.

        The extension is everything from '.' to the end of the
        last path segment.  This has the property that if
        (a, b) == p.splitext(), then a + b == p.
        """
        filename, ext = os.path.splitext(self)
        return self.__class__(filename), ext

    def stripext(self):
        """ p.stripext() -> Remove one file extension from the path.

        For example, path('/home/guido/python.tar.gz').stripext()
        returns path('/home/guido/python.tar').
        """
        return self.splitext()[0]

    if hasattr(os.path, 'splitunc'):
        def splitunc(self):
            unc, rest = os.path.splitunc(self)
            return self.__class__(unc), rest

        def _get_uncshare(self):
            unc, r = os.path.splitunc(self)
            return self.__class__(unc)

        uncshare = property(
            _get_uncshare, None, None,
            """ The UNC mount point for this path.
            This is empty for paths on local drives. """)

    def joinpath(self, *args):
        """ Join two or more path components, adding a separator
        character (os.sep) if needed.  Returns a new path
        object.
        """
        return self.__class__(os.path.join(self, *args))

    def splitall(self):
        r""" Return a list of the path components in this path.

        The first item in the list will be a path.  Its value will be
        either os.curdir, os.pardir, empty, or the root directory of
        this path (for example, '/' or 'C:\\').  The other items in
        the list will be strings.

        path.path.joinpath(*result) will yield the original path.
        """
        parts = []
        loc = self
        while loc != os.curdir and loc != os.pardir:
            prev = loc
            loc, child = prev.splitpath()
            if loc == prev:
                break
            parts.append(child)
        parts.append(loc)
        parts.reverse()
        return parts

    def relpath(self):
        """ Return this path as a relative path,
        based from the current working directory.
        """
        cwd = self.__class__(os.getcwd())
        return cwd.relpathto(self)

    def relpathto(self, dest):
        """ Return a relative path from self to dest.

        If there is no relative path from self to dest, for example if
        they reside on different drives in Windows, then this returns
        dest.abspath().
        """
        origin = self.abspath()
        dest = self.__class__(dest).abspath()

        orig_list = origin.normcase().splitall()
        # Don't normcase dest!  We want to preserve the case.
        dest_list = dest.splitall()

        if orig_list[0] != os.path.normcase(dest_list[0]):
            # Can't get here from there.
            return dest

        # Find the location where the two paths start to differ.
        i = 0
        for start_seg, dest_seg in zip(orig_list, dest_list):
            if start_seg != os.path.normcase(dest_seg):
                break
            i += 1

        # Now i is the point where the two paths diverge.
        # Need a certain number of "os.pardir"s to work up
        # from the origin to the point of divergence.
        segments = [os.pardir] * (len(orig_list) - i)
        # Need to add the diverging part of dest_list.
        segments += dest_list[i:]
        if len(segments) == 0:
            # If they happen to be identical, use os.curdir.
            relpath = os.curdir
        else:
            relpath = os.path.join(*segments)
        return self.__class__(relpath)

    # --- Listing, searching, walking, and matching

    def listdir(self, pattern=None):
        """ D.listdir() -> List of items in this directory.

        Use D.files() or D.dirs() instead if you want a listing
        of just files or just subdirectories.

        The elements of the list are path objects.

        With the optional 'pattern' argument, this only lists
        items whose names match the given pattern.
        """
        names = os.listdir(self)
        if pattern is not None:
            names = fnmatch.filter(names, pattern)
        return [self / child for child in names]

    def dirs(self, pattern=None):
        """ D.dirs() -> List of this directory's subdirectories.

        The elements of the list are path objects.
        This does not walk recursively into subdirectories
        (but see path.walkdirs).

        With the optional 'pattern' argument, this only lists
        directories whose names match the given pattern.  For
        example, d.dirs('build-*').
        """
        return [p for p in self.listdir(pattern) if p.isdir()]

    def files(self, pattern=None):
        """ D.files() -> List of the files in this directory.

        The elements of the list are path objects.
        This does not walk into subdirectories (see path.walkfiles).

        With the optional 'pattern' argument, this only lists files
        whose names match the given pattern.  For example,
        d.files('*.pyc').
        """
        
        return [p for p in self.listdir(pattern) if p.isfile()]

    def walk(self, pattern=None, errors='strict'):
        """ D.walk() -> iterator over files and subdirs, recursively.

        The iterator yields path objects naming each child item of
        this directory and its descendants.  This requires that
        D.isdir().

        This performs a depth-first traversal of the directory tree.
        Each directory is returned just before all its children.

        The errors= keyword argument controls behavior when an
        error occurs.  The default is 'strict', which causes an
        exception.  The other allowed values are 'warn', which
        reports the error via warnings.warn(), and 'ignore'.
        """
        if errors not in ('strict', 'warn', 'ignore'):
            raise ValueError("invalid errors parameter")

        try:
            childList = self.listdir()
        except Exception:
            if errors == 'ignore':
                return
            elif errors == 'warn':
                warnings.warn(
                    "Unable to list directory '%s': %s"
                    % (self, sys.exc_info()[1]),
                    TreeWalkWarning)
            else:
                raise

        for child in childList:
            if pattern is None or child.fnmatch(pattern):
                yield child
            try:
                isdir = child.isdir()
            except Exception:
                if errors == 'ignore':
                    isdir = False
                elif errors == 'warn':
                    warnings.warn(
                        "Unable to access '%s': %s"
                        % (child, sys.exc_info()[1]),
                        TreeWalkWarning)
                    isdir = False
                else:
                    raise

            if isdir:
                for item in child.walk(pattern, errors):
                    yield item

    def walkdirs(self, pattern=None, errors='strict'):
        """ D.walkdirs() -> iterator over subdirs, recursively.

        With the optional 'pattern' argument, this yields only
        directories whose names match the given pattern.  For
        example, mydir.walkdirs('*test') yields only directories
        with names ending in 'test'.

        The errors= keyword argument controls behavior when an
        error occurs.  The default is 'strict', which causes an
        exception.  The other allowed values are 'warn', which
        reports the error via warnings.warn(), and 'ignore'.
        """
        if errors not in ('strict', 'warn', 'ignore'):
            raise ValueError("invalid errors parameter")

        try:
            dirs = self.dirs()
        except Exception:
            if errors == 'ignore':
                return
            elif errors == 'warn':
                warnings.warn(
                    "Unable to list directory '%s': %s"
                    % (self, sys.exc_info()[1]),
                    TreeWalkWarning)
            else:
                raise

        for child in dirs:
            if pattern is None or child.fnmatch(pattern):
                yield child
            for subsubdir in child.walkdirs(pattern, errors):
                yield subsubdir

    def walkfiles(self, pattern=None, errors='strict'):
        """ D.walkfiles() -> iterator over files in D, recursively.

        The optional argument, pattern, limits the results to files
        with names that match the pattern.  For example,
        mydir.walkfiles('*.tmp') yields only files with the .tmp
        extension.
        """
        if errors not in ('strict', 'warn', 'ignore'):
            raise ValueError("invalid errors parameter")

        try:
            childList = self.listdir()
        except Exception:
            if errors == 'ignore':
                return
            elif errors == 'warn':
                warnings.warn(
                    "Unable to list directory '%s': %s"
                    % (self, sys.exc_info()[1]),
                    TreeWalkWarning)
            else:
                raise

        for child in childList:
            try:
                isfile = child.isfile()
                isdir = not isfile and child.isdir()
            except:
                if errors == 'ignore':
                    return
                elif errors == 'warn':
                    warnings.warn(
                        "Unable to access '%s': %s"
                        % (self, sys.exc_info()[1]),
                        TreeWalkWarning)
                else:
                    raise

            if isfile:
                if pattern is None or child.fnmatch(pattern):
                    yield child
            elif isdir:
                for f in child.walkfiles(pattern, errors):
                    yield f

    def fnmatch(self, pattern):
        """ Return True if self.name matches the given pattern.

        pattern - A filename pattern with wildcards,
            for example '*.py'.
        """
        return fnmatch.fnmatch(self.name, pattern)

    def glob(self, pattern):
        """ Return a list of path objects that match the pattern.

        pattern - a path relative to this directory, with wildcards.

        For example, path('/users').glob('*/bin/*') returns a list
        of all the files users have in their bin directories.
        """
        cls = self.__class__
        return [cls(s) for s in glob.glob(_base(self / pattern))]


    # --- Reading or writing an entire file at once.

    def open(self, mode='r'):
        """ Open this file.  Return a file object. """
        return file(self, mode)

    def bytes(self):
        """ Open this file, read all bytes, return them as a string. """
        f = self.open('rb')
        try:
            return f.read()
        finally:
            f.close()

    def write_bytes(self, bytes, append=False):
        """ Open this file and write the given bytes to it.

        Default behavior is to overwrite any existing file.
        Call p.write_bytes(bytes, append=True) to append instead.
        """
        if append:
            mode = 'ab'
        else:
            mode = 'wb'
        f = self.open(mode)
        try:
            f.write(bytes)
        finally:
            f.close()

    def text(self, encoding=None, errors='strict'):
        r""" Open this file, read it in, return the content as a string.

        This uses 'U' mode in Python 2.3 and later, so '\r\n' and '\r'
        are automatically translated to '\n'.

        Optional arguments:

        encoding - The Unicode encoding (or character set) of
            the file.  If present, the content of the file is
            decoded and returned as a unicode object; otherwise
            it is returned as an 8-bit str.
        errors - How to handle Unicode errors; see help(str.decode)
            for the options.  Default is 'strict'.
        """
        if encoding is None:
            # 8-bit
            f = self.open(_textmode)
            try:
                return f.read()
            finally:
                f.close()
        else:
            # Unicode
            f = codecs.open(self, 'r', encoding, errors)
            # (Note - Can't use 'U' mode here, since codecs.open
            # doesn't support 'U' mode, even in Python 2.3.)
            try:
                t = f.read()
            finally:
                f.close()
            return (t.replace(u'\r\n', u'\n')
                     .replace(u'\r\x85', u'\n')
                     .replace(u'\r', u'\n')
                     .replace(u'\x85', u'\n')
                     .replace(u'\u2028', u'\n'))

    def write_text(self, text, encoding=None, errors='strict', linesep=os.linesep, append=False):
        r""" Write the given text to this file.

        The default behavior is to overwrite any existing file;
        to append instead, use the 'append=True' keyword argument.

        There are two differences between path.write_text() and
        path.write_bytes(): newline handling and Unicode handling.
        See below.

        Parameters:

          - text - str/unicode - The text to be written.

          - encoding - str - The Unicode encoding that will be used.
            This is ignored if 'text' isn't a Unicode string.

          - errors - str - How to handle Unicode encoding errors.
            Default is 'strict'.  See help(unicode.encode) for the
            options.  This is ignored if 'text' isn't a Unicode
            string.

          - linesep - keyword argument - str/unicode - The sequence of
            characters to be used to mark end-of-line.  The default is
            os.linesep.  You can also specify None; this means to
            leave all newlines as they are in 'text'.

          - append - keyword argument - bool - Specifies what to do if
            the file already exists (True: append to the end of it;
            False: overwrite it.)  The default is False.


        --- Newline handling.

        write_text() converts all standard end-of-line sequences
        ('\n', '\r', and '\r\n') to your platform's default end-of-line
        sequence (see os.linesep; on Windows, for example, the
        end-of-line marker is '\r\n').

        If you don't like your platform's default, you can override it
        using the 'linesep=' keyword argument.  If you specifically want
        write_text() to preserve the newlines as-is, use 'linesep=None'.

        This applies to Unicode text the same as to 8-bit text, except
        there are three additional standard Unicode end-of-line sequences:
        u'\x85', u'\r\x85', and u'\u2028'.

        (This is slightly different from when you open a file for
        writing with fopen(filename, "w") in C or file(filename, 'w')
        in Python.)


        --- Unicode

        If 'text' isn't Unicode, then apart from newline handling, the
        bytes are written verbatim to the file.  The 'encoding' and
        'errors' arguments are not used and must be omitted.

        If 'text' is Unicode, it is first converted to bytes using the
        specified 'encoding' (or the default encoding if 'encoding'
        isn't specified).  The 'errors' argument applies only to this
        conversion.

        """
        if isinstance(text, unicode):
            if linesep is not None:
                # Convert all standard end-of-line sequences to
                # ordinary newline characters.
                text = (text.replace(u'\r\n', u'\n')
                            .replace(u'\r\x85', u'\n')
                            .replace(u'\r', u'\n')
                            .replace(u'\x85', u'\n')
                            .replace(u'\u2028', u'\n'))
                text = text.replace(u'\n', linesep)
            if encoding is None:
                encoding = sys.getdefaultencoding()
            bytes = text.encode(encoding, errors)
        else:
            # It is an error to specify an encoding if 'text' is
            # an 8-bit string.
            assert encoding is None

            if linesep is not None:
                text = (text.replace('\r\n', '\n')
                            .replace('\r', '\n'))
                bytes = text.replace('\n', linesep)

        self.write_bytes(bytes, append)

    def lines(self, encoding=None, errors='strict', retain=True):
        r""" Open this file, read all lines, return them in a list.

        Optional arguments:
            encoding - The Unicode encoding (or character set) of
                the file.  The default is None, meaning the content
                of the file is read as 8-bit characters and returned
                as a list of (non-Unicode) str objects.
            errors - How to handle Unicode errors; see help(str.decode)
                for the options.  Default is 'strict'
            retain - If true, retain newline characters; but all newline
                character combinations ('\r', '\n', '\r\n') are
                translated to '\n'.  If false, newline characters are
                stripped off.  Default is True.

        This uses 'U' mode in Python 2.3 and later.
        """
        if encoding is None and retain:
            f = self.open(_textmode)
            try:
                return f.readlines()
            finally:
                f.close()
        else:
            return self.text(encoding, errors).splitlines(retain)

    def write_lines(self, lines, encoding=None, errors='strict',
                    linesep=os.linesep, append=False):
        r""" Write the given lines of text to this file.

        By default this overwrites any existing file at this path.

        This puts a platform-specific newline sequence on every line.
        See 'linesep' below.

        lines - A list of strings.

        encoding - A Unicode encoding to use.  This applies only if
            'lines' contains any Unicode strings.

        errors - How to handle errors in Unicode encoding.  This
            also applies only to Unicode strings.

        linesep - The desired line-ending.  This line-ending is
            applied to every line.  If a line already has any
            standard line ending ('\r', '\n', '\r\n', u'\x85',
            u'\r\x85', u'\u2028'), that will be stripped off and
            this will be used instead.  The default is os.linesep,
            which is platform-dependent ('\r\n' on Windows, '\n' on
            Unix, etc.)  Specify None to write the lines as-is,
            like file.writelines().

        Use the keyword argument append=True to append lines to the
        file.  The default is to overwrite the file.  Warning:
        When you use this with Unicode data, if the encoding of the
        existing data in the file is different from the encoding
        you specify with the encoding= parameter, the result is
        mixed-encoding data, which can really confuse someone trying
        to read the file later.
        """
        if append:
            mode = 'ab'
        else:
            mode = 'wb'
        f = self.open(mode)
        try:
            for line in lines:
                isUnicode = isinstance(line, unicode)
                if linesep is not None:
                    # Strip off any existing line-end and add the
                    # specified linesep string.
                    if isUnicode:
                        if line[-2:] in (u'\r\n', u'\x0d\x85'):
                            line = line[:-2]
                        elif line[-1:] in (u'\r', u'\n',
                                           u'\x85', u'\u2028'):
                            line = line[:-1]
                    else:
                        if line[-2:] == '\r\n':
                            line = line[:-2]
                        elif line[-1:] in ('\r', '\n'):
                            line = line[:-1]
                    line += linesep
                if isUnicode:
                    if encoding is None:
                        encoding = sys.getdefaultencoding()
                    line = line.encode(encoding, errors)
                f.write(line)
        finally:
            f.close()

    def read_md5(self):
        """ Calculate the md5 hash for this file.

        This reads through the entire file.
        """
        f = self.open('rb')
        try:
            m = hashlib.md5()
            while True:
                d = f.read(8192)
                if not d:
                    break
                m.update(d)
        finally:
            f.close()
        return m.digest()

    # --- Methods for querying the filesystem.

    exists = os.path.exists
    isdir = os.path.isdir
    isfile = os.path.isfile
    islink = os.path.islink
    ismount = os.path.ismount

    if hasattr(os.path, 'samefile'):
        samefile = os.path.samefile

    getatime = os.path.getatime
    atime = property(
        getatime, None, None,
        """ Last access time of the file. """)

    getmtime = os.path.getmtime
    mtime = property(
        getmtime, None, None,
        """ Last-modified time of the file. """)

    if hasattr(os.path, 'getctime'):
        getctime = os.path.getctime
        ctime = property(
            getctime, None, None,
            """ Creation time of the file. """)

    getsize = os.path.getsize
    size = property(
        getsize, None, None,
        """ Size of the file, in bytes. """)

    if hasattr(os, 'access'):
        def access(self, mode):
            """ Return true if current user has access to this path.

            mode - One of the constants os.F_OK, os.R_OK, os.W_OK, os.X_OK
            """
            return os.access(self, mode)

    def stat(self):
        """ Perform a stat() system call on this path. """
        return os.stat(self)

    def lstat(self):
        """ Like path.stat(), but do not follow symbolic links. """
        return os.lstat(self)

    def get_owner(self):
        r""" Return the name of the owner of this file or directory.

        This follows symbolic links.

        On Windows, this returns a name of the form ur'DOMAIN\User Name'.
        On Windows, a group can own a file or directory.
        """
        if os.name == 'nt':
            if win32security is None:
                raise Exception("path.owner requires win32all to be installed")
            desc = win32security.GetFileSecurity(
                self, win32security.OWNER_SECURITY_INFORMATION)
            sid = desc.GetSecurityDescriptorOwner()
            account, domain, typecode = win32security.LookupAccountSid(None, sid)
            return domain + u'\\' + account
        else:
            if pwd is None:
                raise NotImplementedError("path.owner is not implemented on this platform.")
            st = self.stat()
            return pwd.getpwuid(st.st_uid).pw_name

    owner = property(
        get_owner, None, None,
        """ Name of the owner of this file or directory. """)

    if hasattr(os, 'statvfs'):
        def statvfs(self):
            """ Perform a statvfs() system call on this path. """
            return os.statvfs(self)

    if hasattr(os, 'pathconf'):
        def pathconf(self, name):
            return os.pathconf(self, name)


    # --- Modifying operations on files and directories

    def utime(self, times):
        """ Set the access and modified times of this file. """
        os.utime(self, times)

    def chmod(self, mode):
        os.chmod(self, mode)

    if hasattr(os, 'chown'):
        def chown(self, uid, gid):
            os.chown(self, uid, gid)

    def rename(self, new):
        os.rename(self, new)

    def renames(self, new):
        os.renames(self, new)


    # --- Create/delete operations on directories

    def mkdir(self, mode=0777):
        os.mkdir(self, mode)

    def makedirs(self, mode=0777):
        os.makedirs(self, mode)

    def rmdir(self):
        os.rmdir(self)

    def removedirs(self):
        os.removedirs(self)


    # --- Modifying operations on files

    def touch(self):
        """ Set the access/modified times of this file to the current time.
        Create the file if it does not exist.
        """
        fd = os.open(self, os.O_WRONLY | os.O_CREAT, 0666)
        os.close(fd)
        os.utime(self, None)

    def remove(self):
        os.remove(self)

    def unlink(self):
        os.unlink(self)


    # --- Links

    if hasattr(os, 'link'):
        def link(self, newpath):
            """ Create a hard link at 'newpath', pointing to this file. """
            os.link(self, newpath)

    if hasattr(os, 'symlink'):
        def symlink(self, newlink):
            """ Create a symbolic link at 'newlink', pointing here. """
            os.symlink(self, newlink)

    if hasattr(os, 'readlink'):
        def readlink(self):
            """ Return the path to which this symbolic link points.

            The result may be an absolute or a relative path.
            """
            return self.__class__(os.readlink(self))

        def readlinkabs(self):
            """ Return the path to which this symbolic link points.

            The result is always an absolute path.
            """
            p = self.readlink()
            if p.isabs():
                return p
            else:
                return (self.parent / p).abspath()


    # --- High-level functions from shutil

    copyfile = shutil.copyfile
    copymode = shutil.copymode
    copystat = shutil.copystat
    copy = shutil.copy
    copy2 = shutil.copy2
    copytree = shutil.copytree
    if hasattr(shutil, 'move'):
        move = shutil.move
    rmtree = shutil.rmtree


    # --- Special stuff from os

    if hasattr(os, 'chroot'):
        def chroot(self):
            os.chroot(self)

    if hasattr(os, 'startfile'):
        def startfile(self):
            os.startfile(self)