python模块：shutil

 """Utility functions for copying and archiving files and directory trees.

 XXX The functions here don't copy the resource fork or other metadata on Mac.

 """

 import os
 import sys
 import stat
 import fnmatch
 import collections
 import errno

 try:
     import zlib
     del zlib
     _ZLIB_SUPPORTED = True
 except ImportError:
     _ZLIB_SUPPORTED = False

 try:
     import bz2
     del bz2
     _BZ2_SUPPORTED = True
 except ImportError:
     _BZ2_SUPPORTED = False

 try:
     import lzma
     del lzma
     _LZMA_SUPPORTED = True
 except ImportError:
     _LZMA_SUPPORTED = False

 try:
     from pwd import getpwnam
 except ImportError:
     getpwnam = None

 try:
     from grp import getgrnam
 except ImportError:
     getgrnam = None

 __all__ = ["copyfileobj", "copyfile", "copymode", "copystat", "copy", "copy2",
            "copytree", "move", "rmtree", "Error", "SpecialFileError",
            "ExecError", "make_archive", "get_archive_formats",
            "register_archive_format", "unregister_archive_format",
            "get_unpack_formats", "register_unpack_format",
            "unregister_unpack_format", "unpack_archive",
            "ignore_patterns", "chown", "which", "get_terminal_size",
            "SameFileError"]
            # disk_usage is added later, if available on the platform

 class Error(OSError):
     pass

 class SameFileError(Error):
     """Raised when source and destination are the same file."""

 class SpecialFileError(OSError):
     """Raised when trying to do a kind of operation (e.g. copying) which is
     not supported on a special file (e.g. a named pipe)"""

 class ExecError(OSError):
     """Raised when a command could not be executed"""

 class ReadError(OSError):
     """Raised when an archive cannot be read"""

 class RegistryError(Exception):
     """Raised when a registry operation with the archiving
     and unpacking registries fails"""

 def copyfileobj(fsrc, fdst, length=16*1024):
     """copy data from file-like object fsrc to file-like object fdst"""
     while 1:
         buf = fsrc.read(length)
         if not buf:
             break
         fdst.write(buf)

 def _samefile(src, dst):
     # Macintosh, Unix.
     if hasattr(os.path, 'samefile'):
         try:
             return os.path.samefile(src, dst)
         except OSError:
             return False

     # All other platforms: check for same pathname.
     return (os.path.normcase(os.path.abspath(src)) ==
             os.path.normcase(os.path.abspath(dst)))

 def copyfile(src, dst, *, follow_symlinks=True):
     """Copy data from src to dst.

     If follow_symlinks is not set and src is a symbolic link, a new
     symlink will be created instead of copying the file it points to.

     """
     if _samefile(src, dst):
         raise SameFileError("{!r} and {!r} are the same file".format(src, dst))

     for fn in [src, dst]:
         try:
             st = os.stat(fn)
         except OSError:
             # File most likely does not exist
             pass
         else:
             # XXX What about other special files? (sockets, devices...)
             if stat.S_ISFIFO(st.st_mode):
                 raise SpecialFileError("`%s` is a named pipe" % fn)

     if not follow_symlinks and os.path.islink(src):
         os.symlink(os.readlink(src), dst)
     else:
         with open(src, 'rb') as fsrc:
             with open(dst, 'wb') as fdst:
                 copyfileobj(fsrc, fdst)
     return dst

 def copymode(src, dst, *, follow_symlinks=True):
     """Copy mode bits from src to dst.

     If follow_symlinks is not set, symlinks aren't followed if and only
     if both `src` and `dst` are symlinks.  If `lchmod` isn't available
     (e.g. Linux) this method does nothing.

     """
     if not follow_symlinks and os.path.islink(src) and os.path.islink(dst):
         if hasattr(os, 'lchmod'):
             stat_func, chmod_func = os.lstat, os.lchmod
         else:
             return
     elif hasattr(os, 'chmod'):
         stat_func, chmod_func = os.stat, os.chmod
     else:
         return

     st = stat_func(src)
     chmod_func(dst, stat.S_IMODE(st.st_mode))

 if hasattr(os, 'listxattr'):
     def _copyxattr(src, dst, *, follow_symlinks=True):
         """Copy extended filesystem attributes from `src` to `dst`.

         Overwrite existing attributes.

         If `follow_symlinks` is false, symlinks won't be followed.

         """

         try:
             names = os.listxattr(src, follow_symlinks=follow_symlinks)
         except OSError as e:
             if e.errno not in (errno.ENOTSUP, errno.ENODATA):
                 raise
             return
         for name in names:
             try:
                 value = os.getxattr(src, name, follow_symlinks=follow_symlinks)
                 os.setxattr(dst, name, value, follow_symlinks=follow_symlinks)
             except OSError as e:
                 if e.errno not in (errno.EPERM, errno.ENOTSUP, errno.ENODATA):
                     raise
 else:
     def _copyxattr(*args, **kwargs):
         pass

 def copystat(src, dst, *, follow_symlinks=True):
     """Copy all stat info (mode bits, atime, mtime, flags) from src to dst.

     If the optional flag `follow_symlinks` is not set, symlinks aren't followed if and
     only if both `src` and `dst` are symlinks.

     """
     def _nop(*args, ns=None, follow_symlinks=None):
         pass

     # follow symlinks (aka don't not follow symlinks)
     follow = follow_symlinks or not (os.path.islink(src) and os.path.islink(dst))
     if follow:
         # use the real function if it exists
         def lookup(name):
             return getattr(os, name, _nop)
     else:
         # use the real function only if it exists
         # *and* it supports follow_symlinks
         def lookup(name):
             fn = getattr(os, name, _nop)
             if fn in os.supports_follow_symlinks:
                 return fn
             return _nop

     st = lookup("stat")(src, follow_symlinks=follow)
     mode = stat.S_IMODE(st.st_mode)
     lookup("utime")(dst, ns=(st.st_atime_ns, st.st_mtime_ns),
         follow_symlinks=follow)
     try:
         lookup("chmod")(dst, mode, follow_symlinks=follow)
     except NotImplementedError:
         # if we got a NotImplementedError, it's because
         #   * follow_symlinks=False,
         #   * lchown() is unavailable, and
         #   * either
         #       * fchownat() is unavailable or
         #       * fchownat() doesn't implement AT_SYMLINK_NOFOLLOW.
         #         (it returned ENOSUP.)
         # therefore we're out of options--we simply cannot chown the
         # symlink.  give up, suppress the error.
         # (which is what shutil always did in this circumstance.)
         pass
     if hasattr(st, 'st_flags'):
         try:
             lookup("chflags")(dst, st.st_flags, follow_symlinks=follow)
         except OSError as why:
             for err in 'EOPNOTSUPP', 'ENOTSUP':
                 if hasattr(errno, err) and why.errno == getattr(errno, err):
                     break
             else:
                 raise
     _copyxattr(src, dst, follow_symlinks=follow)

 def copy(src, dst, *, follow_symlinks=True):
     """Copy data and mode bits ("cp src dst"). Return the file's destination.

     The destination may be a directory.

     If follow_symlinks is false, symlinks won't be followed. This
     resembles GNU's "cp -P src dst".

     If source and destination are the same file, a SameFileError will be
     raised.

     """
     if os.path.isdir(dst):
         dst = os.path.join(dst, os.path.basename(src))
     copyfile(src, dst, follow_symlinks=follow_symlinks)
     copymode(src, dst, follow_symlinks=follow_symlinks)
     return dst

 def copy2(src, dst, *, follow_symlinks=True):
     """Copy data and all stat info ("cp -p src dst"). Return the file's
     destination."

     The destination may be a directory.

     If follow_symlinks is false, symlinks won't be followed. This
     resembles GNU's "cp -P src dst".

     """
     if os.path.isdir(dst):
         dst = os.path.join(dst, os.path.basename(src))
     copyfile(src, dst, follow_symlinks=follow_symlinks)
     copystat(src, dst, follow_symlinks=follow_symlinks)
     return dst

 def ignore_patterns(*patterns):
     """Function that can be used as copytree() ignore parameter.

     Patterns is a sequence of glob-style patterns
     that are used to exclude files"""
     def _ignore_patterns(path, names):
         ignored_names = []
         for pattern in patterns:
             ignored_names.extend(fnmatch.filter(names, pattern))
         return set(ignored_names)
     return _ignore_patterns

 def copytree(src, dst, symlinks=False, ignore=None, copy_function=copy2,
              ignore_dangling_symlinks=False):
     """Recursively copy a directory tree.

     The destination directory must not already exist.
     If exception(s) occur, an Error is raised with a list of reasons.

     If the optional symlinks flag is true, symbolic links in the
     source tree result in symbolic links in the destination tree; if
     it is false, the contents of the files pointed to by symbolic
     links are copied. If the file pointed by the symlink doesn't
     exist, an exception will be added in the list of errors raised in
     an Error exception at the end of the copy process.

     You can set the optional ignore_dangling_symlinks flag to true if you
     want to silence this exception. Notice that this has no effect on
     platforms that don't support os.symlink.

     The optional ignore argument is a callable. If given, it
     is called with the `src` parameter, which is the directory
     being visited by copytree(), and `names` which is the list of
     `src` contents, as returned by os.listdir():

         callable(src, names) -> ignored_names

     Since copytree() is called recursively, the callable will be
     called once for each directory that is copied. It returns a
     list of names relative to the `src` directory that should
     not be copied.

     The optional copy_function argument is a callable that will be used
     to copy each file. It will be called with the source path and the
     destination path as arguments. By default, copy2() is used, but any
     function that supports the same signature (like copy()) can be used.

     """
     names = os.listdir(src)
     if ignore is not None:
         ignored_names = ignore(src, names)
     else:
         ignored_names = set()

     os.makedirs(dst)
     errors = []
     for name in names:
         if name in ignored_names:
             continue
         srcname = os.path.join(src, name)
         dstname = os.path.join(dst, name)
         try:
             if os.path.islink(srcname):
                 linkto = os.readlink(srcname)
                 if symlinks:
                     # We can't just leave it to `copy_function` because legacy
                     # code with a custom `copy_function` may rely on copytree
                     # doing the right thing.
                     os.symlink(linkto, dstname)
                     copystat(srcname, dstname, follow_symlinks=not symlinks)
                 else:
                     # ignore dangling symlink if the flag is on
                     if not os.path.exists(linkto) and ignore_dangling_symlinks:
                         continue
                     # otherwise let the copy occurs. copy2 will raise an error
                     if os.path.isdir(srcname):
                         copytree(srcname, dstname, symlinks, ignore,
                                  copy_function)
                     else:
                         copy_function(srcname, dstname)
             elif os.path.isdir(srcname):
                 copytree(srcname, dstname, symlinks, ignore, copy_function)
             else:
                 # Will raise a SpecialFileError for unsupported file types
                 copy_function(srcname, dstname)
         # catch the Error from the recursive copytree so that we can
         # continue with other files
         except Error as err:
             errors.extend(err.args[0])
         except OSError as why:
             errors.append((srcname, dstname, str(why)))
     try:
         copystat(src, dst)
     except OSError as why:
         # Copying file access times may fail on Windows
         if getattr(why, 'winerror', None) is None:
             errors.append((src, dst, str(why)))
     if errors:
         raise Error(errors)
     return dst

 # version vulnerable to race conditions
 def _rmtree_unsafe(path, onerror):
     try:
         if os.path.islink(path):
             # symlinks to directories are forbidden, see bug #1669
             raise OSError("Cannot call rmtree on a symbolic link")
     except OSError:
         onerror(os.path.islink, path, sys.exc_info())
         # can't continue even if onerror hook returns
         return
     names = []
     try:
         names = os.listdir(path)
     except OSError:
         onerror(os.listdir, path, sys.exc_info())
     for name in names:
         fullname = os.path.join(path, name)
         try:
             mode = os.lstat(fullname).st_mode
         except OSError:
             mode = 0
         if stat.S_ISDIR(mode):
             _rmtree_unsafe(fullname, onerror)
         else:
             try:
                 os.unlink(fullname)
             except OSError:
                 onerror(os.unlink, fullname, sys.exc_info())
     try:
         os.rmdir(path)
     except OSError:
         onerror(os.rmdir, path, sys.exc_info())

 # Version using fd-based APIs to protect against races
 def _rmtree_safe_fd(topfd, path, onerror):
     names = []
     try:
         names = os.listdir(topfd)
     except OSError as err:
         err.filename = path
         onerror(os.listdir, path, sys.exc_info())
     for name in names:
         fullname = os.path.join(path, name)
         try:
             orig_st = os.stat(name, dir_fd=topfd, follow_symlinks=False)
             mode = orig_st.st_mode
         except OSError:
             mode = 0
         if stat.S_ISDIR(mode):
             try:
                 dirfd = os.open(name, os.O_RDONLY, dir_fd=topfd)
             except OSError:
                 onerror(os.open, fullname, sys.exc_info())
             else:
                 try:
                     if os.path.samestat(orig_st, os.fstat(dirfd)):
                         _rmtree_safe_fd(dirfd, fullname, onerror)
                         try:
                             os.rmdir(name, dir_fd=topfd)
                         except OSError:
                             onerror(os.rmdir, fullname, sys.exc_info())
                     else:
                         try:
                             # This can only happen if someone replaces
                             # a directory with a symlink after the call to
                             # stat.S_ISDIR above.
                             raise OSError("Cannot call rmtree on a symbolic "
                                           "link")
                         except OSError:
                             onerror(os.path.islink, fullname, sys.exc_info())
                 finally:
                     os.close(dirfd)
         else:
             try:
                 os.unlink(name, dir_fd=topfd)
             except OSError:
                 onerror(os.unlink, fullname, sys.exc_info())

 _use_fd_functions = ({os.open, os.stat, os.unlink, os.rmdir} <=
                      os.supports_dir_fd and
                      os.listdir in os.supports_fd and
                      os.stat in os.supports_follow_symlinks)

 def rmtree(path, ignore_errors=False, onerror=None):
     """Recursively delete a directory tree.

     If ignore_errors is set, errors are ignored; otherwise, if onerror
     is set, it is called to handle the error with arguments (func,
     path, exc_info) where func is platform and implementation dependent;
     path is the argument to that function that caused it to fail; and
     exc_info is a tuple returned by sys.exc_info().  If ignore_errors
     is false and onerror is None, an exception is raised.

     """
     if ignore_errors:
         def onerror(*args):
             pass
     elif onerror is None:
         def onerror(*args):
             raise
     if _use_fd_functions:
         # While the unsafe rmtree works fine on bytes, the fd based does not.
         if isinstance(path, bytes):
             path = os.fsdecode(path)
         # Note: To guard against symlink races, we use the standard
         # lstat()/open()/fstat() trick.
         try:
             orig_st = os.lstat(path)
         except Exception:
             onerror(os.lstat, path, sys.exc_info())
             return
         try:
             fd = os.open(path, os.O_RDONLY)
         except Exception:
             onerror(os.lstat, path, sys.exc_info())
             return
         try:
             if os.path.samestat(orig_st, os.fstat(fd)):
                 _rmtree_safe_fd(fd, path, onerror)
                 try:
                     os.rmdir(path)
                 except OSError:
                     onerror(os.rmdir, path, sys.exc_info())
             else:
                 try:
                     # symlinks to directories are forbidden, see bug #1669
                     raise OSError("Cannot call rmtree on a symbolic link")
                 except OSError:
                     onerror(os.path.islink, path, sys.exc_info())
         finally:
             os.close(fd)
     else:
         return _rmtree_unsafe(path, onerror)

 # Allow introspection of whether or not the hardening against symlink
 # attacks is supported on the current platform
 rmtree.avoids_symlink_attacks = _use_fd_functions

 def _basename(path):
     # A basename() variant which first strips the trailing slash, if present.
     # Thus we always get the last component of the path, even for directories.
     sep = os.path.sep + (os.path.altsep or '')
     return os.path.basename(path.rstrip(sep))

 def move(src, dst, copy_function=copy2):
     """Recursively move a file or directory to another location. This is
     similar to the Unix "mv" command. Return the file or directory's
     destination.

     If the destination is a directory or a symlink to a directory, the source
     is moved inside the directory. The destination path must not already
     exist.

     If the destination already exists but is not a directory, it may be
     overwritten depending on os.rename() semantics.

     If the destination is on our current filesystem, then rename() is used.
     Otherwise, src is copied to the destination and then removed. Symlinks are
     recreated under the new name if os.rename() fails because of cross
     filesystem renames.

     The optional `copy_function` argument is a callable that will be used
     to copy the source or it will be delegated to `copytree`.
     By default, copy2() is used, but any function that supports the same
     signature (like copy()) can be used.

     A lot more could be done here...  A look at a mv.c shows a lot of
     the issues this implementation glosses over.

     """
     real_dst = dst
     if os.path.isdir(dst):
         if _samefile(src, dst):
             # We might be on a case insensitive filesystem,
             # perform the rename anyway.
             os.rename(src, dst)
             return

         real_dst = os.path.join(dst, _basename(src))
         if os.path.exists(real_dst):
             raise Error("Destination path '%s' already exists" % real_dst)
     try:
         os.rename(src, real_dst)
     except OSError:
         if os.path.islink(src):
             linkto = os.readlink(src)
             os.symlink(linkto, real_dst)
             os.unlink(src)
         elif os.path.isdir(src):
             if _destinsrc(src, dst):
                 raise Error("Cannot move a directory '%s' into itself"
                             " '%s'." % (src, dst))
             copytree(src, real_dst, copy_function=copy_function,
                      symlinks=True)
             rmtree(src)
         else:
             copy_function(src, real_dst)
             os.unlink(src)
     return real_dst

 def _destinsrc(src, dst):
     src = os.path.abspath(src)
     dst = os.path.abspath(dst)
     if not src.endswith(os.path.sep):
         src += os.path.sep
     if not dst.endswith(os.path.sep):
         dst += os.path.sep
     return dst.startswith(src)

 def _get_gid(name):
     """Returns a gid, given a group name."""
     if getgrnam is None or name is None:
         return None
     try:
         result = getgrnam(name)
     except KeyError:
         result = None
     if result is not None:
         return result[2]
     return None

 def _get_uid(name):
     """Returns an uid, given a user name."""
     if getpwnam is None or name is None:
         return None
     try:
         result = getpwnam(name)
     except KeyError:
         result = None
     if result is not None:
         return result[2]
     return None

 def _make_tarball(base_name, base_dir, compress="gzip", verbose=0, dry_run=0,
                   owner=None, group=None, logger=None):
     """Create a (possibly compressed) tar file from all the files under
     'base_dir'.

     'compress' must be "gzip" (the default), "bzip2", "xz", or None.

     'owner' and 'group' can be used to define an owner and a group for the
     archive that is being built. If not provided, the current owner and group
     will be used.

     The output tar file will be named 'base_name' +  ".tar", possibly plus
     the appropriate compression extension (".gz", ".bz2", or ".xz").

     Returns the output filename.
     """
     if compress is None:
         tar_compression = ''
     elif _ZLIB_SUPPORTED and compress == 'gzip':
         tar_compression = 'gz'
     elif _BZ2_SUPPORTED and compress == 'bzip2':
         tar_compression = 'bz2'
     elif _LZMA_SUPPORTED and compress == 'xz':
         tar_compression = 'xz'
     else:
         raise ValueError("bad value for 'compress', or compression format not "
                          "supported : {0}".format(compress))

     import tarfile  # late import for breaking circular dependency

     compress_ext = '.' + tar_compression if compress else ''
     archive_name = base_name + '.tar' + compress_ext
     archive_dir = os.path.dirname(archive_name)

     if archive_dir and not os.path.exists(archive_dir):
         if logger is not None:
             logger.info("creating %s", archive_dir)
         if not dry_run:
             os.makedirs(archive_dir)

     # creating the tarball
     if logger is not None:
         logger.info('Creating tar archive')

     uid = _get_uid(owner)
     gid = _get_gid(group)

     def _set_uid_gid(tarinfo):
         if gid is not None:
             tarinfo.gid = gid
             tarinfo.gname = group
         if uid is not None:
             tarinfo.uid = uid
             tarinfo.uname = owner
         return tarinfo

     if not dry_run:
         tar = tarfile.open(archive_name, 'w|%s' % tar_compression)
         try:
             tar.add(base_dir, filter=_set_uid_gid)
         finally:
             tar.close()

     return archive_name

 def _make_zipfile(base_name, base_dir, verbose=0, dry_run=0, logger=None):
     """Create a zip file from all the files under 'base_dir'.

     The output zip file will be named 'base_name' + ".zip".  Returns the
     name of the output zip file.
     """
     import zipfile  # late import for breaking circular dependency

     zip_filename = base_name + ".zip"
     archive_dir = os.path.dirname(base_name)

     if archive_dir and not os.path.exists(archive_dir):
         if logger is not None:
             logger.info("creating %s", archive_dir)
         if not dry_run:
             os.makedirs(archive_dir)

     if logger is not None:
         logger.info("creating '%s' and adding '%s' to it",
                     zip_filename, base_dir)

     if not dry_run:
         with zipfile.ZipFile(zip_filename, "w",
                              compression=zipfile.ZIP_DEFLATED) as zf:
             path = os.path.normpath(base_dir)
             if path != os.curdir:
                 zf.write(path, path)
                 if logger is not None:
                     logger.info("adding '%s'", path)
             for dirpath, dirnames, filenames in os.walk(base_dir):
                 for name in sorted(dirnames):
                     path = os.path.normpath(os.path.join(dirpath, name))
                     zf.write(path, path)
                     if logger is not None:
                         logger.info("adding '%s'", path)
                 for name in filenames:
                     path = os.path.normpath(os.path.join(dirpath, name))
                     if os.path.isfile(path):
                         zf.write(path, path)
                         if logger is not None:
                             logger.info("adding '%s'", path)

     return zip_filename

 _ARCHIVE_FORMATS = {
     'tar':   (_make_tarball, [('compress', None)], "uncompressed tar file"),
 }

 if _ZLIB_SUPPORTED:
     _ARCHIVE_FORMATS['gztar'] = (_make_tarball, [('compress', 'gzip')],
                                 "gzip'ed tar-file")
     _ARCHIVE_FORMATS['zip'] = (_make_zipfile, [], "ZIP file")

 if _BZ2_SUPPORTED:
     _ARCHIVE_FORMATS['bztar'] = (_make_tarball, [('compress', 'bzip2')],
                                 "bzip2'ed tar-file")

 if _LZMA_SUPPORTED:
     _ARCHIVE_FORMATS['xztar'] = (_make_tarball, [('compress', 'xz')],
                                 "xz'ed tar-file")

 def get_archive_formats():
     """Returns a list of supported formats for archiving and unarchiving.

     Each element of the returned sequence is a tuple (name, description)
     """
     formats = [(name, registry[2]) for name, registry in
                _ARCHIVE_FORMATS.items()]
     formats.sort()
     return formats

 def register_archive_format(name, function, extra_args=None, description=''):
     """Registers an archive format.

     name is the name of the format. function is the callable that will be
     used to create archives. If provided, extra_args is a sequence of
     (name, value) tuples that will be passed as arguments to the callable.
     description can be provided to describe the format, and will be returned
     by the get_archive_formats() function.
     """
     if extra_args is None:
         extra_args = []
     if not callable(function):
         raise TypeError('The %s object is not callable' % function)
     if not isinstance(extra_args, (tuple, list)):
         raise TypeError('extra_args needs to be a sequence')
     for element in extra_args:
         if not isinstance(element, (tuple, list)) or len(element) !=2:
             raise TypeError('extra_args elements are : (arg_name, value)')

     _ARCHIVE_FORMATS[name] = (function, extra_args, description)

 def unregister_archive_format(name):
     del _ARCHIVE_FORMATS[name]

 def make_archive(base_name, format, root_dir=None, base_dir=None, verbose=0,
                  dry_run=0, owner=None, group=None, logger=None):
     """Create an archive file (eg. zip or tar).

     'base_name' is the name of the file to create, minus any format-specific
     extension; 'format' is the archive format: one of "zip", "tar", "gztar",
     "bztar", or "xztar".  Or any other registered format.

     'root_dir' is a directory that will be the root directory of the
     archive; ie. we typically chdir into 'root_dir' before creating the
     archive.  'base_dir' is the directory where we start archiving from;
     ie. 'base_dir' will be the common prefix of all files and
     directories in the archive.  'root_dir' and 'base_dir' both default
     to the current directory.  Returns the name of the archive file.

     'owner' and 'group' are used when creating a tar archive. By default,
     uses the current owner and group.
     """
     save_cwd = os.getcwd()
     if root_dir is not None:
         if logger is not None:
             logger.debug("changing into '%s'", root_dir)
         base_name = os.path.abspath(base_name)
         if not dry_run:
             os.chdir(root_dir)

     if base_dir is None:
         base_dir = os.curdir

     kwargs = {'dry_run': dry_run, 'logger': logger}

     try:
         format_info = _ARCHIVE_FORMATS[format]
     except KeyError:
         raise ValueError("unknown archive format '%s'" % format)

     func = format_info[0]
     for arg, val in format_info[1]:
         kwargs[arg] = val

     if format != 'zip':
         kwargs['owner'] = owner
         kwargs['group'] = group

     try:
         filename = func(base_name, base_dir, **kwargs)
     finally:
         if root_dir is not None:
             if logger is not None:
                 logger.debug("changing back to '%s'", save_cwd)
             os.chdir(save_cwd)

     return filename

 def get_unpack_formats():
     """Returns a list of supported formats for unpacking.

     Each element of the returned sequence is a tuple
     (name, extensions, description)
     """
     formats = [(name, info[0], info[3]) for name, info in
                _UNPACK_FORMATS.items()]
     formats.sort()
     return formats

 def _check_unpack_options(extensions, function, extra_args):
     """Checks what gets registered as an unpacker."""
     # first make sure no other unpacker is registered for this extension
     existing_extensions = {}
     for name, info in _UNPACK_FORMATS.items():
         for ext in info[0]:
             existing_extensions[ext] = name

     for extension in extensions:
         if extension in existing_extensions:
             msg = '%s is already registered for "%s"'
             raise RegistryError(msg % (extension,
                                        existing_extensions[extension]))

     if not callable(function):
         raise TypeError('The registered function must be a callable')

 def register_unpack_format(name, extensions, function, extra_args=None,
                            description=''):
     """Registers an unpack format.

     `name` is the name of the format. `extensions` is a list of extensions
     corresponding to the format.

     `function` is the callable that will be
     used to unpack archives. The callable will receive archives to unpack.
     If it's unable to handle an archive, it needs to raise a ReadError
     exception.

     If provided, `extra_args` is a sequence of
     (name, value) tuples that will be passed as arguments to the callable.
     description can be provided to describe the format, and will be returned
     by the get_unpack_formats() function.
     """
     if extra_args is None:
         extra_args = []
     _check_unpack_options(extensions, function, extra_args)
     _UNPACK_FORMATS[name] = extensions, function, extra_args, description

 def unregister_unpack_format(name):
     """Removes the pack format from the registry."""
     del _UNPACK_FORMATS[name]

 def _ensure_directory(path):
     """Ensure that the parent directory of `path` exists"""
     dirname = os.path.dirname(path)
     if not os.path.isdir(dirname):
         os.makedirs(dirname)

 def _unpack_zipfile(filename, extract_dir):
     """Unpack zip `filename` to `extract_dir`
     """
     import zipfile  # late import for breaking circular dependency

     if not zipfile.is_zipfile(filename):
         raise ReadError("%s is not a zip file" % filename)

     zip = zipfile.ZipFile(filename)
     try:
         for info in zip.infolist():
             name = info.filename

             # don't extract absolute paths or ones with .. in them
             if name.startswith('/') or '..' in name:
                 continue

             target = os.path.join(extract_dir, *name.split('/'))
             if not target:
                 continue

             _ensure_directory(target)
             if not name.endswith('/'):
                 # file
                 data = zip.read(info.filename)
                 f = open(target, 'wb')
                 try:
                     f.write(data)
                 finally:
                     f.close()
                     del data
     finally:
         zip.close()

 def _unpack_tarfile(filename, extract_dir):
     """Unpack tar/tar.gz/tar.bz2/tar.xz `filename` to `extract_dir`
     """
     import tarfile  # late import for breaking circular dependency
     try:
         tarobj = tarfile.open(filename)
     except tarfile.TarError:
         raise ReadError(
             "%s is not a compressed or uncompressed tar file" % filename)
     try:
         tarobj.extractall(extract_dir)
     finally:
         tarobj.close()

 _UNPACK_FORMATS = {
     'tar':   (['.tar'], _unpack_tarfile, [], "uncompressed tar file"),
     'zip':   (['.zip'], _unpack_zipfile, [], "ZIP file"),
 }

 if _ZLIB_SUPPORTED:
     _UNPACK_FORMATS['gztar'] = (['.tar.gz', '.tgz'], _unpack_tarfile, [],
                                 "gzip'ed tar-file")

 if _BZ2_SUPPORTED:
     _UNPACK_FORMATS['bztar'] = (['.tar.bz2', '.tbz2'], _unpack_tarfile, [],
                                 "bzip2'ed tar-file")

 if _LZMA_SUPPORTED:
     _UNPACK_FORMATS['xztar'] = (['.tar.xz', '.txz'], _unpack_tarfile, [],
                                 "xz'ed tar-file")

 def _find_unpack_format(filename):
     for name, info in _UNPACK_FORMATS.items():
         for extension in info[0]:
             if filename.endswith(extension):
                 return name
     return None

 def unpack_archive(filename, extract_dir=None, format=None):
     """Unpack an archive.

     `filename` is the name of the archive.

     `extract_dir` is the name of the target directory, where the archive
     is unpacked. If not provided, the current working directory is used.

     `format` is the archive format: one of "zip", "tar", "gztar", "bztar",
     or "xztar".  Or any other registered format.  If not provided,
     unpack_archive will use the filename extension and see if an unpacker
     was registered for that extension.

     In case none is found, a ValueError is raised.
     """
     if extract_dir is None:
         extract_dir = os.getcwd()

     if format is not None:
         try:
             format_info = _UNPACK_FORMATS[format]
         except KeyError:
             raise ValueError("Unknown unpack format '{0}'".format(format))

         func = format_info[1]
         func(filename, extract_dir, **dict(format_info[2]))
     else:
         # we need to look at the registered unpackers supported extensions
         format = _find_unpack_format(filename)
         if format is None:
             raise ReadError("Unknown archive format '{0}'".format(filename))

         func = _UNPACK_FORMATS[format][1]
         kwargs = dict(_UNPACK_FORMATS[format][2])
         func(filename, extract_dir, **kwargs)

 if hasattr(os, 'statvfs'):

     __all__.append('disk_usage')
     _ntuple_diskusage = collections.namedtuple('usage', 'total used free')
     _ntuple_diskusage.total.__doc__ = 'Total space in bytes'
     _ntuple_diskusage.used.__doc__ = 'Used space in bytes'
     _ntuple_diskusage.free.__doc__ = 'Free space in bytes'

     def disk_usage(path):
         """Return disk usage statistics about the given path.

         Returned value is a named tuple with attributes 'total', 'used' and
         'free', which are the amount of total, used and free space, in bytes.
         """
         st = os.statvfs(path)
         free = st.f_bavail * st.f_frsize
         total = st.f_blocks * st.f_frsize
         used = (st.f_blocks - st.f_bfree) * st.f_frsize
         return _ntuple_diskusage(total, used, free)

 elif os.name == 'nt':

     import nt
     __all__.append('disk_usage')
     _ntuple_diskusage = collections.namedtuple('usage', 'total used free')

     def disk_usage(path):
         """Return disk usage statistics about the given path.

         Returned values is a named tuple with attributes 'total', 'used' and
         'free', which are the amount of total, used and free space, in bytes.
         """
         total, free = nt._getdiskusage(path)
         used = total - free
         return _ntuple_diskusage(total, used, free)

 def chown(path, user=None, group=None):
     """Change owner user and group of the given path.

     user and group can be the uid/gid or the user/group names, and in that case,
     they are converted to their respective uid/gid.
     """

     if user is None and group is None:
         raise ValueError("user and/or group must be set")

     _user = user
     _group = group

     # -1 means don't change it
     if user is None:
         _user = -1
     # user can either be an int (the uid) or a string (the system username)
     elif isinstance(user, str):
         _user = _get_uid(user)
         if _user is None:
             raise LookupError("no such user: {!r}".format(user))

     if group is None:
         _group = -1
     elif not isinstance(group, int):
         _group = _get_gid(group)
         if _group is None:
             raise LookupError("no such group: {!r}".format(group))

     os.chown(path, _user, _group)

 def get_terminal_size(fallback=(80, 24)):
     """Get the size of the terminal window.

     For each of the two dimensions, the environment variable, COLUMNS
     and LINES respectively, is checked. If the variable is defined and
     the value is a positive integer, it is used.

     When COLUMNS or LINES is not defined, which is the common case,
     the terminal connected to sys.__stdout__ is queried
     by invoking os.get_terminal_size.

     If the terminal size cannot be successfully queried, either because
     the system doesn't support querying, or because we are not
     connected to a terminal, the value given in fallback parameter
     is used. Fallback defaults to (80, 24) which is the default
     size used by many terminal emulators.

     The value returned is a named tuple of type os.terminal_size.
     """
     # columns, lines are the working values
     try:
         columns = int(os.environ['COLUMNS'])
     except (KeyError, ValueError):
         columns = 0

     try:
         lines = int(os.environ['LINES'])
     except (KeyError, ValueError):
         lines = 0

     # only query if necessary
     if columns <= 0 or lines <= 0:
         try:
             size = os.get_terminal_size(sys.__stdout__.fileno())
         except (AttributeError, ValueError, OSError):
             # stdout is None, closed, detached, or not a terminal, or
             # os.get_terminal_size() is unsupported
             size = os.terminal_size(fallback)
         if columns <= 0:
             columns = size.columns
         if lines <= 0:
             lines = size.lines

     return os.terminal_size((columns, lines))

 def which(cmd, mode=os.F_OK | os.X_OK, path=None):
     """Given a command, mode, and a PATH string, return the path which
     conforms to the given mode on the PATH, or None if there is no such
     file.

     `mode` defaults to os.F_OK | os.X_OK. `path` defaults to the result
     of os.environ.get("PATH"), or can be overridden with a custom search
     path.

     """
     # Check that a given file can be accessed with the correct mode.
     # Additionally check that `file` is not a directory, as on Windows
     # directories pass the os.access check.
     def _access_check(fn, mode):
         return (os.path.exists(fn) and os.access(fn, mode)
                 and not os.path.isdir(fn))

     # If we're given a path with a directory part, look it up directly rather
     # than referring to PATH directories. This includes checking relative to the
     # current directory, e.g. ./script
     if os.path.dirname(cmd):
         if _access_check(cmd, mode):
             return cmd
         return None

     if path is None:
         path = os.environ.get("PATH", os.defpath)
     if not path:
         return None
     path = path.split(os.pathsep)

     if sys.platform == "win32":
         # The current directory takes precedence on Windows.
         if not os.curdir in path:
             path.insert(0, os.curdir)

         # PATHEXT is necessary to check on Windows.
         pathext = os.environ.get("PATHEXT", "").split(os.pathsep)
         # See if the given file matches any of the expected path extensions.
         # This will allow us to short circuit when given "python.exe".
         # If it does match, only test that one, otherwise we have to try
         # others.
         if any(cmd.lower().endswith(ext.lower()) for ext in pathext):
             files = [cmd]
         else:
             files = [cmd + ext for ext in pathext]
     else:
         # On other platforms you don't have things like PATHEXT to tell you
         # what file suffixes are executable, so just pass on cmd as-is.
         files = [cmd]

     seen = set()
     for dir in path:
         normdir = os.path.normcase(dir)
         if not normdir in seen:
             seen.add(normdir)
             for thefile in files:
                 name = os.path.join(dir, thefile)
                 if _access_check(name, mode):
                     return name
     return None

python:shutil