Doc/lib/libtarfile.tex

\section{\module{tarfile} --- Read and write tar archive files}

\declaremodule{standard}{tarfile}
\modulesynopsis{Read and write tar-format archive files.}
\versionadded{2.3}

\moduleauthor{Lars Gust\"abel}{lars@gustaebel.de}
\sectionauthor{Lars Gust\"abel}{lars@gustaebel.de}

The \module{tarfile} module makes it possible to read and create tar archives.
Some facts and figures:

\begin{itemize}
\item reads and writes \module{gzip} and \module{bzip2} compressed archives.
\item read/write support for the \POSIX{}.1-1988 (ustar) format.
\item read/write support for the GNU tar format including \emph{longname} and
      \emph{longlink} extensions, read-only support for the \emph{sparse}
      extension.
\item read/write support for the \POSIX{}.1-2001 (pax) format.
      \versionadded{2.6}
\item handles directories, regular files, hardlinks, symbolic links, fifos,
      character devices and block devices and is able to acquire and
      restore file information like timestamp, access permissions and owner.
\item can handle tape devices.
\end{itemize}

\begin{funcdesc}{open}{name\optional{, mode\optional{,
        fileobj\optional{, bufsize}}}, **kwargs}
    Return a \class{TarFile} object for the pathname \var{name}.
    For detailed information on \class{TarFile} objects and the keyword
    arguments that are allowed, see \citetitle{TarFile Objects}
    (section \ref{tarfile-objects}).

    \var{mode} has to be a string of the form \code{'filemode[:compression]'},
    it defaults to \code{'r'}. Here is a full list of mode combinations:

    \begin{tableii}{c|l}{code}{mode}{action}
    \lineii{'r' or 'r:*'}{Open for reading with transparent compression (recommended).}
    \lineii{'r:'}{Open for reading exclusively without compression.}
    \lineii{'r:gz'}{Open for reading with gzip compression.}
    \lineii{'r:bz2'}{Open for reading with bzip2 compression.}
    \lineii{'a' or 'a:'}{Open for appending with no compression. The file
        is created if it does not exist.}
    \lineii{'w' or 'w:'}{Open for uncompressed writing.}
    \lineii{'w:gz'}{Open for gzip compressed writing.}
    \lineii{'w:bz2'}{Open for bzip2 compressed writing.}
    \end{tableii}

    Note that \code{'a:gz'} or \code{'a:bz2'} is not possible.
    If \var{mode} is not suitable to open a certain (compressed) file for
    reading, \exception{ReadError} is raised. Use \var{mode} \code{'r'} to
    avoid this.  If a compression method is not supported,
    \exception{CompressionError} is raised.

    If \var{fileobj} is specified, it is used as an alternative to a file
    object opened for \var{name}. It is supposed to be at position 0.

    For special purposes, there is a second format for \var{mode}:
    \code{'filemode|[compression]'}.  \function{open()} will return a
    \class{TarFile} object that processes its data as a stream of
    blocks.  No random seeking will be done on the file. If given,
    \var{fileobj} may be any object that has a \method{read()} or
    \method{write()} method (depending on the \var{mode}).
    \var{bufsize} specifies the blocksize and defaults to \code{20 *
    512} bytes. Use this variant in combination with
    e.g. \code{sys.stdin}, a socket file object or a tape device.
    However, such a \class{TarFile} object is limited in that it does
    not allow to be accessed randomly, see ``Examples''
    (section~\ref{tar-examples}).  The currently possible modes:

    \begin{tableii}{c|l}{code}{Mode}{Action}
    \lineii{'r|*'}{Open a \emph{stream} of tar blocks for reading with transparent compression.}
    \lineii{'r|'}{Open a \emph{stream} of uncompressed tar blocks for reading.}
    \lineii{'r|gz'}{Open a gzip compressed \emph{stream} for reading.}
    \lineii{'r|bz2'}{Open a bzip2 compressed \emph{stream} for reading.}
    \lineii{'w|'}{Open an uncompressed \emph{stream} for writing.}
    \lineii{'w|gz'}{Open an gzip compressed \emph{stream} for writing.}
    \lineii{'w|bz2'}{Open an bzip2 compressed \emph{stream} for writing.}
    \end{tableii}
\end{funcdesc}

\begin{classdesc*}{TarFile}
    Class for reading and writing tar archives. Do not use this
    class directly, better use \function{open()} instead.
    See ``TarFile Objects'' (section~\ref{tarfile-objects}).
\end{classdesc*}

\begin{funcdesc}{is_tarfile}{name}
    Return \constant{True} if \var{name} is a tar archive file, that
    the \module{tarfile} module can read.
\end{funcdesc}

\begin{classdesc}{TarFileCompat}{filename\optional{, mode\optional{,
                                 compression}}}
    Class for limited access to tar archives with a
    \refmodule{zipfile}-like interface. Please consult the
    documentation of the \refmodule{zipfile} module for more details.
    \var{compression} must be one of the following constants:
    \begin{datadesc}{TAR_PLAIN}
        Constant for an uncompressed tar archive.
    \end{datadesc}
    \begin{datadesc}{TAR_GZIPPED}
        Constant for a \refmodule{gzip} compressed tar archive.
    \end{datadesc}
\end{classdesc}

\begin{excdesc}{TarError}
    Base class for all \module{tarfile} exceptions.
\end{excdesc}

\begin{excdesc}{ReadError}
    Is raised when a tar archive is opened, that either cannot be handled by
    the \module{tarfile} module or is somehow invalid.
\end{excdesc}

\begin{excdesc}{CompressionError}
    Is raised when a compression method is not supported or when the data
    cannot be decoded properly.
\end{excdesc}

\begin{excdesc}{StreamError}
    Is raised for the limitations that are typical for stream-like
    \class{TarFile} objects.
\end{excdesc}

\begin{excdesc}{ExtractError}
    Is raised for \emph{non-fatal} errors when using \method{extract()}, but
    only if \member{TarFile.errorlevel}\code{ == 2}.
\end{excdesc}

\begin{excdesc}{HeaderError}
    Is raised by \method{frombuf()} if the buffer it gets is invalid.
    \versionadded{2.6}
\end{excdesc}

Each of the following constants defines a tar archive format that the
\module{tarfile} module is able to create. See section \ref{tar-formats} for
details.

\begin{datadesc}{USTAR_FORMAT}
    \POSIX{}.1-1988 (ustar) format.
\end{datadesc}

\begin{datadesc}{GNU_FORMAT}
    GNU tar format.
\end{datadesc}

\begin{datadesc}{PAX_FORMAT}
    \POSIX{}.1-2001 (pax) format.
\end{datadesc}

\begin{datadesc}{DEFAULT_FORMAT}
    The default format for creating archives. This is currently
    \constant{GNU_FORMAT}.
\end{datadesc}

\begin{seealso}
    \seemodule{zipfile}{Documentation of the \refmodule{zipfile}
    standard module.}

    \seetitle[http://www.gnu.org/software/tar/manual/html_node/tar_134.html\#SEC134]
    {GNU tar manual, Basic Tar Format}{Documentation for tar archive files,
    including GNU tar extensions.}
\end{seealso}

%-----------------
% TarFile Objects
%-----------------

\subsection{TarFile Objects \label{tarfile-objects}}

The \class{TarFile} object provides an interface to a tar archive. A tar
archive is a sequence of blocks. An archive member (a stored file) is made up
of a header block followed by data blocks. It is possible to store a file in a
tar archive several times. Each archive member is represented by a
\class{TarInfo} object, see \citetitle{TarInfo Objects} (section
\ref{tarinfo-objects}) for details.

\begin{classdesc}{TarFile}{name=None, mode='r', fileobj=None,
        format=DEFAULT_FORMAT, tarinfo=TarInfo, dereference=False,
        ignore_zeros=False, encoding=None, errors=None, pax_headers=None,
        debug=0, errorlevel=0}

    All following arguments are optional and can be accessed as instance
    attributes as well.

    \var{name} is the pathname of the archive. It can be omitted if
    \var{fileobj} is given. In this case, the file object's \member{name}
    attribute is used if it exists.

    \var{mode} is either \code{'r'} to read from an existing archive,
    \code{'a'} to append data to an existing file or \code{'w'} to create a new
    file overwriting an existing one.

    If \var{fileobj} is given, it is used for reading or writing data.
    If it can be determined, \var{mode} is overridden by \var{fileobj}'s mode.
    \var{fileobj} will be used from position 0.
    \begin{notice}
        \var{fileobj} is not closed, when \class{TarFile} is closed.
    \end{notice}

    \var{format} controls the archive format. It must be one of the constants
    \constant{USTAR_FORMAT}, \constant{GNU_FORMAT} or \constant{PAX_FORMAT}
    that are defined at module level.
    \versionadded{2.6}

    The \var{tarinfo} argument can be used to replace the default
    \class{TarInfo} class with a different one.
    \versionadded{2.6}

    If \var{dereference} is \code{False}, add symbolic and hard links to the
    archive. If it is \code{True}, add the content of the target files to the
    archive. This has no effect on systems that do not support symbolic links.

    If \var{ignore_zeros} is \code{False}, treat an empty block as the end of
    the archive. If it is \var{True}, skip empty (and invalid) blocks and try
    to get as many members as possible. This is only useful for reading
    concatenated or damaged archives.

    \var{debug} can be set from \code{0} (no debug messages) up to \code{3}
    (all debug messages). The messages are written to \code{sys.stderr}.

    If \var{errorlevel} is \code{0}, all errors are ignored when using
    \method{extract()}.  Nevertheless, they appear as error messages in the
    debug output, when debugging is enabled.  If \code{1}, all \emph{fatal}
    errors are raised as \exception{OSError} or \exception{IOError} exceptions.
    If \code{2}, all \emph{non-fatal} errors are raised as \exception{TarError}
    exceptions as well.

    The \var{encoding} and \var{errors} arguments control the way strings are
    converted to unicode objects and vice versa. The default settings will work
    for most users. See section \ref{tar-unicode} for in-depth information.
    \versionadded{2.6}

    The \var{pax_headers} argument is an optional dictionary of unicode strings
    which will be added as a pax global header if \var{format} is
    \constant{PAX_FORMAT}.
    \versionadded{2.6}
\end{classdesc}

\begin{methoddesc}{open}{...}
    Alternative constructor. The \function{open()} function on module level is
    actually a shortcut to this classmethod. See section~\ref{module-tarfile}
    for details.
\end{methoddesc}

\begin{methoddesc}{getmember}{name}
    Return a \class{TarInfo} object for member \var{name}. If \var{name} can
    not be found in the archive, \exception{KeyError} is raised.
    \begin{notice}
        If a member occurs more than once in the archive, its last
        occurrence is assumed to be the most up-to-date version.
    \end{notice}
\end{methoddesc}

\begin{methoddesc}{getmembers}{}
    Return the members of the archive as a list of \class{TarInfo} objects.
    The list has the same order as the members in the archive.
\end{methoddesc}

\begin{methoddesc}{getnames}{}
    Return the members as a list of their names. It has the same order as
    the list returned by \method{getmembers()}.
\end{methoddesc}

\begin{methoddesc}{list}{verbose=True}
    Print a table of contents to \code{sys.stdout}. If \var{verbose} is
    \constant{False}, only the names of the members are printed. If it is
    \constant{True}, output similar to that of \program{ls -l} is produced.
\end{methoddesc}

\begin{methoddesc}{next}{}
    Return the next member of the archive as a \class{TarInfo} object, when
    \class{TarFile} is opened for reading. Return \code{None} if there is no
    more available.
\end{methoddesc}

\begin{methoddesc}{extractall}{\optional{path\optional{, members}}}
    Extract all members from the archive to the current working directory
    or directory \var{path}. If optional \var{members} is given, it must be
    a subset of the list returned by \method{getmembers()}.
    Directory information like owner, modification time and permissions are
    set after all members have been extracted. This is done to work around two
    problems: A directory's modification time is reset each time a file is
    created in it. And, if a directory's permissions do not allow writing,
    extracting files to it will fail.
    \versionadded{2.5}
\end{methoddesc}

\begin{methoddesc}{extract}{member\optional{, path}}
    Extract a member from the archive to the current working directory,
    using its full name. Its file information is extracted as accurately as
    possible.
    \var{member} may be a filename or a \class{TarInfo} object.
    You can specify a different directory using \var{path}.
    \begin{notice}
    Because the \method{extract()} method allows random access to a tar
    archive there are some issues you must take care of yourself. See the
    description for \method{extractall()} above.
    \end{notice}
\end{methoddesc}

\begin{methoddesc}{extractfile}{member}
    Extract a member from the archive as a file object.
    \var{member} may be a filename or a \class{TarInfo} object.
    If \var{member} is a regular file, a file-like object is returned.
    If \var{member} is a link, a file-like object is constructed from the
    link's target.
    If \var{member} is none of the above, \code{None} is returned.
    \begin{notice}
        The file-like object is read-only and provides the following methods:
        \method{read()}, \method{readline()}, \method{readlines()},
        \method{seek()}, \method{tell()}.
    \end{notice}
\end{methoddesc}

\begin{methoddesc}{add}{name\optional{, arcname\optional{, recursive\optional{, exclude}}}}
    Add the file \var{name} to the archive. \var{name} may be any type
    of file (directory, fifo, symbolic link, etc.).
    If given, \var{arcname} specifies an alternative name for the file in the
    archive. Directories are added recursively by default.
    This can be avoided by setting \var{recursive} to \constant{False}.
    If \var{exclude} is given it must be a function that takes one filename
    argument and returns a boolean value. Depending on this value the
    respective file is either excluded (\constant{True}) or added
    (\constant{False}).
\end{methoddesc}

\begin{methoddesc}{addfile}{tarinfo\optional{, fileobj}}
    Add the \class{TarInfo} object \var{tarinfo} to the archive.
    If \var{fileobj} is given, \code{\var{tarinfo}.size} bytes are read
    from it and added to the archive.  You can create \class{TarInfo} objects
    using \method{gettarinfo()}.
    \begin{notice}
    On Windows platforms, \var{fileobj} should always be opened with mode
    \code{'rb'} to avoid irritation about the file size.
    \end{notice}
\end{methoddesc}

\begin{methoddesc}{gettarinfo}{\optional{name\optional{,
                               arcname\optional{, fileobj}}}}
    Create a \class{TarInfo} object for either the file \var{name} or
    the file object \var{fileobj} (using \function{os.fstat()} on its
    file descriptor).  You can modify some of the \class{TarInfo}'s
    attributes before you add it using \method{addfile()}.  If given,
    \var{arcname} specifies an alternative name for the file in the
    archive.
\end{methoddesc}

\begin{methoddesc}{close}{}
    Close the \class{TarFile}. In write mode, two finishing zero
    blocks are appended to the archive.
\end{methoddesc}

\begin{memberdesc}{posix}
    Setting this to \constant{True} is equivalent to setting the
    \member{format} attribute to \constant{USTAR_FORMAT},
    \constant{False} is equivalent to \constant{GNU_FORMAT}.
    \versionchanged[\var{posix} defaults to \constant{False}]{2.4}
    \deprecated{2.6}{Use the \member{format} attribute instead.}
\end{memberdesc}

\begin{memberdesc}{pax_headers}
    A dictionary containing key-value pairs of pax global headers.
    \versionadded{2.6}
\end{memberdesc}

%-----------------
% TarInfo Objects
%-----------------

\subsection{TarInfo Objects \label{tarinfo-objects}}

A \class{TarInfo} object represents one member in a
\class{TarFile}. Aside from storing all required attributes of a file
(like file type, size, time, permissions, owner etc.), it provides
some useful methods to determine its type. It does \emph{not} contain
the file's data itself.

\class{TarInfo} objects are returned by \class{TarFile}'s methods
\method{getmember()}, \method{getmembers()} and \method{gettarinfo()}.

\begin{classdesc}{TarInfo}{\optional{name}}
    Create a \class{TarInfo} object.
\end{classdesc}

\begin{methoddesc}{frombuf}{buf}
    Create and return a \class{TarInfo} object from string buffer \var{buf}.
    \versionadded[Raises \exception{HeaderError} if the buffer is
    invalid.]{2.6}
\end{methoddesc}

\begin{methoddesc}{fromtarfile}{tarfile}
    Read the next member from the \class{TarFile} object \var{tarfile} and
    return it as a \class{TarInfo} object.
    \versionadded{2.6}
\end{methoddesc}

\begin{methoddesc}{tobuf}{\optional{format\optional{, encoding
        \optional{, errors}}}}
    Create a string buffer from a \class{TarInfo} object. For information
    on the arguments see the constructor of the \class{TarFile} class.
    \versionchanged[The arguments were added]{2.6}
\end{methoddesc}

A \code{TarInfo} object has the following public data attributes:

\begin{memberdesc}{name}
    Name of the archive member.
\end{memberdesc}

\begin{memberdesc}{size}
    Size in bytes.
\end{memberdesc}

\begin{memberdesc}{mtime}
    Time of last modification.
\end{memberdesc}

\begin{memberdesc}{mode}
    Permission bits.
\end{memberdesc}

\begin{memberdesc}{type}
    File type.  \var{type} is usually one of these constants:
    \constant{REGTYPE}, \constant{AREGTYPE}, \constant{LNKTYPE},
    \constant{SYMTYPE}, \constant{DIRTYPE}, \constant{FIFOTYPE},
    \constant{CONTTYPE}, \constant{CHRTYPE}, \constant{BLKTYPE},
    \constant{GNUTYPE_SPARSE}.  To determine the type of a
    \class{TarInfo} object more conveniently, use the \code{is_*()}
    methods below.
\end{memberdesc}

\begin{memberdesc}{linkname}
    Name of the target file name, which is only present in
    \class{TarInfo} objects of type \constant{LNKTYPE} and
    \constant{SYMTYPE}.
\end{memberdesc}

\begin{memberdesc}{uid}
    User ID of the user who originally stored this member.
\end{memberdesc}

\begin{memberdesc}{gid}
    Group ID of the user who originally stored this member.
\end{memberdesc}

\begin{memberdesc}{uname}
    User name.
\end{memberdesc}

\begin{memberdesc}{gname}
    Group name.
\end{memberdesc}

\begin{memberdesc}{pax_headers}
    A dictionary containing key-value pairs of an associated pax
    extended header.
    \versionadded{2.6}
\end{memberdesc}

A \class{TarInfo} object also provides some convenient query methods:

\begin{methoddesc}{isfile}{}
    Return \constant{True} if the \class{Tarinfo} object is a regular
    file.
\end{methoddesc}

\begin{methoddesc}{isreg}{}
    Same as \method{isfile()}.
\end{methoddesc}

\begin{methoddesc}{isdir}{}
    Return \constant{True} if it is a directory.
\end{methoddesc}

\begin{methoddesc}{issym}{}
    Return \constant{True} if it is a symbolic link.
\end{methoddesc}

\begin{methoddesc}{islnk}{}
    Return \constant{True} if it is a hard link.
\end{methoddesc}

\begin{methoddesc}{ischr}{}
    Return \constant{True} if it is a character device.
\end{methoddesc}

\begin{methoddesc}{isblk}{}
    Return \constant{True} if it is a block device.
\end{methoddesc}

\begin{methoddesc}{isfifo}{}
    Return \constant{True} if it is a FIFO.
\end{methoddesc}

\begin{methoddesc}{isdev}{}
    Return \constant{True} if it is one of character device, block
    device or FIFO.
\end{methoddesc}

%------------------------
% Examples
%------------------------

\subsection{Examples \label{tar-examples}}

How to extract an entire tar archive to the current working directory:
\begin{verbatim}
import tarfile
tar = tarfile.open("sample.tar.gz")
tar.extractall()
tar.close()
\end{verbatim}

How to create an uncompressed tar archive from a list of filenames:
\begin{verbatim}
import tarfile
tar = tarfile.open("sample.tar", "w")
for name in ["foo", "bar", "quux"]:
    tar.add(name)
tar.close()
\end{verbatim}

How to read a gzip compressed tar archive and display some member information:
\begin{verbatim}
import tarfile
tar = tarfile.open("sample.tar.gz", "r:gz")
for tarinfo in tar:
    print tarinfo.name, "is", tarinfo.size, "bytes in size and is",
    if tarinfo.isreg():
        print "a regular file."
    elif tarinfo.isdir():
        print "a directory."
    else:
        print "something else."
tar.close()
\end{verbatim}

How to create a tar archive with faked information:
\begin{verbatim}
import tarfile
tar = tarfile.open("sample.tar.gz", "w:gz")
for name in namelist:
    tarinfo = tar.gettarinfo(name, "fakeproj-1.0/" + name)
    tarinfo.uid = 123
    tarinfo.gid = 456
    tarinfo.uname = "johndoe"
    tarinfo.gname = "fake"
    tar.addfile(tarinfo, file(name))
tar.close()
\end{verbatim}

The \emph{only} way to extract an uncompressed tar stream from
\code{sys.stdin}:
\begin{verbatim}
import sys
import tarfile
tar = tarfile.open(mode="r|", fileobj=sys.stdin)
for tarinfo in tar:
    tar.extract(tarinfo)
tar.close()
\end{verbatim}

%------------
% Tar format
%------------

\subsection{Supported tar formats \label{tar-formats}}

There are three tar formats that can be created with the \module{tarfile}
module:

\begin{itemize}

\item
The \POSIX{}.1-1988 ustar format (\constant{USTAR_FORMAT}). It supports
filenames up to a length of at best 256 characters and linknames up to 100
characters. The maximum file size is 8 gigabytes. This is an old and limited
but widely supported format.

\item
The GNU tar format (\constant{GNU_FORMAT}). It supports long filenames and
linknames, files bigger than 8 gigabytes and sparse files. It is the de facto
standard on GNU/Linux systems. \module{tarfile} fully supports the GNU tar
extensions for long names, sparse file support is read-only.

\item
The \POSIX{}.1-2001 pax format (\constant{PAX_FORMAT}). It is the most
flexible format with virtually no limits. It supports long filenames and
linknames, large files and stores pathnames in a portable way. However, not
all tar implementations today are able to handle pax archives properly.

The \emph{pax} format is an extension to the existing \emph{ustar} format. It
uses extra headers for information that cannot be stored otherwise. There are
two flavours of pax headers: Extended headers only affect the subsequent file
header, global headers are valid for the complete archive and affect all
following files. All the data in a pax header is encoded in \emph{UTF-8} for
portability reasons.

\end{itemize}

There are some more variants of the tar format which can be read, but not
created:

\begin{itemize}

\item
The ancient V7 format. This is the first tar format from \UNIX{} Seventh
Edition, storing only regular files and directories. Names must not be longer
than 100 characters, there is no user/group name information. Some archives
have miscalculated header checksums in case of fields with non-\ASCII{}
characters.

\item
The SunOS tar extended format. This format is a variant of the \POSIX{}.1-2001
pax format, but is not compatible.

\end{itemize}

%----------------
% Unicode issues
%----------------

\subsection{Unicode issues \label{tar-unicode}}

The tar format was originally conceived to make backups on tape drives with the
main focus on preserving file system information. Nowadays tar archives are
commonly used for file distribution and exchanging archives over networks. One
problem of the original format (that all other formats are merely variants of)
is that there is no concept of supporting different character encodings.
For example, an ordinary tar archive created on a \emph{UTF-8} system cannot be
read correctly on a \emph{Latin-1} system if it contains non-\ASCII{}
characters. Names (i.e. filenames, linknames, user/group names) containing
these characters will appear damaged.  Unfortunately, there is no way to
autodetect the encoding of an archive.

The pax format was designed to solve this problem. It stores non-\ASCII{} names
using the universal character encoding \emph{UTF-8}. When a pax archive is
read, these \emph{UTF-8} names are converted to the encoding of the local
file system.

The details of unicode conversion are controlled by the \var{encoding} and
\var{errors} keyword arguments of the \class{TarFile} class.

The default value for \var{encoding} is the local character encoding. It is
deduced from \function{sys.getfilesystemencoding()} and
\function{sys.getdefaultencoding()}. In read mode, \var{encoding} is used
exclusively to convert unicode names from a pax archive to strings in the local
character encoding. In write mode, the use of \var{encoding} depends on the
chosen archive format. In case of \constant{PAX_FORMAT}, input names that
contain non-\ASCII{} characters need to be decoded before being stored as
\emph{UTF-8} strings. The other formats do not make use of \var{encoding}
unless unicode objects are used as input names. These are converted to
8-bit character strings before they are added to the archive.

The \var{errors} argument defines how characters are treated that cannot be
converted to or from \var{encoding}. Possible values are listed in section
\ref{codec-base-classes}. In read mode, there is an additional scheme
\code{'utf-8'} which means that bad characters are replaced by their
\emph{UTF-8} representation. This is the default scheme. In write mode the
default value for \var{errors} is \code{'strict'} to ensure that name
information is not altered unnoticed.