
``lzma`` --- Compression using the LZMA algorithm
*************************************************

New in version 3.3.

This module provides classes and convenience functions for compressing
and decompressing data using the LZMA compression algorithm. Also
included is a file interface supporting the ``.xz`` and legacy
``.lzma`` file formats used by the **xz** utility, as well as raw
compressed streams.

The interface provided by this module is very similar to that of the
``bz2`` module. However, note that ``LZMAFile`` is *not* thread-safe,
unlike ``bz2.BZ2File``, so if you need to use a single ``LZMAFile``
instance from multiple threads, it is necessary to protect it with a
lock.

exception exception lzma.LZMAError

   This exception is raised when an error occurs during compression or
   decompression, or while initializing the compressor/decompressor
   state.


Reading and writing compressed files
====================================

lzma.open(filename, mode="rb", *, format=None, check=-1, preset=None, filters=None, encoding=None, errors=None, newline=None)

   Open an LZMA-compressed file in binary or text mode, returning a
   *file object*.

   The *filename* argument can be either an actual file name (given as
   a ``str`` or ``bytes`` object), in which case the named file is
   opened, or it can be an existing file object to read from or write
   to.

   The *mode* argument can be any of ``"r"``, ``"rb"``, ``"w"``,
   ``"wb"``, ``"a"`` or ``"ab"`` for binary mode, or ``"rt"``,
   ``"wt"``, or ``"at"`` for text mode. The default is ``"rb"``.

   When opening a file for reading, the *format* and *filters*
   arguments have the same meanings as for ``LZMADecompressor``. In
   this case, the *check* and *preset* arguments should not be used.

   When opening a file for writing, the *format*, *check*, *preset*
   and *filters* arguments have the same meanings as for
   ``LZMACompressor``.

   For binary mode, this function is equivalent to the ``LZMAFile``
   constructor: ``LZMAFile(filename, mode, ...)``. In this case, the
   *encoding*, *errors* and *newline* arguments must not be provided.

   For text mode, a ``LZMAFile`` object is created, and wrapped in an
   ``io.TextIOWrapper`` instance with the specified encoding, error
   handling behavior, and line ending(s).

class class lzma.LZMAFile(filename=None, mode="r", *, format=None, check=-1, preset=None, filters=None)

   Open an LZMA-compressed file in binary mode.

   An ``LZMAFile`` can wrap an already-open *file object*, or operate
   directly on a named file. The *filename* argument specifies either
   the file object to wrap, or the name of the file to open (as a
   ``str`` or ``bytes`` object). When wrapping an existing file
   object, the wrapped file will not be closed when the ``LZMAFile``
   is closed.

   The *mode* argument can be either ``"r"`` for reading (default),
   ``"w"`` for overwriting, or ``"a"`` for appending. These can
   equivalently be given as ``"rb"``, ``"wb"``, and ``"ab"``
   respectively.

   If *filename* is a file object (rather than an actual file name), a
   mode of ``"w"`` does not truncate the file, and is instead
   equivalent to ``"a"``.

   When opening a file for reading, the input file may be the
   concatenation of multiple separate compressed streams. These are
   transparently decoded as a single logical stream.

   When opening a file for reading, the *format* and *filters*
   arguments have the same meanings as for ``LZMADecompressor``. In
   this case, the *check* and *preset* arguments should not be used.

   When opening a file for writing, the *format*, *check*, *preset*
   and *filters* arguments have the same meanings as for
   ``LZMACompressor``.

   ``LZMAFile`` supports all the members specified by
   ``io.BufferedIOBase``, except for ``detach()`` and ``truncate()``.
   Iteration and the ``with`` statement are supported.

   The following method is also provided:

   peek(size=-1)

      Return buffered data without advancing the file position. At
      least one byte of data will be returned, unless EOF has been
      reached. The exact number of bytes returned is unspecified (the
      *size* argument is ignored).


Compressing and decompressing data in memory
============================================

class class lzma.LZMACompressor(format=FORMAT_XZ, check=-1, preset=None, filters=None)

   Create a compressor object, which can be used to compress data
   incrementally.

   For a more convenient way of compressing a single chunk of data,
   see ``compress()``.

   The *format* argument specifies what container format should be
   used. Possible values are:

   * ``FORMAT_XZ``: The ``.xz`` container format.
        This is the default format.

   * ``FORMAT_ALONE``: The legacy ``.lzma`` container format.
        This format is more limited than ``.xz`` -- it does not
        support integrity checks or multiple filters.

   * ``FORMAT_RAW``: A raw data stream, not using any container
     format.
        This format specifier does not support integrity checks, and
        requires that you always specify a custom filter chain (for
        both compression and decompression). Additionally, data
        compressed in this manner cannot be decompressed using
        ``FORMAT_AUTO`` (see ``LZMADecompressor``).

   The *check* argument specifies the type of integrity check to
   include in the compressed data. This check is used when
   decompressing, to ensure that the data has not been corrupted.
   Possible values are:

   * ``CHECK_NONE``: No integrity check. This is the default (and the
     only acceptable value) for ``FORMAT_ALONE`` and ``FORMAT_RAW``.

   * ``CHECK_CRC32``: 32-bit Cyclic Redundancy Check.

   * ``CHECK_CRC64``: 64-bit Cyclic Redundancy Check. This is the
     default for ``FORMAT_XZ``.

   * ``CHECK_SHA256``: 256-bit Secure Hash Algorithm.

   If the specified check is not supported, an ``LZMAError`` is
   raised.

   The compression settings can be specified either as a preset
   compression level (with the *preset* argument), or in detail as a
   custom filter chain (with the *filters* argument).

   The *preset* argument (if provided) should be an integer between
   ``0`` and ``9`` (inclusive), optionally OR-ed with the constant
   ``PRESET_EXTREME``. If neither *preset* nor *filters* are given,
   the default behavior is to use ``PRESET_DEFAULT`` (preset level
   ``6``). Higher presets produce smaller output, but make the
   compression process slower.

   Note: In addition to being more CPU-intensive, compression with higher
     presets also requires much more memory (and produces output that
     needs more memory to decompress). With preset ``9`` for example,
     the overhead for an ``LZMACompressor`` object can be as high as
     800 MiB. For this reason, it is generally best to stick with the
     default preset.

   The *filters* argument (if provided) should be a filter chain
   specifier. See *Specifying custom filter chains* for details.

   compress(data)

      Compress *data* (a ``bytes`` object), returning a ``bytes``
      object containing compressed data for at least part of the
      input. Some of *data* may be buffered internally, for use in
      later calls to ``compress()`` and ``flush()``. The returned data
      should be concatenated with the output of any previous calls to
      ``compress()``.

   flush()

      Finish the compression process, returning a ``bytes`` object
      containing any data stored in the compressor's internal buffers.

      The compressor cannot be used after this method has been called.

class class lzma.LZMADecompressor(format=FORMAT_AUTO, memlimit=None, filters=None)

   Create a decompressor object, which can be used to decompress data
   incrementally.

   For a more convenient way of decompressing an entire compressed
   stream at once, see ``decompress()``.

   The *format* argument specifies the container format that should be
   used. The default is ``FORMAT_AUTO``, which can decompress both
   ``.xz`` and ``.lzma`` files. Other possible values are
   ``FORMAT_XZ``, ``FORMAT_ALONE``, and ``FORMAT_RAW``.

   The *memlimit* argument specifies a limit (in bytes) on the amount
   of memory that the decompressor can use. When this argument is
   used, decompression will fail with an ``LZMAError`` if it is not
   possible to decompress the input within the given memory limit.

   The *filters* argument specifies the filter chain that was used to
   create the stream being decompressed. This argument is required if
   *format* is ``FORMAT_RAW``, but should not be used for other
   formats. See *Specifying custom filter chains* for more information
   about filter chains.

   Note: This class does not transparently handle inputs containing
     multiple compressed streams, unlike ``decompress()`` and
     ``LZMAFile``. To decompress a multi-stream input with
     ``LZMADecompressor``, you must create a new decompressor for each
     stream.

   decompress(data)

      Decompress *data* (a ``bytes`` object), returning a ``bytes``
      object containing the decompressed data for at least part of the
      input. Some of *data* may be buffered internally, for use in
      later calls to ``decompress()``. The returned data should be
      concatenated with the output of any previous calls to
      ``decompress()``.

   check

      The ID of the integrity check used by the input stream. This may
      be ``CHECK_UNKNOWN`` until enough of the input has been decoded
      to determine what integrity check it uses.

   eof

      True if the end-of-stream marker has been reached.

   unused_data

      Data found after the end of the compressed stream.

      Before the end of the stream is reached, this will be ``b""``.

lzma.compress(data, format=FORMAT_XZ, check=-1, preset=None, filters=None)

   Compress *data* (a ``bytes`` object), returning the compressed data
   as a ``bytes`` object.

   See ``LZMACompressor`` above for a description of the *format*,
   *check*, *preset* and *filters* arguments.

lzma.decompress(data, format=FORMAT_AUTO, memlimit=None, filters=None)

   Decompress *data* (a ``bytes`` object), returning the uncompressed
   data as a ``bytes`` object.

   If *data* is the concatenation of multiple distinct compressed
   streams, decompress all of these streams, and return the
   concatenation of the results.

   See ``LZMADecompressor`` above for a description of the *format*,
   *memlimit* and *filters* arguments.


Miscellaneous
=============

lzma.is_check_supported(check)

   Returns true if the given integrity check is supported on this
   system.

   ``CHECK_NONE`` and ``CHECK_CRC32`` are always supported.
   ``CHECK_CRC64`` and ``CHECK_SHA256`` may be unavailable if you are
   using a version of **liblzma** that was compiled with a limited
   feature set.


Specifying custom filter chains
===============================

A filter chain specifier is a sequence of dictionaries, where each
dictionary contains the ID and options for a single filter. Each
dictionary must contain the key ``"id"``, and may contain additional
keys to specify filter-dependent options. Valid filter IDs are as
follows:

* Compression filters:
     * ``FILTER_LZMA1`` (for use with ``FORMAT_ALONE``)

     * ``FILTER_LZMA2`` (for use with ``FORMAT_XZ`` and
       ``FORMAT_RAW``)

* Delta filter:
     * ``FILTER_DELTA``

* Branch-Call-Jump (BCJ) filters:
     * ``FILTER_X86``

     * ``FILTER_IA64``

     * ``FILTER_ARM``

     * ``FILTER_ARMTHUMB``

     * ``FILTER_POWERPC``

     * ``FILTER_SPARC``

A filter chain can consist of up to 4 filters, and cannot be empty.
The last filter in the chain must be a compression filter, and any
other filters must be delta or BCJ filters.

Compression filters support the following options (specified as
additional entries in the dictionary representing the filter):

   * ``preset``: A compression preset to use as a source of default
     values for options that are not specified explicitly.

   * ``dict_size``: Dictionary size in bytes. This should be between 4
     KiB and 1.5 GiB (inclusive).

   * ``lc``: Number of literal context bits.

   * ``lp``: Number of literal position bits. The sum ``lc + lp`` must
     be at most 4.

   * ``pb``: Number of position bits; must be at most 4.

   * ``mode``: ``MODE_FAST`` or ``MODE_NORMAL``.

   * ``nice_len``: What should be considered a "nice length" for a
     match. This should be 273 or less.

   * ``mf``: What match finder to use -- ``MF_HC3``, ``MF_HC4``,
     ``MF_BT2``, ``MF_BT3``, or ``MF_BT4``.

   * ``depth``: Maximum search depth used by match finder. 0 (default)
     means to select automatically based on other filter options.

The delta filter stores the differences between bytes, producing more
repetitive input for the compressor in certain circumstances. It only
supports a single The delta filter supports only one option, ``dist``.
This indicates the distance between bytes to be subtracted. The
default is 1, i.e. take the differences between adjacent bytes.

The BCJ filters are intended to be applied to machine code. They
convert relative branches, calls and jumps in the code to use absolute
addressing, with the aim of increasing the redundancy that can be
exploited by the compressor. These filters support one option,
``start_offset``. This specifies the address that should be mapped to
the beginning of the input data. The default is 0.


Examples
========

Reading in a compressed file:

   import lzma
   with lzma.open("file.xz") as f:
       file_content = f.read()

Creating a compressed file:

   import lzma
   data = b"Insert Data Here"
   with lzma.open("file.xz", "w") as f:
       f.write(data)

Compressing data in memory:

   import lzma
   data_in = b"Insert Data Here"
   data_out = lzma.compress(data_in)

Incremental compression:

   import lzma
   lzc = lzma.LZMACompressor()
   out1 = lzc.compress(b"Some data\n")
   out2 = lzc.compress(b"Another piece of data\n")
   out3 = lzc.compress(b"Even more data\n")
   out4 = lzc.flush()
   # Concatenate all the partial results:
   result = b"".join([out1, out2, out3, out4])

Writing compressed data to an already-open file:

   import lzma
   with open("file.xz", "wb") as f:
       f.write(b"This data will not be compressed\n")
       with lzma.open(f, "w") as lzf:
           lzf.write(b"This *will* be compressed\n")
       f.write(b"Not compressed\n")

Creating a compressed file using a custom filter chain:

   import lzma
   my_filters = [
       {"id": lzma.FILTER_DELTA, "dist": 5},
       {"id": lzma.FILTER_LZMA2, "preset": 7 | lzma.PRESET_EXTREME},
   ]
   with lzma.open("file.xz", "w", filters=my_filters) as f:
       f.write(b"blah blah blah")
