.. module:: lzma :synopsis: A Python wrapper for the liblzma compression library.
.. moduleauthor:: Nadeem Vawda <nadeem.vawda@gmail.com>
.. sectionauthor:: Nadeem Vawda <nadeem.vawda@gmail.com>
.. versionadded:: 3.3
Source code: :source:`Lib/lzma.py`
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
:program:`xz` utility, as well as raw compressed streams.
The interface provided by this module is very similar to that of the :mod:`bz2` module. However, note that :class:`LZMAFile` is not thread-safe, unlike :class:`bz2.BZ2File`, so if you need to use a single :class:`LZMAFile` instance from multiple threads, it is necessary to protect it with a lock.
.. exception:: LZMAError This exception is raised when an error occurs during compression or decompression, or while initializing the compressor/decompressor state.
.. function:: 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 :term:`file object`. The *filename* argument can be either an actual file name (given as a :class:`str`, :class:`bytes` or :term:`path-like <path-like object>` 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"``, ``"x"``, ``"xb"``, ``"a"`` or ``"ab"`` for binary mode, or ``"rt"``, ``"wt"``, ``"xt"``, 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 :class:`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 :class:`LZMACompressor`. For binary mode, this function is equivalent to the :class:`LZMAFile` constructor: ``LZMAFile(filename, mode, ...)``. In this case, the *encoding*, *errors* and *newline* arguments must not be provided. For text mode, a :class:`LZMAFile` object is created, and wrapped in an :class:`io.TextIOWrapper` instance with the specified encoding, error handling behavior, and line ending(s). .. versionchanged:: 3.4 Added support for the ``"x"``, ``"xb"`` and ``"xt"`` modes. .. versionchanged:: 3.6 Accepts a :term:`path-like object`.
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 :func:`compress`.
The format argument specifies what container format should be used. Possible values are:
.xz container format..lzma container format..xz -- it does not support integrity
checks or multiple filters.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:
If the specified check is not supported, an :class:`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
:const:`PRESET_EXTREME`. If neither preset nor filters are given, the
default behavior is to use :const:`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
:class:`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 :ref:`filter-chain-specs` for details.
.. method:: compress(data) Compress *data* (a :class:`bytes` object), returning a :class:`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 :meth:`compress` and :meth:`flush`. The returned data should be concatenated with the output of any previous calls to :meth:`compress`.
.. method:: flush() Finish the compression process, returning a :class:`bytes` object containing any data stored in the compressor's internal buffers. The compressor cannot be used after this method has been called.
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 :func:`decompress`.
The format argument specifies the container format that should be used. The
default is :const:`FORMAT_AUTO`, which can decompress both .xz and
.lzma files. Other possible values are :const:`FORMAT_XZ`,
:const:`FORMAT_ALONE`, and :const:`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 :class:`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 :const:`FORMAT_RAW`, but should not be used for other formats. See :ref:`filter-chain-specs` for more information about filter chains.
Note
This class does not transparently handle inputs containing multiple compressed streams, unlike :func:`decompress` and :class:`LZMAFile`. To decompress a multi-stream input with :class:`LZMADecompressor`, you must create a new decompressor for each stream.
.. method:: decompress(data, max_length=-1) Decompress *data* (a :term:`bytes-like object`), returning uncompressed data as bytes. Some of *data* may be buffered internally, for use in later calls to :meth:`decompress`. The returned data should be concatenated with the output of any previous calls to :meth:`decompress`. If *max_length* is nonnegative, returns at most *max_length* bytes of decompressed data. If this limit is reached and further output can be produced, the :attr:`~.needs_input` attribute will be set to ``False``. In this case, the next call to :meth:`~.decompress` may provide *data* as ``b''`` to obtain more of the output. If all of the input data was decompressed and returned (either because this was less than *max_length* bytes, or because *max_length* was negative), the :attr:`~.needs_input` attribute will be set to ``True``. Attempting to decompress data after the end of stream is reached raises an `EOFError`. Any data found after the end of the stream is ignored and saved in the :attr:`~.unused_data` attribute. .. versionchanged:: 3.5 Added the *max_length* parameter.
.. attribute:: check The ID of the integrity check used by the input stream. This may be :const:`CHECK_UNKNOWN` until enough of the input has been decoded to determine what integrity check it uses.
.. attribute:: eof ``True`` if the end-of-stream marker has been reached.
.. attribute:: unused_data Data found after the end of the compressed stream. Before the end of the stream is reached, this will be ``b""``.
.. attribute:: needs_input ``False`` if the :meth:`.decompress` method can provide more decompressed data before requiring new uncompressed input. .. versionadded:: 3.5
.. function:: compress(data, format=FORMAT_XZ, check=-1, preset=None, filters=None) Compress *data* (a :class:`bytes` object), returning the compressed data as a :class:`bytes` object. See :class:`LZMACompressor` above for a description of the *format*, *check*, *preset* and *filters* arguments.
.. function:: decompress(data, format=FORMAT_AUTO, memlimit=None, filters=None) Decompress *data* (a :class:`bytes` object), returning the uncompressed data as a :class:`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 :class:`LZMADecompressor` above for a description of the *format*, *memlimit* and *filters* arguments.
.. function:: is_check_supported(check) Return ``True`` if the given integrity check is supported on this system. :const:`CHECK_NONE` and :const:`CHECK_CRC32` are always supported. :const:`CHECK_CRC64` and :const:`CHECK_SHA256` may be unavailable if you are using a version of :program:`liblzma` that was compiled with a limited feature set.
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:
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 sumlc + lpmust be at most 4.pb: Number of position bits; must be at most 4.mode: :const:`MODE_FAST` or :const:`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 -- :const:`MF_HC3`, :const:`MF_HC4`, :const:`MF_BT2`, :const:`MF_BT3`, or :const:`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 supports 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.
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")
此处可能存在不合适展示的内容,页面不予展示。您可通过相关编辑功能自查并修改。
如您确认内容无涉及 不当用语 / 纯广告导流 / 暴力 / 低俗色情 / 侵权 / 盗版 / 虚假 / 无价值内容或违法国家有关法律法规的内容,可点击提交进行申诉,我们将尽快为您处理。