lzma — Compression using the LZMA algorithm¶New in version 3.3.
Source code: 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
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.
lzma.LZMAError¶This exception is raised when an error occurs during compression or decompression, or while initializing the compressor/decompressor state.
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, bytes or path-like 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 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).
Changed in version 3.4: Added support for the "x", "xb" and "xt" modes.
Changed in version 3.6: Accepts a path-like object.
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,
bytes or path-like 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, "x" for exclusive creation, or "a" for appending. These
can equivalently be given as "rb", "wb", "xb" 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).
Changed in version 3.4: Added support for the "x" and "xb" modes.
Changed in version 3.5: The read() method now accepts an argument of
None.
Changed in version 3.6: Accepts a path-like object.
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.FORMAT_ALONE: The legacy .lzma container format..xz – it does not support integrity
checks or multiple filters.FORMAT_RAW: A raw data stream, not using any container format.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().
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, max_length=-1)¶Decompress data (a bytes-like object), returning
uncompressed data as bytes. 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().
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 needs_input attribute will
be set to False. In this case, the next call to
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 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 unused_data attribute.
Changed in version 3.5: Added the max_length parameter.
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"".
needs_input¶False if the decompress() method can provide more
decompressed data before requiring new uncompressed input.
New in version 3.5.
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.
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.
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:
FILTER_LZMA1 (for use with FORMAT_ALONE)FILTER_LZMA2 (for use with FORMAT_XZ and FORMAT_RAW)FILTER_DELTAFILTER_X86FILTER_IA64FILTER_ARMFILTER_ARMTHUMBFILTER_POWERPCFILTER_SPARCA 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:MODE_FASTorMODE_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, orMF_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")