lz4.frame sub-package¶
This sub-package is in beta testing. Ahead of version 1.0 there may be API changes, but these are expected to be minimal, if any.
This sub-package provides the capability to compress and decompress data using the LZ4 frame specification.
The frame specification is recommended for most applications. A key benefit of using the frame specification (compared to the block specification) is interoperability with other implementations.
Low level bindings for full content (de)compression¶
These functions are bindings to the LZ4 Frame API functions for compressing data into a single frame, and decompressing a full frame of data.
-
lz4.frame.
compress
()¶ compress(data, compression_level=0, block_size=0, content_checksum=0, block_linked=True, store_size=True, return_bytearray=False)
Compresses
data
returning the compressed data as a complete frame.The returned data includes a header and endmark and so is suitable for writing to a file.
Parameters: data (str, bytes or buffer-compatible object) – data to compress
Keyword Arguments: - block_size (int) –
Sepcifies the maximum blocksize to use. Options:
lz4.frame.BLOCKSIZE_DEFAULT
: the lz4 library defaultlz4.frame.BLOCKSIZE_MAX64KB
: 64 kBlz4.frame.BLOCKSIZE_MAX256KB
: 256 kBlz4.frame.BLOCKSIZE_MAX1MB
: 1 MBlz4.frame.BLOCKSIZE_MAX4MB
: 4 MB
If unspecified, will default to
lz4.frame.BLOCKSIZE_DEFAULT
which is currently equal tolz4.frame.BLOCKSIZE_MAX64KB
. - block_linked (bool) – Specifies whether to use block-linked
compression. If
True
, the compression ratio is improved, particularly for small block sizes. Default isTrue
. - compression_level (int) –
Specifies the level of compression used. Values between 0-16 are valid, with 0 (default) being the lowest compression (0-2 are the same value), and 16 the highest. Values below 0 will enable “fast acceleration”, proportional to the value. Values above 16 will be treated as 16. The following module constants are provided as a convenience:
lz4.frame.COMPRESSIONLEVEL_MIN
: Minimum compression (0, the default)lz4.frame.COMPRESSIONLEVEL_MINHC
: Minimum high-compression mode (3)lz4.frame.COMPRESSIONLEVEL_MAX
: Maximum compression (16)
- content_checksum (bool) – Specifies whether to enable checksumming
of the uncompressed content. If True, a checksum is stored at the
end of the frame, and checked during decompression. Default is
False
. - block_checksum (bool) –
Specifies whether to enable checksumming of the uncompressed content of each block. If
True
a checksum of the uncompressed data in each block in the frame is stored atthe end of each block. If present, these checksums will be used
to validate the data during decompression. The default is
False
meaning block checksums are not calculated and stored. This functionality is only supported if the underlying LZ4 library has version >= 1.8.0. Attempting to set this value toTrue
with a version of LZ4 < 1.8.0 will cause aRuntimeError
to be raised. - return_bytearray (bool) – If
True
abytearray
object will be returned. IfFalse
, a string of bytes is returned. The default isFalse
. - store_size (bool) – If
True
then the frame will include an 8-byte header field that is the uncompressed size of data included within the frame. Default isTrue
.
Returns: Compressed data
Return type: bytes or bytearray
- block_size (int) –
-
lz4.frame.
decompress
(data, return_bytearray=False, return_bytes_read=False)¶ Decompresses a frame of data and returns it as a string of bytes.
Parameters: data (str, bytes or buffer-compatible object) – data to decompress. This should contain a complete LZ4 frame of compressed data.
Keyword Arguments: - return_bytearray (bool) – If
True
a bytearray object will be returned. IfFalse
, a string of bytes is returned. The default isFalse
. - return_bytes_read (bool) – If
True
then the number of bytes read fromdata
will also be returned. Default isFalse
Returns: Uncompressed data and optionally the number of bytes read
If the
return_bytes_read
argument isTrue
this function returns a tuple consisting of:- bytes or bytearray: Uncompressed data
- int: Number of bytes consumed from
data
Return type: bytes/bytearray or tuple
- return_bytearray (bool) – If
Low level bindings for chunked content (de)compression¶
These functions are bindings to the LZ4 Frame API functions allowing piece-wise compression and decompression. Using them requires managing compression and decompression contexts manually. An alternative to using these is to use the context manager classes described in the section below.
Compression¶
-
lz4.frame.
create_compression_context
()¶ Creates a compression context object.
The compression object is required for compression operations.
Returns: A compression context Return type: cCtx
-
lz4.frame.
compress_begin
()¶ compress_begin(context, source_size=0, compression_level=0, block_size=0, content_checksum=0, content_size=1, block_linked=0, frame_type=0, auto_flush=1)
Creates a frame header from a compression context.
Parameters: context (cCtx) – A compression context.
Keyword Arguments: - block_size (int) –
Sepcifies the maximum blocksize to use. Options:
lz4.frame.BLOCKSIZE_DEFAULT
: the lz4 library defaultlz4.frame.BLOCKSIZE_MAX64KB
: 64 kBlz4.frame.BLOCKSIZE_MAX256KB
: 256 kBlz4.frame.BLOCKSIZE_MAX1MB
: 1 MBlz4.frame.BLOCKSIZE_MAX4MB
: 4 MB
If unspecified, will default to
lz4.frame.BLOCKSIZE_DEFAULT
which is currently equal tolz4.frame.BLOCKSIZE_MAX64KB
. - block_linked (bool) – Specifies whether to use block-linked
compression. If
True
, the compression ratio is improved, particularly for small block sizes. Default isTrue
. - compression_level (int) –
Specifies the level of compression used. Values between 0-16 are valid, with 0 (default) being the lowest compression (0-2 are the same value), and 16 the highest. Values below 0 will enable “fast acceleration”, proportional to the value. Values above 16 will be treated as 16. The following module constants are provided as a convenience:
lz4.frame.COMPRESSIONLEVEL_MIN
: Minimum compression (0, the default)lz4.frame.COMPRESSIONLEVEL_MINHC
: Minimum high-compression mode (3)lz4.frame.COMPRESSIONLEVEL_MAX
: Maximum compression (16)
- content_checksum (bool) – Specifies whether to enable checksumming
of the uncompressed content. If True, a checksum is stored at the
end of the frame, and checked during decompression. Default is
False
. - block_checksum (bool) –
Specifies whether to enable checksumming of the uncompressed content of each block. If
True
a checksum of the uncompressed data in each block in the frame is stored atthe end of each block. If present, these checksums will be used
to validate the data during decompression. The default is
False
meaning block checksums are not calculated and stored. This functionality is only supported if the underlying LZ4 library has version >= 1.8.0. Attempting to set this value toTrue
with a version of LZ4 < 1.8.0 will cause aRuntimeError
to be raised. - return_bytearray (bool) – If
True
abytearray
object will be returned. IfFalse
, a string of bytes is returned. The default isFalse
. - auto_flush (bool) – Enable or disable autoFlush. When autoFlush is disabled
the LZ4 library may buffer data internally until a block is full.
Default is
False
(autoFlush disabled). - source_size (int) – This optionally specifies the uncompressed size
of the data to be compressed. If specified, the size will be stored
in the frame header for use during decompression. Default is
True
- return_bytearray – If
True
a bytearray object will be returned. IfFalse
, a string of bytes is returned. Default isFalse
.
Returns: Frame header.
Return type: bytes or bytearray
- block_size (int) –
-
lz4.frame.
compress_chunk
(context, data)¶ Compresses blocks of data and returns the compressed data.
The returned data should be concatenated with the data returned from
lz4.frame.compress_begin
and any subsequent calls tolz4.frame.compress_chunk
.Parameters: - context (cCtx) – compression context
- data (str, bytes or buffer-compatible object) – data to compress
Keyword Arguments: return_bytearray (bool) – If
True
a bytearray object will be returned. IfFalse
, a string of bytes is returned. The default is False.Returns: Compressed data.
Return type: bytes or bytearray
Notes
If auto flush is disabled (
auto_flush=False
when callinglz4.frame.compress_begin
) this function may buffer and retain some or all of the compressed data for future calls tolz4.frame.compress
.
-
lz4.frame.
compress_flush
(context, end_frame=True, return_bytearray=False)¶ Flushes any buffered data held in the compression context.
This flushes any data buffed in the compression context, returning it as compressed data. The returned data should be appended to the output of previous calls to
lz4.frame.compress_chunk
.The
end_frame
argument specifies whether or not the frame should be ended. If this isTrue
and end of frame marker will be appended to the returned data. In this case, ifcontent_checksum
wasTrue
when callinglz4.frame.compress_begin
, then a checksum of the uncompressed data will also be included in the returned data.If the
end_frame
argument isTrue
, the compression context will be reset and can be re-used.Parameters: context (cCtx) – Compression context
Keyword Arguments: - end_frame (bool) – If
True
the frame will be ended. Default isTrue
. - return_bytearray (bool) – If
True
abytearray
object will be returned. IfFalse
, abytes
object is returned. The default isFalse
.
Returns: compressed data.
Return type: bytes or bytearray
Notes
If
end_frame
isFalse
but the underlying LZ4 library does not support flushing without ending the frame, aRuntimeError
will be raised.- end_frame (bool) – If
Decompression¶
-
lz4.frame.
create_decompression_context
()¶ Creates a decompression context object.
A decompression context is needed for decompression operations.
Returns: A decompression context Return type: dCtx
-
lz4.frame.
reset_decompression_context
(context)¶ Resets a decompression context object.
This is useful for recovering from an error or for stopping an unfinished decompression and starting a new one with the same context
Parameters: context (dCtx) – A decompression context
-
lz4.frame.
decompress_chunk
(context, data, max_length=-1)¶ Decompresses part of a frame of compressed data.
The returned uncompressed data should be concatenated with the data returned from previous calls to
lz4.frame.decompress_chunk
Parameters: - context (dCtx) – decompression context
- data (str, bytes or buffer-compatible object) – part of a LZ4 frame of compressed data
Keyword Arguments: - max_length (int) – if non-negative this specifies the maximum number
of bytes of uncompressed data to return. Default is
-1
. - return_bytearray (bool) – If
True
a bytearray object will be returned.IfFalse
, a string of bytes is returned. The default isFalse
.
Returns: uncompressed data, bytes read, end of frame indicator
This function returns a tuple consisting of:
- The uncompressed data as a
bytes
orbytearray
object - The number of bytes consumed from input
data
as anint
- The end of frame indicator as a
bool
.
Return type: tuple
The end of frame indicator is
True
if the end of the compressed frame has been reached, orFalse
otherwise
Retrieving frame information¶
The following function can be used to retrieve information about a compressed frame.
-
lz4.frame.
get_frame_info
(frame)¶ Given a frame of compressed data, returns information about the frame.
Parameters: frame (str, bytes or buffer-compatible object) – LZ4 compressed frame Returns: Dictionary with keys: block_size
(int): the maximum size (in bytes) of each blockblock_size_id
(int): identifier for maximum block sizecontent_checksum
(bool): specifies whether the frame- contains a checksum of the uncompressed content
content_size
(int): uncompressed size in bytes of frame contentblock_linked
(bool): specifies whether the frame contains blocks which are independently compressed (False
) or linked linked (True
)block_checksum
(bool): specifies whether each block contains a checksum of its contentsskippable
(bool): whether the block is skippable (True
) or not (False
)
Return type: dict
Helper context manager classes¶
These classes, which utilize the low level bindings to the Frame API are more convenient to use. They provide context management, and so it is not necessary to manually create and manage compression and decompression contexts.
-
class
lz4.frame.
LZ4FrameCompressor
(block_size=0, block_linked=True, compression_level=0, content_checksum=False, block_checksum=False, auto_flush=False, return_bytearray=False)¶ Create a LZ4 frame compressor object.
This object can be used to compress data incrementally.
Parameters: - block_size (int) –
Specifies the maximum blocksize to use. Options:
lz4.frame.BLOCKSIZE_DEFAULT
: the lz4 library defaultlz4.frame.BLOCKSIZE_MAX64KB
: 64 kBlz4.frame.BLOCKSIZE_MAX256KB
: 256 kBlz4.frame.BLOCKSIZE_MAX1MB
: 1 MBlz4.frame.BLOCKSIZE_MAX4MB
: 4 MB
If unspecified, will default to
lz4.frame.BLOCKSIZE_DEFAULT
which is equal tolz4.frame.BLOCKSIZE_MAX64KB
. - block_linked (bool) – Specifies whether to use block-linked
compression. If
True
, the compression ratio is improved, especially for small block sizes. IfFalse
the blocks are compressed independently. The default isTrue
. - compression_level (int) –
Specifies the level of compression used. Values between 0-16 are valid, with 0 (default) being the lowest compression (0-2 are the same value), and 16 the highest. Values above 16 will be treated as 16. Values between 4-9 are recommended. 0 is the default. The following module constants are provided as a convenience:
lz4.frame.COMPRESSIONLEVEL_MIN
: Minimum compression (0)lz4.frame.COMPRESSIONLEVEL_MINHC
: Minimum high-compression (3)lz4.frame.COMPRESSIONLEVEL_MAX
: Maximum compression (16)
- content_checksum (bool) – Specifies whether to enable checksumming of
the payload content. If
True
, a checksum of the uncompressed data is stored at the end of the compressed frame which is checked during decompression. The default isFalse
. - block_checksum (bool) – Specifies whether to enable checksumming of
the content of each block. If
True
a checksum of the uncompressed data in each block in the frame is stored at the end of each block. If present, these checksums will be used to validate the data during decompression. The default isFalse
, meaning block checksums are not calculated and stored. This functionality is only supported if the underlying LZ4 library has version >= 1.8.0. Attempting to set this value toTrue
with a version of LZ4 < 1.8.0 will cause aRuntimeError
to be raised. - auto_flush (bool) – When
False
, the LZ4 library may buffer data until a block is full. WhenTrue
no buffering occurs, and partially full blocks may be returned. The default isFalse
. - return_bytearray (bool) – When
False
abytes
object is returned from the calls to methods of this class. WhenTrue
abytearray
object will be returned. The default isFalse
.
-
begin
(source_size=0)¶ Begin a compression frame.
The returned data contains frame header information. The data returned from subsequent calls to
compress()
should be concatenated with this header.Keyword Arguments: source_size (int) – Optionally specify the total size of the uncompressed data. If specified, will be stored in the compressed frame header as an 8-byte field for later use during decompression. Default is 0 (no size stored). Returns: frame header data Return type: bytes or bytearray
-
compress
(data)¶ Compresses data and returns it.
This compresses
data
(abytes
object), returning a bytes or bytearray object containing compressed data the input.If
auto_flush
has been set toFalse
, some ofdata
may be buffered internally, for use in later calls toLZ4FrameCompressor.compress()
andLZ4FrameCompressor.flush()
.The returned data should be concatenated with the output of any previous calls to
compress()
and a single call tocompress_begin()
.Parameters: data (str, bytes or buffer-compatible object) – data to compress Returns: compressed data Return type: bytes or bytearray
-
flush
()¶ Finish the compression process.
This returns a
bytes
orbytearray
object containing any data stored in the compressor’s internal buffers and a frame footer.The LZ4FrameCompressor instance may be re-used after this method has been called to create a new frame of compressed data.
Returns: compressed data and frame footer. Return type: bytes or bytearray
-
has_context
()¶ Return whether the compression context exists.
Returns: True
if the compression context exists,False
- otherwise.
Return type: bool
-
reset
()¶ Reset the
LZ4FrameCompressor
instance.This allows the
LZ4FrameCompression
instance to be re-used after an error.
-
started
()¶ Return whether the compression frame has been started.
Returns: True
if the compression frame has been started,False
- otherwise.
Return type: bool
- block_size (int) –
-
class
lz4.frame.
LZ4FrameDecompressor
(return_bytearray=False)¶ Create a LZ4 frame decompressor object.
This can be used to decompress data incrementally.
For a more convenient way of decompressing an entire compressed frame at once, see
lz4.frame.decompress()
.Parameters: return_bytearray (bool) – When False
a bytes object is returned from the calls to methods of this class. WhenTrue
a bytearray object will be returned. The default isFalse
.-
eof
¶ True
if the end-of-stream marker has been reached.False
otherwise.Type: bool
-
unused_data
¶ Data found after the end of the compressed stream. Before the end of the frame is reached, this will be
b''
.Type: bytes
-
needs_input
¶ False
if thedecompress()
method can provide more decompressed data before requiring new uncompressed input.True
otherwise.Type: bool
-
decompress
(data, max_length=-1)¶ Decompresses part or all of an LZ4 frame of compressed data.
The returned data should be concatenated with the output of any previous calls to
decompress()
.If
max_length
is non-negative, returns at mostmax_length
bytes of decompressed data. If this limit is reached and further output can be produced, theneeds_input
attribute will be set toFalse
. In this case, the next call todecompress()
may provide data asb''
to obtain more of the output. In all cases, any unconsumed data from previous calls will be prepended to the input data.If all of the input
data
was decompressed and returned (either because this was less thanmax_length
bytes, or becausemax_length
was negative), theneeds_input
attribute will be set toTrue
.If an end of frame marker is encountered in the data during decompression, decompression will stop at the end of the frame, and any data after the end of frame is available from the
unused_data
attribute. In this case, theLZ4FrameDecompressor
instance is reset and can be used for further decompression.Parameters: data (str, bytes or buffer-compatible object) – compressed data to decompress Keyword Arguments: max_length (int) – If this is non-negative, this method returns at most max_length
bytes of decompressed data.Returns: Uncompressed data Return type: bytes
-
reset
()¶ Reset the decompressor state.
This is useful after an error occurs, allowing re-use of the instance.
-
Reading and writing compressed files¶
These provide capability for reading and writing of files using LZ4 compressed frames. These are designed to be drop in replacements for the LZMA, BZ2 and Gzip equivalent functionalities in the Python standard library.
-
lz4.frame.
open
(filename, mode='rb', encoding=None, errors=None, newline=None, block_size=0, block_linked=True, compression_level=0, content_checksum=False, block_checksum=False, auto_flush=False, return_bytearray=False, source_size=0)¶ Open an LZ4Frame-compressed file in binary or text mode.
filename
can be either an actual file name (given as a str, bytes, or PathLike 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'r'
,'rb'
(default),'w'
,'wb'
,'x'
,'xb'
,'a'
, or'ab'
for binary mode, or'rt'
,'wt'
,'xt'
, or'at'
for text mode.For binary mode, this function is equivalent to the
LZ4FrameFile
constructor:LZ4FrameFile(filename, mode, ...)
.For text mode, an
LZ4FrameFile
object is created, and wrapped in anio.TextIOWrapper
instance with the specified encoding, error handling behavior, and line ending(s).Parameters: filename (str, bytes, os.PathLike) – file name or file object to open
Keyword Arguments: - mode (str) – mode for opening the file
- encoding (str) – the name of the encoding that will be used for
encoding/deconging the stream. It defaults to
locale.getpreferredencoding(False)
. Seeio.TextIOWrapper
for further details. - errors (str) – specifies how encoding and decoding errors are to be
handled. See
io.TextIOWrapper
for further details. - newline (str) – controls how line endings are handled. See
io.TextIOWrapper
for further details. - return_bytearray (bool) – When
False
a bytes object is returned from the calls to methods of this class. WhenTrue
a bytearray object will be returned. The default isFalse
. - source_size (int) – Optionally specify the total size of the uncompressed data. If specified, will be stored in the compressed frame header as an 8-byte field for later use during decompression. Default is 0 (no size stored). Only used for writing compressed files.
- block_size (int) – Compressor setting. See
lz4.frame.LZ4FrameCompressor
. - block_linked (bool) – Compressor setting. See
lz4.frame.LZ4FrameCompressor
. - compression_level (int) – Compressor setting. See
lz4.frame.LZ4FrameCompressor
. - content_checksum (bool) – Compressor setting. See
lz4.frame.LZ4FrameCompressor
. - block_checksum (bool) – Compressor setting. See
lz4.frame.LZ4FrameCompressor
. - auto_flush (bool) – Compressor setting. See
lz4.frame.LZ4FrameCompressor
.
-
class
lz4.frame.
LZ4FrameFile
(filename=None, mode='r', block_size=0, block_linked=True, compression_level=0, content_checksum=False, block_checksum=False, auto_flush=False, return_bytearray=False, source_size=0)¶ A file object providing transparent LZ4F (de)compression.
An LZ4FFile can act as a wrapper for an existing file object, or refer directly to a named file on disk.
Note that LZ4FFile provides a binary file interface - data read is returned as bytes, and data to be written must be given as bytes.
When opening a file for writing, the settings used by the compressor can be specified. The underlying compressor object is
lz4.frame.LZ4FrameCompressor
. See the docstrings for that class for details on compression options.Parameters: filename (str, bytes, PathLike, file object) – can be either an actual file name (given as a str, bytes, or PathLike object), in which case the named file is opened, or it can be an existing file object to read from or write to.
Keyword Arguments: - mode (str) – mode can be
'r'
for reading (default),'w'
for (over)writing,'x'
for creating exclusively, or'a'
for appending. These can equivalently be given as'rb'
,'wb'
,'xb'
and'ab'
respectively. - return_bytearray (bool) – When
False
a bytes object is returned from the calls to methods of this class. WhenTrue
abytearray
object will be returned. The default isFalse
. - source_size (int) – Optionally specify the total size of the
uncompressed data. If specified, will be stored in the compressed
frame header as an 8-byte field for later use during decompression.
Default is
0
(no size stored). Only used for writing compressed files. - block_size (int) – Compressor setting. See
lz4.frame.LZ4FrameCompressor
. - block_linked (bool) – Compressor setting. See
lz4.frame.LZ4FrameCompressor
. - compression_level (int) – Compressor setting. See
lz4.frame.LZ4FrameCompressor
. - content_checksum (bool) – Compressor setting. See
lz4.frame.LZ4FrameCompressor
. - block_checksum (bool) – Compressor setting. See
lz4.frame.LZ4FrameCompressor
. - auto_flush (bool) – Compressor setting. See
lz4.frame.LZ4FrameCompressor
.
-
close
()¶ Flush and close the file.
May be called more than once without error. Once the file is closed, any other operation on it will raise a ValueError.
-
closed
¶ Returns
True
if this file is closed.Returns: True
if the file is closed,False
otherwise.Return type: bool
-
fileno
()¶ Return the file descriptor for the underlying file.
Returns: file descriptor for file. Return type: file object
-
flush
()¶ Flush the file, keeping it open.
May be called more than once without error. The file may continue to be used normally after flushing.
-
peek
(size=-1)¶ Return buffered data without advancing the file position.
Always returns at least one byte of data, unless at EOF. The exact number of bytes returned is unspecified.
Returns: uncompressed data Return type: bytes
-
read
(size=-1)¶ Read up to
size
uncompressed bytes from the file.If
size
is negative or omitted, read untilEOF
is reached. Returnsb''
if the file is already atEOF
.Parameters: size (int) – If non-negative, specifies the maximum number of uncompressed bytes to return. Returns: uncompressed data Return type: bytes
-
read1
(size=-1)¶ Read up to
size
uncompressed bytes.This method tries to avoid making multiple reads from the underlying stream.
This method reads up to a buffer’s worth of data if
size
is negative.Returns
b''
if the file is at EOF.Parameters: size (int) – If non-negative, specifies the maximum number of uncompressed bytes to return. Returns: uncompressed data Return type: bytes
-
readable
()¶ Return whether the file was opened for reading.
Returns: True
if the file was opened for reading,False
- otherwise.
Return type: bool
-
readline
(size=-1)¶ Read a line of uncompressed bytes from the file.
The terminating newline (if present) is retained. If size is non-negative, no more than size bytes will be read (in which case the line may be incomplete). Returns b’’ if already at EOF.
Parameters: size (int) – If non-negative, specifies the maximum number of uncompressed bytes to return. Returns: uncompressed data Return type: bytes
-
seek
(offset, whence=0)¶ Change the file position.
The new position is specified by
offset
, relative to the position indicated bywhence
. Possible values forwhence
are:io.SEEK_SET
or 0: start of stream (default): offset must not be negativeio.SEEK_CUR
or 1: current stream positionio.SEEK_END
or 2: end of stream; offset must not be positive
Returns the new file position.
Note that seeking is emulated, so depending on the parameters, this operation may be extremely slow.
Parameters: - offset (int) – new position in the file
- whence (int) – position with which
offset
is measured. Allowed values are 0, 1, 2. The default is 0 (start of stream).
Returns: new file position
Return type: int
-
seekable
()¶ Return whether the file supports seeking.
Returns: True
if the file supports seeking,False
otherwise.Return type: bool
-
tell
()¶ Return the current file position.
Parameters: None – Returns: file position Return type: int
-
writable
()¶ Return whether the file was opened for writing.
Returns: True
if the file was opened for writing,False
- otherwise.
Return type: bool
-
write
(data)¶ Write a bytes object to the file.
Returns the number of uncompressed bytes written, which is always the length of data in bytes. Note that due to buffering, the file on disk may not reflect the data written until close() is called.
Parameters: data (bytes) – uncompressed data to compress and write to the file Returns: the number of uncompressed bytes written to the file Return type: int
- mode (str) – mode can be
Module attributes¶
A number of module attributes are defined for convenience. These are detailed below.
Compression level¶
The following module attributes can be used when setting the
compression_level
argument.
-
lz4.frame.
COMPRESSIONLEVEL_MIN
¶ Specifier for the minimum compression level.
Specifying
compression_level=lz4.frame.COMPRESSIONLEVEL_MIN
will instruct the LZ4 library to use a compression level of 0
-
lz4.frame.
COMPRESSIONLEVEL_MINHC
¶ Specifier for the minimum compression level for high compression mode.
Specifying
compression_level=lz4.frame.COMPRESSIONLEVEL_MINHC
will instruct the LZ4 library to use a compression level of 3, the minimum for the high compression mode.
-
lz4.frame.
COMPRESSIONLEVEL_MAX
¶ Specifier for the maximum compression level.
Specifying
compression_level=lz4.frame.COMPRESSIONLEVEL_MAX
will instruct the LZ4 library to use a compression level of 16, the highest compression level available.
Block size¶
The following attributes can be used when setting the block_size
argument.
-
lz4.frame.
BLOCKSIZE_DEFAULT
¶ Specifier for the default block size.
Specifying
block_size=lz4.frame.BLOCKSIZE_DEFAULT
will instruct the LZ4 library to use the default maximum blocksize. This is currently equivalent tolz4.frame.BLOCKSIZE_MAX64KB
-
lz4.frame.
BLOCKSIZE_MAX64KB
¶ Specifier for a maximum block size of 64 kB.
Specifying
block_size=lz4.frame.BLOCKSIZE_MAX64KB
will instruct the LZ4 library to create blocks containing a maximum of 64 kB of uncompressed data.
-
lz4.frame.
BLOCKSIZE_MAX256KB
¶ Specifier for a maximum block size of 256 kB.
Specifying
block_size=lz4.frame.BLOCKSIZE_MAX256KB
will instruct the LZ4 library to create blocks containing a maximum of 256 kB of uncompressed data.
-
lz4.frame.
BLOCKSIZE_MAX1MB
¶ Specifier for a maximum block size of 1 MB.
Specifying
block_size=lz4.frame.BLOCKSIZE_MAX1MB
will instruct the LZ4 library to create blocks containing a maximum of 1 MB of uncompressed data.
-
lz4.frame.
BLOCKSIZE_MAX4MB
¶ Specifier for a maximum block size of 4 MB.
Specifying
block_size=lz4.frame.BLOCKSIZE_MAX4MB
will instruct the LZ4 library to create blocks containing a maximum of 4 MB of uncompressed data.