0.9.0:
Backwards Compatibility Notes
CFFI 1.11 or newer is now required (previous requirement was 1.8).
The primary module is now zstandard. Please change imports of zstd and zstd_cffi to import zstandard. See the README for more. Support for importing the old names will be dropped in the next release.
ZstdCompressor.read_from() and ZstdDecompressor.read_from() have been renamed to read_to_iter(). read_from() is aliased to the new name and will be deleted in a future release.
Support for Python 2.6 has been removed.
Support for Python 3.3 has been removed.
The selectivity argument to train_dictionary() has been removed, as the feature disappeared from zstd 1.3.
Support for legacy dictionaries has been removed. Cover dictionaries are now the default. train_cover_dictionary() has effectively been renamed to train_dictionary().
The allow_empty argument from ZstdCompressor.compress() has been deleted and the method now allows empty inputs to be compressed by default.
estimate_compression_context_size() has been removed. Use CompressionParameters.estimated_compression_context_size() instead.
get_compression_parameters() has been removed. Use CompressionParameters.from_level() instead.
The arguments to CompressionParameters.__init__() have changed. If you were using positional arguments before, the positions now map to different arguments. It is recommended to use keyword arguments to construct CompressionParameters instances.
TARGETLENGTH_MAX constant has been removed (it disappeared from zstandard 1.3.4).
ZstdCompressor.write_to() and ZstdDecompressor.write_to() have been renamed to ZstdCompressor.stream_writer() and ZstdDecompressor.stream_writer(), respectively. The old names are still aliased, but will be removed in the next major release.
Content sizes are written into frame headers by default (ZstdCompressor(write_content_size=True) is now the default).
CompressionParameters has been renamed to ZstdCompressionParameters for consistency with other types. The old name is an alias and will be removed in the next major release.
Bug Fixes
Fixed memory leak in ZstdCompressor.copy_stream().
Fixed memory leak in ZstdDecompressor.copy_stream().
Fixed memory leak of ZSTD_DDict instances in CFFI's ZstdDecompressor.
New Features
Bundlded zstandard library upgraded from 1.1.3 to 1.3.4. This delivers various bug fixes and performance improvements. It also gives us access to newer features.
Support for negative compression levels.
Support for long distance matching (facilitates compression ratios that approach LZMA).
Supporting for reading empty zstandard frames (with an embedded content size of 0).
Support for writing and partial support for reading zstandard frames without a magic header.
New stream_reader() API that exposes the io.RawIOBase interface (allows you to .read() from a file-like object).
Several minor features, bug fixes, and performance enhancements.
Wheels for Linux and macOS are now provided with releases.
Changes
Functions accepting bytes data now use the buffer protocol and can accept more types (like memoryview and bytearray).
Add #includes so compilation on OS X and BSDs works.
New ZstdDecompressor.stream_reader() API to obtain a read-only i/o stream of decompressed data for a source.
New ZstdCompressor.stream_reader() API to obtain a read-only i/o stream of compressed data for a source.
Renamed ZstdDecompressor.read_from() to ZstdDecompressor.read_to_iter(). The old name is still available.
Renamed ZstdCompressor.read_from() to ZstdCompressor.read_to_iter(). read_from() is still available at its old location.
Introduce the zstandard module to import and re-export the C or CFFI backend as appropriate. Behavior can be controlled via the PYTHON_ZSTANDARD_IMPORT_POLICY environment variable. See README for usage info.
Vendored version of zstd upgraded to 1.3.4.
Added module constants CONTENTSIZE_UNKNOWN and CONTENTSIZE_ERROR.
Add STRATEGY_BTULTRA compression strategy constant.
Switch from deprecated ZSTD_getDecompressedSize() to ZSTD_getFrameContentSize() replacement.
ZstdCompressor.compress() can now compress empty inputs without requiring special handling.
ZstdCompressor and ZstdDecompressor now have a memory_size() method for determining the current memory utilization of the underlying zstd primitive.
train_dictionary() has new arguments and functionality for trying multiple variations of COVER parameters and selecting the best one.
Added module constants LDM_MINMATCH_MIN, LDM_MINMATCH_MAX, and LDM_BUCKETSIZELOG_MAX.
Converted all consumers to the zstandard new advanced API, which uses ZSTD_compress_generic()
CompressionParameters.__init__ now accepts several more arguments, including support for long distance matching.
ZstdCompressionDict.__init__ now accepts a dict_type argument that controls how the dictionary should be interpreted. This can be used to force the use of content-only dictionaries or to require the presence of the dictionary magic header.
ZstdCompressionDict.precompute_compress() can be used to precompute the compression dictionary so it can efficiently be used with multiple ZstdCompressor instances.
Digested dictionaries are now stored in ZstdCompressionDict instances, created automatically on first use, and automatically reused by all ZstdDecompressor instances bound to that dictionary.
All meaningful functions now accept keyword arguments.
ZstdDecompressor.decompressobj() now accepts a write_size argument to control how much work to perform on every decompressor invocation.
ZstdCompressor.write_to() now exposes a tell(), which exposes the total number of bytes written so far.
ZstdDecompressor.stream_reader() now supports seek() when moving forward in the stream.
Removed TARGETLENGTH_MAX constant.
Added frame_header_size(data) function.
Added frame_content_size(data) function.
Consumers of ZSTD_decompress* have been switched to the new advanced decompression API.
ZstdCompressor and ZstdCompressionParams can now be constructed with negative compression levels.
ZstdDecompressor now accepts a max_window_size argument to limit the amount of memory required for decompression operations.
FORMAT_ZSTD1 and FORMAT_ZSTD1_MAGICLESS constants to be used with the format compression parameter to control whether the frame magic header is written.
ZstdDecompressor now accepts a format argument to control the expected frame format.
ZstdCompressor now has a frame_progression() method to return information about the current compression operation.
Error messages in CFFI no longer have b'' literals.
Compiler warnings and underlying overflow issues on 32-bit platforms have been fixed.
Builds in CI now build with compiler warnings as errors. This should hopefully fix new compiler warnings from being introduced.
Make ZstdCompressor(write_content_size=True) and CompressionParameters(write_content_size=True) the default.
CompressionParameters has been renamed to ZstdCompressionParameters.
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