Backwards Compatibility Notes

• Support for Python 2.7 has been dropped. Python 3.5 is now the
  minimum required Python version. (#109)
• train_dictionary() now uses the fastcover training mechanism
  (as opposed to cover). Some parameter values that worked with the old
  mechanism may not work with the new one. e.g. d must be 6 or 8
  if it is defined.
• train_dictionary() now always calls
  ZDICT_optimizeTrainFromBuffer_fastCover() instead of different APIs
  depending on which arguments were passed.
• The names of various Python modules have been changed. The C extension
  is now built as zstandard.backend_c instead of zstd. The
  CFFI extension module is now built as zstandard._cffi instead of
  _zstd_cffi. The CFFI backend is now zstandard.backend_cffi instead
  of zstandard.cffi.
• ZstdDecompressionReader.seekable() now returns False instead of
  True because not all seek operations are supported and some Python
  code in the wild keys off this value to determine if seek() can be
  called for all scenarios.
• ZstdDecompressionReader.seek() now raises OSError instead of
  ValueError when the seek cannot be fulfilled. (#107)
• ZstdDecompressionReader.readline() and
  ZstdDecompressionReader.readlines() now accept an integer argument.
  This makes them conform with the IO interface. The methods still raise
  io.UnsupportedOperation.
• ZstdCompressionReader.__enter__ and ZstdDecompressionReader.__enter__
  now raise ValueError if the instance was already closed.
• The deprecated overlap_size_log attribute on ZstdCompressionParameters
  instances has been removed. The overlap_log attribute should be used
  instead.
• The deprecated overlap_size_log argument to ZstdCompressionParameters
  has been removed. The overlap_log argument should be used instead.
• The deprecated ldm_hash_every_log attribute on
  ZstdCompressionParameters instances has been removed. The
  ldm_hash_rate_log attribute should be used instead.
• The deprecated ldm_hash_every_log argument to
  ZstdCompressionParameters has been removed. The ldm_hash_rate_log
  argument should be used instead.
• The deprecated CompressionParameters type alias to
  ZstdCompressionParamaters has been removed. Use
  ZstdCompressionParameters.
• The deprecated aliases ZstdCompressor.read_from() and
  ZstdDecompressor.read_from() have been removed. Use the corresponding
  read_to_iter() methods instead.
• The deprecated aliases ZstdCompressor.write_to() and
  ZstdDecompressor.write_to() have been removed. Use the corresponding
  stream_writer() methods instead.
• ZstdCompressor.copy_stream(), ZstdCompressorIterator.__next__(),
  and ZstdDecompressor.copy_stream() now raise the original exception
  on error calling the source stream's read() instead of raising
  ZstdError. This only affects the C backend.
• ZstdDecompressionObj.flush() now returns bytes instead of
  None. This makes it behave more similarly to flush() methods
  for similar types in the Python standard library. (#78)
• ZstdCompressionWriter.__exit__() now always calls close().
  Previously, close() would not be called if the context manager
  raised an exception. The old behavior was inconsistent with other
  stream types in this package and with the behavior of Python's
  standard library IO types. (#86)
• Distribution metadata no longer lists cffi as an install_requires
  except when running on PyPy. Instead, cffi is listed as an
  extras_require.
• ZstdCompressor.stream_reader() and ZstdDecompressor.stream_reader()
  now default to closing the source stream when the instance is itself
  closed. To change this behavior, pass closefd=False. (#76)
• The CFFI backend now defines
  ZstdCompressor.multi_compress_to_buffer() and
  ZstdDecompressor.multi_decompress_to_buffer(). However, they
  raise NotImplementedError, as they are not yet implemented.
• The CFFI backend now exposes the types ZstdCompressionChunker,
  ZstdCompressionObj, ZstdCompressionReader,
  ZstdCompressionWriter, ZstdDecompressionObj,
  ZstdDecompressionReader, and ZstdDecompressionWriter as
  symbols on the zstandard module.
• The CFFI backend now exposes the types BufferSegment,
  BufferSegments, BufferWithSegments, and
  BufferWithSegmentsCollection. However, they are not implemented.
• ZstdCompressionWriter.flush() now calls flush() on the inner stream
  if such a method exists. However, when close() itself calls
  self.flush(), flush() is not called on the inner stream.
• ZstdDecompressionWriter.close() no longer calls flush() on
  the inner stream. However, ZstdDecompressionWriter.flush() still
  calls flush() on the inner stream.
• ZstdCompressor.stream_writer() and ZstdDecompressor.stream_writer()
  now have their write_return_read argument default to True.
  This brings the behavior of write() in compliance with the
  io.RawIOBase interface by default. The argument may be removed
  in a future release.
• ZstdCompressionParameters no longer exposes a compression_strategy
  property. Its constructor no longer accepts a compression_strategy
  argument. Use the strategy property/argument instead.

Bug Fixes

• Fix a memory leak in stream_reader decompressor when reader is closed
  before reading everything. (Patch by Pierre Fersing.)
• The C backend now properly checks for errors after calling IO methods
  on inner streams in various methods. ZstdCompressionWriter.write()
  now catches exceptions when calling the inner stream's write().
  ZstdCompressionWriter.flush() on inner stream's write().
  ZstdCompressor.copy_stream() on dest stream's write().
  ZstdDecompressionWriter.write() on inner stream's write().
  ZstdDecompressor.copy_stream() on dest stream's write(). (#102)

Changes

• Bundled zstandard library upgraded from 1.4.5 to 1.4.8.
• The bundled zstandard library is now using the single C source file
  distribution. The 2 main header files are still present, as these are
  needed by CFFI to generate the CFFI bindings.
• PyBuffer instances are no longer checked to be C contiguous and
  have a single dimension. The former was redundant with what
  PyArg_ParseTuple() already did and the latter is not necessary
  in practice because very few extension modules create buffers with
  more than 1 dimension. (#124)
• Added Python typing stub file for the zstandard module. (#120)
• The make_cffi.py script should now respect the CC environment
  variable for locating the compiler. (#103)
• CI now properly uses the cffi backend when running all tests.
• train_dictionary() has been rewritten to use the fastcover APIs
  and to consistently call ZDICT_optimizeTrainFromBuffer_fastCover()
  instead of different C APIs depending on what arguments were passed.
  The function also now accepts arguments f, split_point, and
  accel, which are parameters unique to fastcover.
• CI now tests and builds wheels for Python 3.9.
• zstd.c file renamed to c-ext/backend_c.c.
• All built/installed Python modules are now in the zstandard
  package. Previously, there were modules in other packages. (#115)
• C source code is now automatically formatted with clang-format.
• ZstdCompressor.stream_writer(), ZstdCompressor.stream_reader(),
  ZstdDecompressor.stream_writer(), and
  ZstdDecompressor.stream_reader() now accept a closefd
  argument to control whether the underlying stream should be closed
  when the ZstdCompressionWriter, ZstdCompressReader,
  ZstdDecompressionWriter, or ZstdDecompressionReader is closed.
  (#76)
• There is now a zstandard.open() function for returning a file
  object with zstd (de)compression. (#64)
• The zstandard module now exposes a backend_features
  attribute containing a set of strings denoting optional features
  present in that backend. This can be used to sniff feature support
  by performing a string lookup instead of sniffing for API presence
  or behavior.
• Python docstrings have been moved from the C backend to the CFFI
  backend. Sphinx docs have been updated to generate API documentation
  via the CFFI backend. Documentation for Python APIs is now fully
  defined via Python docstrings instead of spread across Sphinx ReST
  files and source code.
• ZstdCompressionParameters now exposes a strategy property.
• There are now compress() and decompress() convenience functions
  on the zstandard module. These are simply wrappers around the
  corresponding APIs on ZstdCompressor and ZstdDecompressor.