Release notes



  • Speed up isinstance checks of numcodecs.ndarray_like.NDArrayLike, numcodecs.ndarray_like.DType and numcodecs.ndarray_like.FlagsObj. By Andreas Poehlmann, #379.








Bug fixes




  • c-blosc upgrade 1.18.1 -> 1.21.0. Warning: this temporarily removes support for snappy compression! By kindjacket, #283.

  • Fix an ImportError with Blosc on Android. By Daniel Jewell, #284.




  • Add support for Python 3.9 and Update GitHub Actions. By Jackson Maxfield Brown, #270.

  • Remove support for Python 3.5 which is end of life. While the code base might still be compatible; the source dist and wheel are marked as Python 3.6+ and pip will not install them. Continuous integration on Python 3.5 has been disabled. By Matthias Bussonnier, #266 and #267.









  • The encoding format used by the JSON and MsgPack codecs has been changed to resolve an issue with correctly encoding and decoding some object arrays. Now the encoded data includes the original shape of the array, which enables the correct shape to be restored on decoding. The previous encoding format is still supported, so that any data encoded using a previous version of numcodecs can still be read. Thus no changes to user code and applications should be required, other than upgrading numcodecs. By Jerome Kelleher; #74, #75.

  • Updated the msgpack dependency (by Jerome Kelleher; #74, #75).

  • Added support for ppc64le architecture by updating from upstream (by Anand S; #82).

  • Allow numcodecs.blosc.Blosc compressor to run on systems where locks are not present (by Marcus Kinsella, #83; and Tom White, #93).

  • Drop Python 3.4 (by John Kirkham; #89).

  • Add Python 3.7 (by John Kirkham; #92).

  • Add codec numcodecs.gzip.GZip to replace gzip alias for zlib, which was incorrect (by Jan Funke; #87; and John Kirkham, #134).

  • Corrects handling of NaT in datetime64 and timedelta64 in various compressors (by John Kirkham; #127, #131).

  • Improvements to the compatibility layer used for normalising inputs to encode and decode methods in most codecs. This removes unnecessary memory copies for some codecs, and also simplifies the implementation of some codecs, improving code readability and maintainability. By John Kirkham and Alistair Miles; #119, #121, #128.

  • Return values from encode() and decode() methods are now returned as numpy arrays for consistency across codecs. By John Kirkham, #136.

  • Improvements to handling of errors in the numcodecs.blosc.Blosc and numcodecs.lz4.LZ4 codecs when the maximum allowed size of an input buffer is exceeded. By Jerome Kelleher, #80, #81.


  • The bundled c-blosc sources have been upgraded to version 1.14.3 (#72).


  • The bundled c-blosc sources have been upgraded to version 1.14.0 (#71).


  • The test suite has been migrated to use pytest instead of nosetests (#61, #62).

  • The bundled c-blosc library has been updated to version 1.13.4 (#63, #64).


  • Add support for encoding None values in VLen… codecs (#59).


  • Fixed a compatibility issue with the Zlib codec to ensure it can handle bytearray objects under Python 2.7 (#57).

  • Restricted the numcodecs.categorize.Categorize codec to object (‘O’) and unicode (‘U’) dtypes and disallowed bytes (‘S’) dtypes because these do not round-trip through JSON configuration.



  • Resolved an issue where providing an array with dtype object as the destination when decoding could cause segfaults with some codecs (#55).



  • Revert the default shuffle argument to SHUFFLE (byte shuffle) for the numcodecs.blosc.Blosc codec for compatibility and consistency with previous code.


  • The numcodecs.blosc.Blosc codec has been made robust for usage in both multithreading and multiprocessing programs, regardless of whether Blosc has been configured to use multiple threads internally or not (#41, #42).

  • The numcodecs.blosc.Blosc codec now supports an AUTOSHUFFLE argument when encoding (compressing) which activates bit- or byte-shuffle depending on the itemsize of the incoming buffer (#37, #42). This is also now the default.

  • The numcodecs.blosc.Blosc codec now raises an exception when an invalid compressor name is provided under all circumstances (#40, #42).

  • The bundled version of the c-blosc library has been upgraded to version 1.12.1 (#45, #42).

  • An improvement has been made to the system detection capabilities during compilation of C extensions (by Prakhar Goel; #36, #38).

  • Arrays with datetime64 or timedelta64 can now be passed directly to compressor codecs (#39, #46).


The bundled c-blosc library has been upgraded to version 1.11.3 (#34, #35).


New codecs:

Other changes:

Maintenance work:

  • A data fixture has been added to the test suite to add some protection against changes to codecs that break backwards-compatibility with data encoded using a previous release of numcodecs (#30, #33).


This release includes a small modification to the script to provide greater control over how compiler options for different instruction sets are configured (#24, #27).


New codecs:

Other new features:

  • The numcodecs.lzma.LZMA codec is now supported on Python 2.7 if backports.lzma is installed (John Kirkham; #11, #13).

  • The bundled c-blosc library has been upgraded to version 1.11.2 (#10, #18).

  • An option has been added to the numcodecs.blosc.Blosc codec to allow the block size to be manually configured (#9, #19).

  • The representation string for the numcodecs.blosc.Blosc codec has been tweaked to help with understanding the shuffle option (#4, #19).

  • Options have been added to manually control how the C extensions are built regardless of the architecture of the system on which the build is run. To disable support for AVX2 set the environment variable “DISABLE_NUMCODECS_AVX2”. To disable support for SSE2 set the environment variable “DISABLE_NUMCODECS_SSE2”. To disable C extensions altogether set the environment variable “DISABLE_NUMCODECS_CEXT” (#24, #26).

Maintenance work:

  • CI tests now run under Python 3.6 as well as 2.7, 3.4, 3.5 (#16, #17).

  • Test coverage is now monitored via coveralls (#15, #20).


Fixed project description in


First release. This version is a port of the codecs module from Zarr 2.1.0. The following changes have been made from the original Zarr module:

  • Codec classes have been re-organized into separate modules, mostly one per codec class, for ease of maintenance.

  • Two new codec classes have been added based on 32-bit checksums: numcodecs.checksum32.CRC32 and numcodecs.checksum32.Adler32.

  • The Blosc extension has been refactored to remove code duplications related to handling of buffer compatibility.