Numcodecs is a Python package providing buffer compression and transformation codecs for use in data storage and communication applications. These include:

  • Compression codecs, e.g., Zlib, BZ2, LZMA, ZFPY and Blosc.

  • Pre-compression filters, e.g., Delta, Quantize, FixedScaleOffset, PackBits, Categorize.

  • Integrity checks, e.g., CRC32, Adler32.

All codecs implement the same API, allowing codecs to be organized into pipelines in a variety of ways.

If you have a question, find a bug, would like to make a suggestion or contribute code, please raise an issue on GitHub.


Numcodecs depends on NumPy. It is generally best to install NumPy first using whatever method is most appropriate for you operating system and Python distribution.

Install from PyPI:

$ pip install numcodecs

Alternatively, install via conda:

$ conda install -c conda-forge numcodecs

Numcodecs includes a C extension providing integration with the Blosc library. Wheels are available for most platforms.

Installing a wheel or via conda will install a pre-compiled binary distribution. However, if you have a newer CPU that supports the AVX2 instruction set (e.g., Intel Haswell, Broadwell or Skylake) then installing via pip is preferable, because you can compile the Blosc library from source with optimisations for AVX2.:

$ pip install -v --no-cache-dir --no-binary numcodecs numcodecs

Note that if you compile the C extensions on a machine with AVX2 support you probably then cannot use the same binaries on a machine without AVX2.

If you specifically want to disable AVX2 or SSE2 when compiling, you can use the following environment variables:


To work with Numcodecs source code in development, clone the repository from GitHub and then install in editable mode using pip.:

$ git clone --recursive
$ cd numcodecs
$ pip install -e .[test,msgpack,zfpy]

Note: if you prefer to use the GitHub CLI gh you will need to append -- --recurse-submodules to the clone command to everything works properly.

To verify that Numcodecs has been fully installed (including the Blosc extension) run the test suite:

$ pytest -v



The following people have contributed to the development of NumCodecs by contributing code, documentation, code reviews, comments and/or ideas:

Numcodecs bundles the c-blosc library.

Development of this package is supported by the MRC Centre for Genomics and Global Health.

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