Usage

hdf5plugin allows using additional HDF5 compression filters with h5py for reading and writing compressed datasets.

Read compressed datasets

In order to read compressed dataset with h5py, use:

import hdf5plugin

It registers hdf5plugin supported compression filters with the HDF5 library used by h5py. Hence, HDF5 compressed datasets can be read as any other dataset (see h5py documentation).

Write compressed datasets

As for reading compressed datasets, import hdf5plugin is required to enable the supported compression filters.

To create a compressed dataset use h5py.Group.create_dataset and set the compression and compression_opts arguments.

hdf5plugin provides helpers to prepare those compression options: Bitshuffle, Blosc, BZip2, FciDecomp, LZ4, SZ, SZ3, Zfp, Zstd.

Sample code:

import numpy
import h5py
import hdf5plugin

# Compression
f = h5py.File('test.h5', 'w')
f.create_dataset('data', data=numpy.arange(100), **hdf5plugin.LZ4())
f.close()

# Decompression
f = h5py.File('test.h5', 'r')
data = f['data'][()]
f.close()

Relevant h5py documentation: Filter pipeline and Chunked Storage.

Bitshuffle

class hdf5plugin.Bitshuffle(nelems=0, cname=None, clevel=3, lz4=None)

h5py.Group.create_dataset’s compression arguments for using bitshuffle filter.

It can be passed as keyword arguments:

f = h5py.File('test.h5', 'w')
f.create_dataset(
    'bitshuffle_with_lz4',
    data=numpy.arange(100),
    **hdf5plugin.Bitshuffle(nelems=0, lz4=True))
f.close()
Parameters:
  • nelems (int) – The number of elements per block. It needs to be divisible by eight (default is 0, about 8kB per block) Default: 0 (for about 8kB per block).

  • cname (str) – lz4 (default), none, zstd

  • clevel (int) – Compression level, used only for zstd compression. Can be negative, and must be below or equal to 22 (maximum compression). Default: 3.

filter_id = 32008
filter_name = 'bshuf'

Blosc

class hdf5plugin.Blosc(cname='lz4', clevel=5, shuffle=1)

h5py.Group.create_dataset’s compression arguments for using blosc filter.

It can be passed as keyword arguments:

f = h5py.File('test.h5', 'w')
f.create_dataset(
    'blosc_byte_shuffle_blosclz',
    data=numpy.arange(100),
    **hdf5plugin.Blosc(cname='blosclz', clevel=9, shuffle=hdf5plugin.Blosc.SHUFFLE))
f.close()
Parameters:
  • cname (str) – blosclz, lz4 (default), lz4hc, zlib, zstd Optional: snappy, depending on compilation (requires C++11).

  • clevel (int) – Compression level from 0 (no compression) to 9 (maximum compression). Default: 5.

  • shuffle (int) – One of: - Blosc.NOSHUFFLE (0): No shuffle - Blosc.SHUFFLE (1): byte-wise shuffle (default) - Blosc.BITSHUFFLE (2): bit-wise shuffle

BITSHUFFLE = 2

Flag to enable bit-wise shuffle pre-compression filter

NOSHUFFLE = 0

Flag to disable data shuffle pre-compression filter

SHUFFLE = 1

Flag to enable byte-wise shuffle pre-compression filter

filter_id = 32001
filter_name = 'blosc'

Blosc2

class hdf5plugin.Blosc2(cname='blosclz', clevel=5, filters=1)

h5py.Group.create_dataset’s compression arguments for using blosc2 filter.

WARNING: This is a pre-release version of the HDF5 filter, only for testing purpose.

It can be passed as keyword arguments:

f = h5py.File('test.h5', 'w')
f.create_dataset(
    'blosc2_byte_shuffle_blosclz',
    data=numpy.arange(100),
    **hdf5plugin.Blosc2(cname='blosclz', clevel=9, shuffle=hdf5plugin.Blosc2.SHUFFLE))
f.close()
Parameters:
  • cname (str) – blosclz (default), lz4, lz4hc, zlib, zstd

  • clevel (int) – Compression level from 0 (no compression) to 9 (maximum compression). Default: 5.

  • filters (int) – One of: - Blosc2.NOFILTER (0): No pre-compression filter - Blosc2.SHUFFLE (1): Byte-wise shuffle (default) - Blosc2.BITSHUFFLE (2): Bit-wise shuffle - Blosc2.DELTA (3): Stores diff’ed blocks - Blosc3.TRUNC_PREC (4): Zeroes the least significant bits of the mantissa

BITSHUFFLE = 2

Flag to enable bit-wise shuffle pre-compression filter

DELTA = 3

Flag to store blocks inside a chunk diff’ed with respect to first block in the chunk

NOFILTER = 0

Flag to disable pre-compression filter

SHUFFLE = 1

Flag to enable byte-wise shuffle pre-compression filter

TRUNC_PREC = 4

Flag to zeroes the least significant bits of the mantissa of float32 and float64 types

filter_id = 32026
filter_name = 'blosc2'

BZip2

class hdf5plugin.BZip2(blocksize=9)

h5py.Group.create_dataset’s compression arguments for using BZip2 filter.

It can be passed as keyword arguments:

f = h5py.File('test.h5', 'w')
f.create_dataset(
    'bzip2',
    data=numpy.arange(100),
    **hdf5plugin.BZip2(blocksize=5))
f.close()
Parameters:

blocksize (int) – Size of the blocks as a multiple of 100k

filter_id = 307
filter_name = 'bzip2'

FciDecomp

class hdf5plugin.FciDecomp(*args, **kwargs)

h5py.Group.create_dataset’s compression arguments for using FciDecomp filter.

It can be passed as keyword arguments:

f = h5py.File('test.h5', 'w')
f.create_dataset(
    'fcidecomp',
    data=numpy.arange(100),
    **hdf5plugin.FciDecomp())
f.close()
filter_id = 32018
filter_name = 'fcidecomp'

LZ4

class hdf5plugin.LZ4(nbytes=0)

h5py.Group.create_dataset’s compression arguments for using lz4 filter.

It can be passed as keyword arguments:

f = h5py.File('test.h5', 'w')
f.create_dataset('lz4', data=numpy.arange(100),
    **hdf5plugin.LZ4(nbytes=0))
f.close()
Parameters:

nbytes (int) – The number of bytes per block. It needs to be in the range of 0 < nbytes < 2113929216 (1,9GB). Default: 0 (for 1GB per block).

filter_id = 32004
filter_name = 'lz4'

SZ

class hdf5plugin.SZ(absolute=None, relative=None, pointwise_relative=None)

h5py.Group.create_dataset’s compression arguments for using SZ filter.

It can be passed as keyword arguments:

f = h5py.File('test.h5', 'w')
f.create_dataset(
    'sz',
    data=numpy.random.random(100),
    **hdf5plugin.SZ())
f.close()

This filter provides different modes:

  • Absolute mode: To use, set the absolute argument. It ensures that the resulting values will be within the provided absolute tolerance.

    f.create_dataset(
        'sz_absolute',
        data=numpy.random.random(100),
        **hdf5plugin.SZ(absolute=0.1))
    
  • Relative mode: To use, set the relative argument. It ensures that the resulting values will be within the provided relative tolerance. The tolerance will be computed by multiplying the provided argument by the range of the data values.

    f.create_dataset(
        'sz_relative',
        data=numpy.random.random(100),
        **hdf5plugin.SZ(relative=0.01))
    
  • Point-wise relative mode: To use, set the pointwise_relative argument. It ensures that each grid point of the resulting values will be within the provided relative tolerance.

    f.create_dataset(
        'sz_pointwise_relative',
        data=numpy.random.random(100),
        **hdf5plugin.SZ(pointwise_relative=0.01))
    

For more details about the compressor SZ.

filter_id = 32017
filter_name = 'sz'

SZ3

class hdf5plugin.SZ3(absolute=None, relative=None, norm2=None, peak_signal_to_noise_ratio=None)

h5py.Group.create_dataset’s compression arguments for using SZ3 filter.

It can be passed as keyword arguments:

  • Absolute mode: To use, set the absolute argument. It ensures that the resulting values will be within the provided absolute tolerance.

    f.create_dataset(
        'sz3_absolute',
        data=numpy.random.random(100),
        **hdf5plugin.SZ3(absolute=0.1))
    

For more details about the compressor, see SZ3.

filter_id = 32024
filter_name = 'sz3'

Zfp

class hdf5plugin.Zfp(rate=None, precision=None, accuracy=None, reversible=False, minbits=None, maxbits=None, maxprec=None, minexp=None)

h5py.Group.create_dataset’s compression arguments for using ZFP filter.

It can be passed as keyword arguments:

f = h5py.File('test.h5', 'w')
f.create_dataset(
    'zfp',
    data=numpy.random.random(100),
    **hdf5plugin.Zfp())
f.close()

This filter provides different modes:

  • Fixed-rate mode: To use, set the rate argument. For details, see zfp fixed-rate mode.

    f.create_dataset(
        'zfp_fixed_rate',
        data=numpy.random.random(100),
        **hdf5plugin.Zfp(rate=10.0))
    
  • Fixed-precision mode: To use, set the precision argument. For details, see zfp fixed-precision mode.

    f.create_dataset(
        'zfp_fixed_precision',
        data=numpy.random.random(100),
        **hdf5plugin.Zfp(precision=10))
    
  • Fixed-accuracy mode: To use, set the accuracy argument For details, see zfp fixed-accuracy mode.

    f.create_dataset(
        'zfp_fixed_accuracy',
        data=numpy.random.random(100),
        **hdf5plugin.Zfp(accuracy=0.001))
    
  • Reversible (i.e., lossless) mode: To use, set the reversible argument to True For details, see zfp reversible mode.

    f.create_dataset(
        'zfp_reversible',
        data=numpy.random.random(100),
        **hdf5plugin.Zfp(reversible=True))
    
  • Expert mode: To use, set the minbits, maxbits, maxprec and minexp arguments. For details, see zfp expert mode.

    f.create_dataset(
        'zfp_expert',
        data=numpy.random.random(100),
        **hdf5plugin.Zfp(minbits=1, maxbits=16657, maxprec=64, minexp=-1074))
    
Parameters:
  • rate (float) – Use fixed-rate mode and set the number of compressed bits per value.

  • precision (float) – Use fixed-precision mode and set the number of uncompressed bits per value.

  • accuracy (float) – Use fixed-accuracy mode and set the absolute error tolerance.

  • reversible (bool) – If True, it uses the reversible (i.e., lossless) mode.

  • minbits (int) – Minimum number of compressed bits used to represent a block.

  • maxbits (int) – Maximum number of bits used to represent a block.

  • maxprec (int) – Maximum number of bit planes encoded. It controls the relative error.

  • minexp (int) – Smallest absolute bit plane number encoded. It controls the absolute error.

filter_id = 32013
filter_name = 'zfp'

Zstd

class hdf5plugin.Zstd(clevel=3)

h5py.Group.create_dataset’s compression arguments for using FciDecomp filter.

It can be passed as keyword arguments:

f = h5py.File('test.h5', 'w')
f.create_dataset(
    'zstd',
    data=numpy.arange(100),
    **hdf5plugin.Zstd())
f.close()
Parameters:

clevel (int) – Compression level from 1 (lowest compression) to 22 (maximum compression). Ultra compression extends from 20 through 22. Default: 3.

f = h5py.File('test.h5', 'w')
f.create_dataset(
    'zstd',
    data=numpy.arange(100),
    **hdf5plugin.Zstd(clevel=22))
f.close()
filter_id = 32015
filter_name = 'zstd'

Get information about hdf5plugin

Constants:

hdf5plugin.PLUGIN_PATH

Directory where the provided HDF5 filter plugins are stored.

Functions:

hdf5plugin.get_filters(filters=('bshuf', 'blosc', 'blosc2', 'bzip2', 'fcidecomp', 'lz4', 'sz', 'sz3', 'zfp', 'zstd'))

Returns selected filter classes.

By default it returns all filter classes.

Parameters:

filters (Union[str,int,Tuple[Union[str,int]]) – Filter name or ID or sequence of filter names or IDs (default: all filters). It also supports the value “registered” which selects currently available filters.

Returns:

Tuple of filter classes

hdf5plugin.get_config()

Provides information about build configuration and filters registered by hdf5plugin.

Manage registered filters

When imported, hdf5plugin initialises and registers the filters it embeds if there is no already registered filters for the corresponding filter IDs.

h5py gives access to HDF5 functions handling registered filters in h5py.h5z. This module allows checking the filter availability and registering/unregistering filters.

hdf5plugin provides an extra register function to register the filters it provides, e.g., to override an already loaded filters. Registering with this function is required to perform additional initialisation and enable writing compressed data with the given filter.

hdf5plugin.register(filters=('bshuf', 'blosc', 'blosc2', 'bzip2', 'fcidecomp', 'lz4', 'sz', 'sz3', 'zfp', 'zstd'), force=True)

Initialise and register hdf5plugin embedded filters given their names or IDs.

Parameters:
  • filters (Union[str,int,Tuple[Union[str,int]]) – Filter name or ID or sequence of filter names or IDs.

  • force (bool) – True to register the filter even if a corresponding one if already available. False to skip already available filters.

Returns:

True if all filters were registered successfully, False otherwise.

Return type:

bool

Use HDF5 filters in other applications

Non h5py or non-Python users can also benefit from the supplied HDF5 compression filters for reading compressed datasets by setting the HDF5_PLUGIN_PATH environment variable the value of hdf5plugin.PLUGIN_PATH, which can be retrieved from the command line with:

python -c "import hdf5plugin; print(hdf5plugin.PLUGIN_PATH)"

For instance:

export HDF5_PLUGIN_PATH=$(python -c "import hdf5plugin; print(hdf5plugin.PLUGIN_PATH)")

should allow MatLab or IDL users to read data compressed using the supported plugins.

Setting the HDF5_PLUGIN_PATH environment variable allows already existing programs or Python code to read compressed data without any modification.