Library Reference

First level variables

__version__

The version of the blosc package.

blosclib_version

The version of the Blosc C library.

clib_versions

A map for the versions of the compression libraries included in C library.

cnames

The list of compressors included in C library.

cname2clib

A map between compressor names and its libraries (or formats).

ncores

The number of cores detected.

Public functions

blosc.compress(bytesobj[, typesize=8, clevel=9, shuffle=blosc.SHUFFLE, cname='blosclz']])

Compress bytesobj, with a given type size.

Parameters:

bytesobj : bytes-like object (supporting the buffer interface)

The data to be compressed.

typesize : int

The data type size.

clevel : int (optional)

The compression level from 0 (no compression) to 9 (maximum compression). The default is 9.

shuffle : int (optional)

The shuffle filter to be activated. Allowed values are blosc.NOSHUFFLE, blosc.SHUFFLE and blosc.BITSHUFFLE. The default is blosc.SHUFFLE.

cname : string (optional)

The name of the compressor used internally in Blosc. It can be any of the supported by Blosc (‘blosclz’, ‘lz4’, ‘lz4hc’, ‘snappy’, ‘zlib’, ‘zstd’ and maybe others too). The default is ‘blosclz’.

Returns:

out : str / bytes

The compressed data in form of a Python str / bytes object.

Raises:

TypeError

If bytesobj doesn’t support the buffer interface.

ValueError

If bytesobj is too long. If typesize is not within the allowed range. If clevel is not within the allowed range. If cname is not a valid codec.

Examples

>>> import array
>>> a = array.array('i', range(1000*1000))
>>> a_bytesobj = a.tostring()
>>> c_bytesobj = blosc.compress(a_bytesobj, typesize=4)
>>> len(c_bytesobj) < len(a_bytesobj)
True
blosc.compress_ptr(address, items[, typesize=8, clevel=9, shuffle=blosc.SHUFFLE, cname='blosclz']])

Compress the data at address with given items and typesize.

Parameters:

address : int or long

the pointer to the data to be compressed

items : int

The number of items (of typesize) to be compressed.

typesize : int

The data type size.

clevel : int (optional)

The compression level from 0 (no compression) to 9 (maximum compression). The default is 9.

shuffle : int (optional)

The shuffle filter to be activated. Allowed values are blosc.NOSHUFFLE, blosc.SHUFFLE and blosc.BITSHUFFLE. The default is blosc.SHUFFLE.

cname : string (optional)

The name of the compressor used internally in Blosc. It can be any of the supported by Blosc (‘blosclz’, ‘lz4’, ‘lz4hc’, ‘snappy’, ‘zlib’, ‘zstd’ and maybe others too). The default is ‘blosclz’.

Returns:

out : str / bytes

The compressed data in form of a Python str / bytes object.

Raises:

TypeError

If address is not of type int or long.

ValueError

If items * typesize is larger than the maximum allowed buffer size. If typesize is not within the allowed range. If clevel is not within the allowed range. If cname is not within the supported compressors.

Notes

This function can be used anywhere that a memory address is available in Python. For example the Numpy “__array_interface__[‘data’][0]” construct, or when using the ctypes modules.

Importantly, the user is responsible for making sure that the memory address is valid and that the memory pointed to is contiguous. Passing a non-valid address has a high likelihood of crashing the interpreter by segfault.

Examples

>>> import numpy
>>> items = 7
>>> np_array = numpy.arange(items)
>>> c = blosc.compress_ptr(np_array.__array_interface__['data'][0],         items, np_array.dtype.itemsize)
>>> d = blosc.decompress(c)
>>> np_ans = numpy.fromstring(d, dtype=np_array.dtype)
>>> (np_array == np_ans).all()
True
>>> import ctypes
>>> typesize = 8
>>> data = [float(i) for i in range(items)]
>>> Array = ctypes.c_double * items
>>> a = Array(*data)
>>> c = blosc.compress_ptr(ctypes.addressof(a), items, typesize)
>>> d = blosc.decompress(c)
>>> import struct
>>> ans = [struct.unpack('d', d[i:i+typesize])[0]             for i in range(0, items*typesize, typesize)]
>>> data == ans
True
blosc.decompress(bytesobj)

Decompresses a bytesobj compressed object.

Parameters:

bytesobj : str / bytes

The data to be decompressed.

as_bytearray : bool, optional

If this flag is True then the return type will be a bytearray object instead of a bytesobject.

Returns:

out : str / bytes or bytearray

The decompressed data in form of a Python str / bytes object. If as_bytearray is True then this will be a bytearray object, otherwise this will be a str/ bytes object.

Raises:

TypeError

If bytesobj is not of type bytes or string.

Examples

>>> import array
>>> a = array.array('i', range(1000*1000))
>>> a_bytesobj = a.tostring()
>>> c_bytesobj = blosc.compress(a_bytesobj, typesize=4)
>>> a_bytesobj2 = blosc.decompress(c_bytesobj)
>>> a_bytesobj == a_bytesobj2
True
>>> b"" == blosc.decompress(blosc.compress(b"", 1))
True
>>> b"1"*7 == blosc.decompress(blosc.compress(b"1"*7, 8))
True
>>> type(blosc.decompress(blosc.compress(b"1"*7, 8),
...                                      as_bytearray=True)) is bytearray
True
blosc.decompress_ptr(bytesobj, address)

Decompresses a bytesobj compressed object into the memory at address.

Parameters:

bytesobj : str / bytes

The data to be decompressed.

address : int or long

the pointer to the data to be compressed

Returns:

nbytes : int

the number of bytes written to the buffer

Raises:

TypeError

If bytesobj is not of type bytes or string. If address is not of type int or long.

Notes

This function can be used anywhere that a memory address is available in Python. For example the Numpy “__array_interface__[‘data’][0]” construct, or when using the ctypes modules.

Importantly, the user is responsible for making sure that the memory address is valid and that the memory pointed to is contiguous and can be written to. Passing a non-valid address has a high likelihood of crashing the interpreter by segfault.

Examples

>>> import numpy
>>> items = 7
>>> np_array = numpy.arange(items)
>>> c = blosc.compress_ptr(np_array.__array_interface__['data'][0],         items, np_array.dtype.itemsize)
>>> np_ans = numpy.empty(items, dtype=np_array.dtype)
>>> nbytes = blosc.decompress_ptr(c, np_ans.__array_interface__['data'][0])
>>> (np_array == np_ans).all()
True
>>> nbytes == items * np_array.dtype.itemsize
True
>>> import ctypes
>>> typesize = 8
>>> data = [float(i) for i in range(items)]
>>> Array = ctypes.c_double * items
>>> in_array = Array(*data)
>>> c = blosc.compress_ptr(ctypes.addressof(in_array), items, typesize)
>>> out_array = ctypes.create_string_buffer(items*typesize)
>>> nbytes = blosc.decompress_ptr(c, ctypes.addressof(out_array))
>>> import struct
>>> ans = [struct.unpack('d', out_array[i:i+typesize])[0]             for i in range(0, items*typesize, typesize)]
>>> data == ans
True
>>> nbytes == items * typesize
True
blosc.pack_array(array[, clevel=9, shuffle=blosc.SHUFFLE, cname='blosclz']])

Pack (compress) a NumPy array.

Parameters:

array : ndarray

The NumPy array to be packed.

clevel : int (optional)

The compression level from 0 (no compression) to 9 (maximum compression). The default is 9.

shuffle : int (optional)

The shuffle filter to be activated. Allowed values are blosc.NOSHUFFLE, blosc.SHUFFLE and blosc.BITSHUFFLE. The default is blosc.SHUFFLE.

cname : string (optional)

The name of the compressor used internally in Blosc. It can be any of the supported by Blosc (‘blosclz’, ‘lz4’, ‘lz4hc’, ‘snappy’, ‘zlib’, ‘zstd’ and maybe others too). The default is ‘blosclz’.

Returns:

out : str / bytes

The packed array in form of a Python str / bytes object.

Raises:

TypeError

If array does not quack like a numpy ndarray.

ValueError

If array.itemsize * array.size is larger than the maximum allowed

buffer size.

If typesize is not within the allowed range. If clevel is not within the allowed range. If cname is not within the supported compressors.

Examples

>>> import numpy
>>> a = numpy.arange(1e6)
>>> parray = blosc.pack_array(a)
>>> len(parray) < a.size*a.itemsize
True
blosc.unpack_array(packed_array)

Unpack (decompress) a packed NumPy array.

Parameters:

packed_array : str / bytes

The packed array to be decompressed.

Returns:

out : ndarray

The decompressed data in form of a NumPy array.

Raises:

TypeError

If packed_array is not of type bytes or string.

Examples

>>> import numpy
>>> a = numpy.arange(1e6)
>>> parray = blosc.pack_array(a)
>>> len(parray) < a.size*a.itemsize
True
>>> a2 = blosc.unpack_array(parray)
>>> numpy.alltrue(a == a2)
True

Utilities

blosc.clib_info(cname)

Return info for compression libraries in C library.

Parameters:

cname : str

The compressor name.

Returns:

out : tuple

The associated library name and version.

blosc.compressor_list()

Returns a list of compressors available in C library.

Parameters:

None

Returns:

out : list

The list of names.

blosc.detect_number_of_cores()

Detect the number of cores in this system.

Returns:

out : int

The number of cores in this system.

blosc.free_resources()

Free possible memory temporaries and thread resources.

Returns:out : None

Notes

Blosc maintain a pool of threads waiting for work as well as some temporary space. You can use this function to release these resources when you are not going to use Blosc for a long while.

Examples

>>> blosc.free_resources()
>>>
blosc.get_clib(bytesobj)

Return the name of the compression library for Blosc bytesobj buffer.

Parameters:

bytesobj : str / bytes

The compressed buffer.

Returns:

out : str

The name of the compression library.

blosc.set_blocksize(blocksize)

Force the use of a specific blocksize. If 0, an automatic blocksize will be used (the default).

Notes

This is a low-level function and is recommened for expert users only.

Examples

>>> blosc.set_blocksize(512)
blosc.set_nthreads(nthreads)

Set the number of threads to be used during Blosc operation.

Parameters:

nthreads : int

The number of threads to be used during Blosc operation.

Returns:

out : int

The previous number of used threads.

Raises:

ValueError

If nthreads is larger that the maximum number of threads blosc can use.

Notes

The number of threads for Blosc is the maximum number of cores detected on your machine (via detect_number_of_cores). In some cases Blosc gets better results if you set the number of threads to a value slightly below than your number of cores.

Examples

Set the number of threads to 2 and then to 1:

>>> oldn = blosc.set_nthreads(2)
>>> blosc.set_nthreads(1)
2
blosc.set_releasegil(gitstate)

Sets a boolean on whether to release the Python global inter-lock (GIL) during c-blosc compress and decompress operations or not. This defaults to False.

Notes

Designed to be used with larger chunk sizes and a ThreadPool. There is a small performance penalty with releasing the GIL that will more harshly penalize small block sizes.

Examples

>>> oldReleaseState = blosc.set_releasegil(True)
blosc.print_versions()

Print all the versions of software that python-blosc relies on.