SChunk.__init__#

SChunk.__init__(chunksize: int | None = None, data: object = None, **kwargs: dict | CParams | Storage | DParams) → None#

Create a new super-chunk, or open an existing one.

Parameters:

  • chunksize (int, optional) – The size, in bytes, of the chunks in the super-chunk. If not provided, it is set automatically to a reasonable value.

  • data (bytes-like object, optional) – The data to be split into different chunks of size chunksize. If None, the Schunk instance will be empty initially.

  • kwargs (dict, optional) –

    Storage parameters. The default values are in blosc2.Storage. Supported keyword arguments:

    storage: blosc2.Storage or dict

    All the storage parameters that you want to use as a blosc2.Storage or dict instance.

    cparams: blosc2.CParams or dict

    All the compression parameters that you want to use as a blosc2.CParams or dict instance.

    dparams: blosc2.DParams or dict

    All the decompression parameters that you want to use as a blosc2.DParams or dict instance.

    others: Any

    If storage is not passed, all the parameters of a blosc2.Storage can be passed as keyword arguments.

Examples

>>> import blosc2
>>> import numpy as np
>>> import os.path
>>> import shutil
>>> import tempfile
>>> cparams = blosc2.CParams()
>>> dparams = blosc2.DParams()
>>> storage = blosc2.Storage(contiguous=True)
>>> schunk = blosc2.SChunk(cparams=cparams, dparams=dparams, storage=storage)

In the following, we will write and read a super-chunk to and from disk via memory-mapped files.

>>> a = np.arange(3, dtype=np.int64)
>>> chunksize = a.size * a.itemsize
>>> n_chunks = 2
>>> tmpdirname = tempfile.mkdtemp()
>>> urlpath = os.path.join(tmpdirname, 'schunk.b2frame')

Optional: we intend to write 2 chunks of 24 bytes each, and we expect the compressed size to be smaller than the original size. Therefore, we generously set the initial size of the mapping to 48 bytes effectively avoiding remappings.

>>> initial_mapping_size = chunksize * n_chunks
>>> schunk_mmap = blosc2.SChunk(
...     chunksize=chunksize,
...     mmap_mode="w+",
...     initial_mapping_size=initial_mapping_size,
...     urlpath=urlpath,
... )
>>> schunk_mmap.append_data(a)
1
>>> schunk_mmap.append_data(a * 2)
2

Optional: explicitly close the file and free the mapping.

>>> del schunk_mmap

Reading the data back again via memory-mapped files:

>>> schunk_mmap = blosc2.open(urlpath, mmap_mode="r")
>>> np.frombuffer(schunk_mmap.decompress_chunk(0), dtype=np.int64).tolist()
[0, 1, 2]
>>> np.frombuffer(schunk_mmap.decompress_chunk(1), dtype=np.int64).tolist()
[0, 2, 4]
>>> shutil.rmtree(tmpdirname)
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