blosc2.schunk.SChunk.prefilter#

SChunk.prefilter(input_dtype: dtype, output_dtype: dtype = None) → None#

Decorator to set a function as a prefilter.

This function will be executed each time before compressing the data. It will receive three parameters:

  • The actual data as a ndarray from which to read,

  • The ndarray to be filled,

  • The offset inside the SChunk instance where the corresponding block begins (see example below).

Parameters:

  • input_dtype (np.dtype) – Data type of the input that will be processed the prefilter function.

  • output_dtype (np.dtype, optional) – Data type of the output that will be filled by the prefilter function. If None (default), it will be the same as input_dtype.

Returns:

out

Return type:

None

Notes

See also

remove_prefilter(), postfilter(), filler()

Examples

# Set the compression and decompression parameters
input_dtype = np.dtype(np.int32)
output_dtype = np.dtype(np.float32)
cparams = blosc2.CParams(typesize=output_dtype.itemsize, nthreads=1)
# Create schunk
schunk = blosc2.SChunk(chunksize=200 * 1000 * input_dtype.itemsize, cparams=cparams)

# Set prefilter with decorator
@schunk.prefilter(input_dtype, output_dtype)
def prefilter(input, output, offset):
    output[:] = input - np.pi
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