ndarray_to_json.py

# This file is part of the micropython-ulab project, https://github.com/v923z/micropython-ulab
#
# The MIT License (MIT)
#
# Copyright (c) 2022 Zoltán Vörös

import sys

use_ulab = False

try:
    from ubinascii import b2a_base64 as b64encode
    from ubinascii import hexlify
    import ujson as json
    from ulab import numpy as np
    use_ulab = True
except:
    from base64 import b64encode
    import json
    import numpy as np
    from numpy.lib.format import dtype_to_descr

def ulab_dtype_to_descr(dtype):
    desc = '>'
    if sys.byteorder == 'little':
        desc = '<'

    if dtype == ord('B'):
        desc = '|u1'
    elif dtype == ord('b'):
        desc = '|i1'
    elif dtype == ord('H'):
        desc = desc + 'u2'
    elif dtype == ord('h'):
        desc = desc + 'i2'
    elif dtype == ord('d'):
        desc = desc + 'f8'
    elif dtype == ord('f'):
        desc = desc + 'f4'
    elif dtype == ord('c'):
        desc = desc + 'c16'
        if np.array([1], dtype=np.float).itemsize == 4:
            desc = desc + 'c8'

    return desc

def ndarray_to_json(obj, b64=True):
    """
    Turn an ndarray into a json string, using either base64 encoding or hexify
    Returns a serialised dictionary with three keys:

    - dtype: a valid numpy dtype string (one of |u1, |i1, <u2, <i2, <f4, <f8, <c8, <c16, >u2, >i2, >f4, >f8, >c8, >c16)
    - array: the hexified, or base64-encoded raw data array
    - shape: the shape of the array (a list or tuple of integers)

    Usage:
        ndarray = np.array([1, 2, 3], dtype=np.uint8)
        ndarray_to_json(ndarray, b64=True)
    """

    if not isinstance(obj, np.ndarray):
         raise TypeError('input argument must be an ndarray')

    if use_ulab:
        dtype_desciptor = ulab_dtype_to_descr(obj.dtype)
    else:
        dtype_desciptor = dtype_to_descr(obj.dtype)

    if not b64:
        data = hexlify(obj.tobytes())
    else:
        data = b64encode(obj.tobytes())

    return json.dumps({'array': data, 'dtype': dtype_desciptor, 'shape': obj.shape})