SimpleJSON and NumPy array

Question

What is the most efficient way of serializing a numpy array using simplejson?

Answer 1

You can also answer this with just a function passed into json.dumps in this way:

json.dumps(np.array([1, 2, 3]), default=json_numpy_serializer)

With

import numpy as np

def json_numpy_serialzer(o):
    """ Serialize numpy types for json

    Parameters:
        o (object): any python object which fails to be serialized by json

    Example:

        >>> import json
        >>> a = np.array([1, 2, 3])
        >>> json.dumps(a, default=json_numpy_serializer)

    """
    numpy_types = (
        np.bool_,
        # np.bytes_, -- python `bytes` class is not json serializable     
        # np.complex64,  -- python `complex` class is not json serializable  
        # np.complex128,  -- python `complex` class is not json serializable
        # np.complex256,  -- special handling below
        # np.datetime64,  -- python `datetime.datetime` class is not json serializable
        np.float16,
        np.float32,
        np.float64,
        # np.float128,  -- special handling below
        np.int8,
        np.int16,
        np.int32,
        np.int64,
        # np.object_  -- should already be evaluated as python native
        np.str_,
        np.timedelta64,
        np.uint8,
        np.uint16,
        np.uint32,
        np.uint64,
        np.void,
    )

    if isinstance(o, np.ndarray):
        return o.tolist()
    elif isinstance(o, numpy_types):        
        return o.item()
    elif isinstance(o, np.float128):
        return o.astype(np.float64).item()
    # elif isinstance(o, np.complex256): -- no python native for np.complex256
    #     return o.astype(np.complex128).item() -- python `complex` class is not json serializable 
    else:
        raise TypeError("{} of type {} is not JSON serializable".format(repr(o), type(o)))

validated:

need_addition_json_handeling = (
    np.bytes_,
    np.complex64,  
    np.complex128, 
    np.complex256, 
    np.datetime64,
    np.float128,
)


numpy_types = tuple(set(np.typeDict.values()))

for numpy_type in numpy_types:
    print(numpy_type)

    if numpy_type == np.void:
        # complex dtypes evaluate as np.void, e.g.
        numpy_type = np.dtype([('name', np.str_, 16), ('grades', np.float64, (2,))])
    elif numpy_type in need_addition_json_handeling:
        print('python native can not be json serialized')
        continue

    a = np.ones(1, dtype=nptype)
    json.dumps(a, default=json_numpy_serialzer)