ZnJSON

Package to Encode/Decode some common file formats to json

Available via pip install znjson

In comparison to pickle this allows having readable json files combined with some serialized data.

Example

import numpy as np
import json
import znjson

data = json.dumps(
    obj={"data_np": np.arange(2), "data": [x for x in range(10)]},
    cls=znjson.ZnEncoder,
    indent=4
)
_ = json.loads(data, cls=znjson.ZnDecoder)

The resulting *.json file is partially readable and looks like this:

{
    "data_np": {
        "_type": "np.ndarray_small",
        "value": [
            0,
            1
        ]
    },
    "data": [
        0,
        1,
        2,
        3,
        4
    ]
}

Custom Converter

ZnJSON allows you to easily add custom converters. Let's write a serializer for datetime.datetime.

from znjson import ConverterBase
from datetime import datetime

class DatetimeConverter(ConverterBase):
    """Encode/Decode datetime objects

    Attributes
    ----------
    level: int
        Priority of this converter over others.
        A higher level will be used first, if there
        are multiple converters available
    representation: str
        An unique identifier for this converter.
    instance:
        Used to select the correct converter.
        This should fulfill isinstance(other, self.instance)
        or __eq__ should be overwritten.
    """
    level = 100
    representation = "datetime"
    instance = datetime

    def encode(self, obj: datetime) -> str:
        """Convert the datetime object to str / isoformat"""
        return obj.isoformat()
    def decode(self, value: str) -> datetime:
        """Create datetime object from str / isoformat"""
        return datetime.fromisoformat(value)

This allows us to use this new serializer:

znjson.config.register(DatetimeConverter) # we need to register the new converter first
json_string = json.dumps(dt, cls=znjson.ZnEncoder, indent=4)
json.loads(json_string, cls=znjson.ZnDecoder)

and will result in

{
    "_type": "datetime",
    "value": "2022-03-11T09:47:35.280331"
}

If you don't want to register your converter to be used everywhere, simply use:

json_string = json.dumps(dt, cls=znjson.ZnEncoder.from_converters(DatetimeConverter))