cannot pickle Decimal

[JssDWt]

jsonpickle serializes Decimal as null.

Steps to reproduce:

• install jsonpickle 1.0 and simplejson 3.16.0 in a python 3.7 environment
• execute the following code:

import jsonpickle
from decimal import Decimal
jsonpickle.set_preferred_backend('simplejson')
jsonpickle.set_encoder_options('simplejson', use_decimal=True)
print(jsonpickle.encode(Decimal('2.0'), unpicklable=False, warn=True))

This prints:

UserWarning: jsonpickle cannot pickle Decimal('2.0'): replaced with None
warnings.warn(msg)
null

[rafalkasa]

Please try https://stackoverflow.com/questions/54276418/jsonpickle-with-simplejson-backend-serializes-decimal-as-null

import jsonpickle
from decimal import Decimal

jsonpickle.set_preferred_backend('simplejson')
jsonpickle.set_encoder_options('simplejson', use_decimal=True)

class DecimalHandler(jsonpickle.handlers.BaseHandler):

    def flatten(self, obj, data):

        return obj.__str__() #Convert to json friendly format

jsonpickle.handlers.registry.register(Decimal, DecimalHandler)

class MyClass():
    def __init__(self, amount):
        self.amount = amount

    def to_json(self):
        return jsonpickle.dumps(self, unpicklable=False)

if __name__ == '__main__':
    obj = MyClass(Decimal('1.0'))
    print(obj.to_json())

[JssDWt]

This actually prints {"amount": "1.0"}, which is not what I want. I'd expect {"amount": 1.0}.
PS I'm the one who asked that question on SO.

[woutdenolf]

Why do you expect a float? If you are worried about rounding errors, shouldn't you expect a str? Converting to float defies the purpose of having Decimal in the first place:

from decimal import Decimal
string = '1.00000000000000000000000001'
decimal = Decimal(string)
assert str(decimal) == string  # OK
assert str(float(decimal)) == string  # NOK
assert float(decimal) == decimal  # NOK

[JssDWt]

I do not expect a float. I expect to create a json value as a number, not a string. json does not interpret the kind of number or the precision. Serializing as a string would cause hassle explaining to other clients they should interpret the string as a number, which is not what I want.
Simplejson is capable of doing what I want and serializes Decimal as a json number if use_decimal is True. I'd expect the same to happen when using jsonpickle with simplejson as a backend.
The example you provide is python specific, and does not have to do much with json numbers.

[davvid]

I provided an example in the stackoverflow thread demonstrating how to do this. Additionally, I added a new use_decimal mode to encode/dumps that avoids converting to null and allows simplejson to handle the value rather than getting handled by jsonpickle.

https://jsonpickle.readthedocs.io/en/latest/api.html#jsonpickle.pickler.encode

It sounds like your use case is pretty specific, so please see the S.O. thread for more details.

[JssDWt]

@davvid that is excellent. Thank you very much.