Python to JSON Serialization fails on Decimal [duplicate]

Answer 1

I can't believe that no one here talked about using simplejson, which supports deserialization of Decimal out of the box.

import simplejson
from decimal import Decimal

simplejson.dumps({"salary": Decimal("5000000.00")})
'{"salary": 5000000.00}'

simplejson.dumps({"salary": Decimal("1.1")+Decimal("2.2")-Decimal("3.3")})
'{"salary": 0.0}'

Answer 2

It is not (no longer) recommended you create a subclass; the json.dump() and json.dumps() functions take a default function:

def decimal_default(obj):
    if isinstance(obj, decimal.Decimal):
        return float(obj)
    raise TypeError

json.dumps({'x': decimal.Decimal('5.5')}, default=decimal_default)

Demo:

>>> def decimal_default(obj):
...     if isinstance(obj, decimal.Decimal):
...         return float(obj)
...     raise TypeError
... 
>>> json.dumps({'x': decimal.Decimal('5.5')}, default=decimal_default)
'{"x": 5.5}'

The code you found only worked on Python 2.6 and overrides a private method that is no longer called in later versions.

Answer 3

If you're using Django. There is a great class for Decimal and date fields:

https://docs.djangoproject.com/en/1.10/topics/serialization/#djangojsonencoder

To use it:

import json
from django.core.serializers.json import DjangoJSONEncoder

json.dumps(value, cls=DjangoJSONEncoder)