I have a Decimal(\'3.9\')
as part of an object, and wish to encode this to a JSON string which should look like {\'x\': 3.9}
. I don\'t care about p
This is what I have, extracted from our class
class CommonJSONEncoder(json.JSONEncoder):
"""
Common JSON Encoder
json.dumps(myString, cls=CommonJSONEncoder)
"""
def default(self, obj):
if isinstance(obj, decimal.Decimal):
return {'type{decimal}': str(obj)}
class CommonJSONDecoder(json.JSONDecoder):
"""
Common JSON Encoder
json.loads(myString, cls=CommonJSONEncoder)
"""
@classmethod
def object_hook(cls, obj):
for key in obj:
if isinstance(key, six.string_types):
if 'type{decimal}' == key:
try:
return decimal.Decimal(obj[key])
except:
pass
def __init__(self, **kwargs):
kwargs['object_hook'] = self.object_hook
super(CommonJSONDecoder, self).__init__(**kwargs)
Which passes unittest:
def test_encode_and_decode_decimal(self):
obj = Decimal('1.11')
result = json.dumps(obj, cls=CommonJSONEncoder)
self.assertTrue('type{decimal}' in result)
new_obj = json.loads(result, cls=CommonJSONDecoder)
self.assertEqual(new_obj, obj)
obj = {'test': Decimal('1.11')}
result = json.dumps(obj, cls=CommonJSONEncoder)
self.assertTrue('type{decimal}' in result)
new_obj = json.loads(result, cls=CommonJSONDecoder)
self.assertEqual(new_obj, obj)
obj = {'test': {'abc': Decimal('1.11')}}
result = json.dumps(obj, cls=CommonJSONEncoder)
self.assertTrue('type{decimal}' in result)
new_obj = json.loads(result, cls=CommonJSONDecoder)
self.assertEqual(new_obj, obj)
I tried switching from simplejson to builtin json for GAE 2.7, and had issues with the decimal. If default returned str(o) there were quotes (because _iterencode calls _iterencode on the results of default), and float(o) would remove trailing 0.
If default returns an object of a class that inherits from float (or anything that calls repr without additional formatting) and has a custom __repr__ method, it seems to work like I want it to.
import json
from decimal import Decimal
class fakefloat(float):
def __init__(self, value):
self._value = value
def __repr__(self):
return str(self._value)
def defaultencode(o):
if isinstance(o, Decimal):
# Subclass float with custom repr?
return fakefloat(o)
raise TypeError(repr(o) + " is not JSON serializable")
json.dumps([10.20, "10.20", Decimal('10.20')], default=defaultencode)
'[10.2, "10.20", 10.20]'
For Django users:
Recently came across TypeError: Decimal('2337.00') is not JSON serializable
while JSON encoding i.e. json.dumps(data)
Solution:
# converts Decimal, Datetime, UUIDs to str for Encoding
from django.core.serializers.json import DjangoJSONEncoder
json.dumps(response.data, cls=DjangoJSONEncoder)
But, now the Decimal value will be a string, now we can explicitly set the decimal/float value parser when decoding data, using parse_float
option in json.loads
:
import decimal
data = json.loads(data, parse_float=decimal.Decimal) # default is float(num_str)
You can create a custom JSON encoder as per your requirement.
import json
from datetime import datetime, date
from time import time, struct_time, mktime
import decimal
class CustomJSONEncoder(json.JSONEncoder):
def default(self, o):
if isinstance(o, datetime):
return str(o)
if isinstance(o, date):
return str(o)
if isinstance(o, decimal.Decimal):
return float(o)
if isinstance(o, struct_time):
return datetime.fromtimestamp(mktime(o))
# Any other serializer if needed
return super(CustomJSONEncoder, self).default(o)
The Decoder can be called like this,
import json
from decimal import Decimal
json.dumps({'x': Decimal('3.9')}, cls=CustomJSONEncoder)
and the output will be:
>>'{"x": 3.9}'
For anybody that wants a quick solution here is how I removed Decimal from my queries in Django
total_development_cost_var = process_assumption_objects.values('total_development_cost').aggregate(sum_dev = Sum('total_development_cost', output_field=FloatField()))
total_development_cost_var = list(total_development_cost_var.values())
Hope it helps
Simplejson 2.1 and higher has native support for Decimal type:
>>> json.dumps(Decimal('3.9'), use_decimal=True)
'3.9'
Note that use_decimal
is True
by default:
def dumps(obj, skipkeys=False, ensure_ascii=True, check_circular=True,
allow_nan=True, cls=None, indent=None, separators=None,
encoding='utf-8', default=None, use_decimal=True,
namedtuple_as_object=True, tuple_as_array=True,
bigint_as_string=False, sort_keys=False, item_sort_key=None,
for_json=False, ignore_nan=False, **kw):
So:
>>> json.dumps(Decimal('3.9'))
'3.9'
Hopefully, this feature will be included in standard library.