Python 3.x cannot serialize Decimal() to JSON
I wanted to serialize Decimal to JSON, and also deserialize it back to actual Decimal class objects in a dictionary elsewhere.
Here is my sample program which works for me (Python 3.6):
import json
from decimal import Decimal
import decimal
class DecimalEncoder(json.JSONEncoder):
def default(self, obj):
if isinstance(obj, decimal.Decimal):
return {'__Decimal__': str(obj)}
# Let the base class default method raise the TypeError
return json.JSONEncoder.default(self, obj)
def as_Decimal(dct):
if '__Decimal__' in dct:
return decimal.Decimal(dct['__Decimal__'])
return dct
sample_dict = {
"sample1": Decimal("100"),
"sample2": [ Decimal("2.0"), Decimal("2.1") ],
"sample3": Decimal("3.1415"),
"other": "hello!"
}
print("1. sample_dict is:\n{0}\n".format(sample_dict))
sample_dict_encoded_as_json_string = json.dumps(sample_dict, cls=DecimalEncoder)
print("2. sample_dict_encoded_as_json_string is:\n{0}\n".format(sample_dict_encoded_as_json_string))
sample_dict_recreated = json.loads(sample_dict_encoded_as_json_string, object_hook=as_Decimal)
print("3. sample_dict_recreated is:\n{0}\n".format(sample_dict_recreated))
And here is the output:
1. sample_dict is:
{'sample1': Decimal('100'), 'sample2': [Decimal('2.0'), Decimal('2.1')], 'sample3': Decimal('3.1415'), 'other': 'hello!'}
2. sample_dict_encoded_as_json_string is:
{"sample1": {"__Decimal__": "100"}, "sample2": [{"__Decimal__": "2.0"}, {"__Decimal__": "2.1"}], "sample3": {"__Decimal__": "3.1415"}, "other": "hello!"}
3. sample_dict_recreated is:
{'sample1': Decimal('100'), 'sample2': [Decimal('2.0'), Decimal('2.1')], 'sample3': Decimal('3.1415'), 'other': 'hello!'}
Hope this helps!
That answer turned out to be outdated and there was another answer with the working solution:
class DecimalEncoder(json.JSONEncoder):
def default(self, o):
if isinstance(o, decimal.Decimal):
return str(o)
return super(DecimalEncoder, self).default(o)
Note that this will convert the decimal to its string representation (e.g.; "1.2300"
) to a. not lose significant digits and b. prevent rounding errors.