Question

I’m pulling a sum from a DB which is a decimal value.
I’m trying to use that value in a JSON result

json.dumps( { 'sum': amount } ) #where amount is my Decimal

Django can’t serialize the Decimal.
I can convert it to a string, but I’d like a numeric type within the JSON.
If I try and convert it to a float I end up with more than 2 decimal places.

What needs to happen, if possible, to get a result like the following?

{ 'sum': 500.50 }

Answer 1

What you can do is extend the JSONDecoder class to provide a custom serializer for the Decimal type, similar to the example in this document: http://docs.python.org/py3k/library/json.html

>>> import json
>>> class DecimalEncoder(json.JSONEncoder):
...     def default(self, obj):
...         if isinstance(obj, Decimal):
...             return "%.2f" % obj
...         return json.JSONEncoder.default(self, obj)
...

That’s a nonworking example of how to do it, hopefully a good starting point for you.