JSON Decimal encoder

import json
from decimal import Decimal

class DecimalEncoder(json.JSONEncoder):
    def default(self, obj):
        if isinstance(obj, Decimal):
            return float(obj)
        return json.JSONEncoder.default(self, obj)

# Output has one decimal, change format if you need more
json.encoder.FLOAT_REPR = lambda o: format(o, '.1f')

# Usage:
d = Decimal("42.5")
json.dumps(d, cls=DecimalEncoder)