Decimal numbers in python json dump

txjson.py

# In response to https://bitcointalk.org/index.php?topic=56424.msg1454348#msg1454348

# Highlights that json encoding of floats is no good
# and that decimals can be used for encoding.

import json
from decimal import Decimal as D

d1 = D(11) / D(10) # 1.1
d2 = D(22) / D(10) # 2.2
f1 = 1.1
f2 = 2.2

# See http://docs.python.org/2/library/json.html
# Extending JSONEncoder:
class DecimalEncoder(json.JSONEncoder):
    def default(self, obj):
        if isinstance(obj, D):
            return float(obj)
        return json.JSONEncoder.default(self, obj)

print json.dumps({'a': f1+f2})
# {"a": 3.3000000000000003} # This is not what we want, should be 3.3 exactly

#print json.dumps({'a': d1+d2})
# Fails for json encoding of decimal

print DecimalEncoder().encode({'a': d1+d2})
# {"a": 3.3}

Thank you!