["python","json","formatting","floating-point"]
Format floats with standard json module

I am using the standard json module in python 2.6 to serialize a list of floats. However, I'm getting results like this: >>> import json >>> json.dumps([23.67, 23.97, 23.87]) '[23.670000000000002, 23.969999999999999, 23.870000000000001]' I want the floats to be formated with only two decimal digits. The output should look like this: >>> json.dumps([23.67, 23.97, 23.87]) '[23.67, 23.97, 23.87]' I have tried defining my own JSON Encoder class: class MyEncoder(json.JSONEncoder): def encode(self, obj): if isinstance(obj, float): return format(obj, '.2f') return json.JSONEncoder.encode(self, obj) This works for a sole float object: >>> json.dumps(23.67, cls=MyEncoder) '23.67' But fails for nested objects: >>> json.dumps([23.67, 23.97, 23.87]) '[23.670000000000002, 23.969999999999999, 23.870000000000001]' I don't want to have external dependencies, so I prefer to stick with the standard json module. How can I achieve this?
NOTE: This does not work in any recent version of Python. Unfortunately, I believe you have to do this by monkey-patching (which, to my opinion, indicates a design defect in the standard library json package). E.g., this code: import json from json import encoder encoder.FLOAT_REPR = lambda o: format(o, '.2f') print(json.dumps(23.67)) print(json.dumps([23.67, 23.97, 23.87])) emits: 23.67 [23.67, 23.97, 23.87] as you desire. Obviously, there should be an architected way to override FLOAT_REPR so that EVERY representation of a float is under your control if you wish it to be; but unfortunately that's not how the json package was designed.