python中将浮点数变成json时，控制小数位数

>>>import json

>>>d = { ‘a‘: 0.333333333, ‘b‘: 0.445444444, ‘c‘: 0.293 }

>>>json.dumps(d)

得到

‘{"a": 0.333333333, "c": 0.293, "b": 0.445444444}‘

而我们期望得到

‘{"a": 0.33, "c": 0.29, "b": 0.45}‘

以下是解决办法

http://stackoverflow.com/questions/1447287/format-floats-with-standard-json-module

import json

def pretty_floats(obj):
    if isinstance(obj, float):
        return round(obj, 3)
    elif isinstance(obj, dict):
        return dict((k, pretty_floats(v)) for k, v in obj.items())
    elif isinstance(obj, (list, tuple)):
        return map(pretty_floats, obj)
    return obj

d = { ‘a‘: 0.333333333, ‘b‘: 0.445444444, ‘c‘: 0.293 }

print json.dumps(pretty_floats(d))