Python到JSON的序列化在十进制上失败 [英] Python to JSON Serialization fails on Decimal

问题描述

我有一个包含一些小数的python对象.这导致json.dumps()损坏.

I have a python object which includes some decimals. This is causing the json.dumps() to break.

我从SO中获得了以下解决方案(例如 Python JSON序列化Decimal对象)但是 建议的解决方案仍然不起作用. Python网站-答案完全相同.

I got the following solution from SO (e.g. Python JSON serialize a Decimal object) but the recoomended solution still does not work. Python website - has the exact same answer.

有什么建议可以做到这一点吗?

Any suggestions how to make this work?

谢谢.下面是我的代码.看起来dumps()甚至都没有进入专门的编码器.

Thanks. Below is my code. It looks like the dumps() doesn't even go into the specialized encoder.

clayton@mserver:~/python> cat test1.py
import json, decimal

class DecimalEncoder(json.JSONEncoder):
        def _iterencode(self, o, markers=None):
                print "here we go o is a == ", type(o)
                if isinstance(o, decimal.Decimal):
                        print "woohoo! got a decimal"
                        return (str(o) for o in [o])
                return super(DecimalEncoder, self)._iterencode(o, markers)

z = json.dumps( {'x': decimal.Decimal('5.5')}, cls=DecimalEncoder )
print z
clayton@mserver:~/python> python test1.py
Traceback (most recent call last):
  File "test1.py", line 11, in <module>
    z = json.dumps( {'x': decimal.Decimal('5.5')}, cls=DecimalEncoder )
  File "/home/clayton/python/Python-2.7.3/lib/python2.7/json/__init__.py", line 238, in dumps
    **kw).encode(obj)
  File "/home/clayton/python/Python-2.7.3/lib/python2.7/json/encoder.py", line 201, in encode
    chunks = self.iterencode(o, _one_shot=True)
  File "/home/clayton/python/Python-2.7.3/lib/python2.7/json/encoder.py", line 264, in iterencode
    return _iterencode(o, 0)
  File "/home/clayton/python/Python-2.7.3/lib/python2.7/json/encoder.py", line 178, in default
    raise TypeError(repr(o) + " is not JSON serializable")
TypeError: Decimal('5.5') is not JSON serializable
clayton@mserver:~/python>

推荐答案

不(不再)建议您创建一个子类； json.dump()和json.dumps()函数采用default函数:

It is not (no longer) recommended you create a subclass; the json.dump() and json.dumps() functions take a default function:

def decimal_default(obj):
    if isinstance(obj, decimal.Decimal):
        return float(obj)
    raise TypeError

json.dumps({'x': decimal.Decimal('5.5')}, default=decimal_default)

演示:

>>> def decimal_default(obj):
...     if isinstance(obj, decimal.Decimal):
...         return float(obj)
...     raise TypeError
... 
>>> json.dumps({'x': decimal.Decimal('5.5')}, default=decimal_default)
'{"x": 5.5}'

您发现的代码仅适用于Python 2.6，并且覆盖了在以后的版本中不再调用的私有方法.

The code you found only worked on Python 2.6 and overrides a private method that is no longer called in later versions.

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