带有 simplejson 后端的 jsonpickle 将 Decimal 序列化为 null

Question

我正在尝试在 python 3.7 中使用 jsonpickle 将对象树序列化为 json。但是，所有Decimals 都被序列化为null。我使用 simplejson 作为后端，所以它应该能够序列化小数。

如何将（复杂）对象树序列化为 json，包括小数？

示例代码（需要安装 simplejson 和 jsonpickle）： 预期的序列化 json 应该是 {"amount": 1.0}，我不想使用 float，因为舍入错误。

import jsonpickle
from decimal import Decimal

jsonpickle.set_preferred_backend('simplejson')
jsonpickle.set_encoder_options('simplejson', use_decimal=True)

class MyClass():
    def __init__(self, amount):
        self.amount = amount

    def to_json(self):
        return jsonpickle.dumps(self, unpicklable=False)

if __name__ == '__main__':
    obj = MyClass(Decimal('1.0'))
    print(obj.to_json())  # prints '{"amount": null}'

PS 我不关心使用 jsonpickle。因此，也欢迎使用 jsonpickle 的替代方法将复杂的对象树序列化为 json（包括十进制字段）。

Answer 1

更新答案：jsonpickle 的 master 分支现在有一个 use_decimal 模式，允许您在没有任何自定义处理程序的情况下实现此结果。

import decimal
import unittest

import jsonpickle


class Example(object):
    """Example class holding a Decimal"""

    def __init__(self, amount):
        self.amount = decimal.Decimal(amount)


class UseDecimalTestCase(unittest.TestCase):
    """Demonstrate the new use_decimal mode"""

    def test_use_decimal(self):

        obj = Example(0.5)

        # Configure simplejson to use decimals.
        jsonpickle.set_encoder_options('simplejson', use_decimal=True, sort_keys=True)
        jsonpickle.set_preferred_backend('simplejson')

        as_json = jsonpickle.dumps(obj, unpicklable=False, use_decimal=True)
        print(as_json)
        # {"amount": 0.5}

        # Configure simplejson to get back Decimal when restoring from json.
        jsonpickle.set_decoder_options('simplejson', use_decimal=True)
        obj_clone = jsonpickle.loads(as_json)

        # NOTE: we get back a dict, not an Example instance.
        self.assertTrue(isinstance(obj_clone, dict))
        # But, the Decimal *is* preserved
        self.assertTrue(isinstance(obj_clone['amount'], decimal.Decimal))
        self.assertEqual(obj.amount, obj_clone['amount'])

        # Side-effect of simplejson decimal mode:
        # floats become Decimal when round-tripping
        obj.amount = 0.5  # float
        as_json = jsonpickle.dumps(obj, unpicklable=False)
        obj_clone = jsonpickle.loads(as_json)
        self.assertTrue(isinstance(obj_clone['amount'], decimal.Decimal))


if __name__ == '__main__':
    unittest.main()

相关问题：

https://github.com/jsonpickle/jsonpickle/issues/244

对于较旧的 jsonpickle 版本：

这可以通过允许 simplejson 进行编码的自定义传递处理程序来完成。您必须同时配置编码器和解码器选项，以便获得小数。如果您不关心往返，那么用例会更简单。

import decimal
import unittest

import jsonpickle
from jsonpickle.handlers import BaseHandler


class SimpleDecimalHandler(BaseHandler):
    """Simple pass-through handler so that simplejson can do the encoding"""

    def flatten(self, obj, data):
        return obj

    def restore(self, obj):
        return obj



class Example(object):
    """Example class holding a Decimal"""

    def __init__(self, amount):
        self.amount = decimal.Decimal(amount)



class DecimalTestCase(unittest.TestCase):
    """Test Decimal json serialization"""

    def test_custom_handler(self):

        obj = Example(0.5)

        # Enable the simplejson Decimal handler -- slightly simpler than jsonpickle's
        # default handler which does the right thing already.
        # If you don't care about the json representation then you don't
        # need to do anything -- jsonpickle preserves decimal by default
        # when using its default dumps() options.
        #
        # We use this decimal handler so that simplejson does the encoding
        # rather than jsonpickle.  Thus, we have to configure simplejson too,
        # which is not needed otherwise when using jsonpickle's defaults.

        jsonpickle.set_encoder_options('simplejson', use_decimal=True, sort_keys=True)
        jsonpickle.set_decoder_options('simplejson', use_decimal=True)
        jsonpickle.set_preferred_backend('simplejson')

        SimpleDecimalHandler.handles(decimal.Decimal)
        as_json = jsonpickle.dumps(obj)

        print(as_json)
        # {"amount": 0.5, "py/object": "__main__.Example"}

        # NOTE: this comes back as an Example instance
        clone = jsonpickle.loads(as_json)

        self.assertTrue(isinstance(clone, Example))
        self.assertTrue(isinstance(clone.amount, decimal.Decimal))
        self.assertEqual(obj.amount, clone.amount)


        # We can simplify the JSON representation a little further
        # by using unpickleable=False, but we lose the Example class.
        as_json = jsonpickle.dumps(obj, unpicklable=False)

        # Upside: this prints {"amount": 0.5}
        # Downside: this object cannot be reconstructed back into an
        # instance of the Example class.
        print(as_json)

        # NOTE: we get back a dict, not an Example instance.
        obj_clone = jsonpickle.loads(as_json)
        self.assertTrue(isinstance(obj_clone, dict))

        # But, the Decimal *is* preserved
        self.assertTrue(isinstance(obj_clone['amount'], decimal.Decimal))
        self.assertEqual(obj.amount, obj_clone['amount'])


if __name__ == '__main__':
    unittest.main()

Answer 2

您需要注册一个处理程序来处理 Decimal 类

import jsonpickle
from decimal import Decimal

jsonpickle.set_preferred_backend('simplejson')
jsonpickle.set_encoder_options('simplejson', use_decimal=True)

class DecimalHandler(jsonpickle.handlers.BaseHandler):

    def flatten(self, obj, data):

        return obj.__str__() #Convert to json friendly format

jsonpickle.handlers.registry.register(Decimal, DecimalHandler)

class MyClass():
    def __init__(self, amount):
        self.amount = amount

    def to_json(self):
        return jsonpickle.dumps(self, unpicklable=False)

if __name__ == '__main__':
    obj = MyClass(Decimal('1.0'))
    print(obj.to_json())