如何更改可序列化python对象的json编码行为？

3条回答

网友

1楼 · 编辑于 2024-05-29 05:42:22

FastTurtle的答案可能是一个更干净的解决方案。

根据我在问答中解释的技巧，这里有一些接近你想要的东西：Overriding nested JSON encoding of inherited default supported objects like dict, list

import json
import datetime


class mDict(dict):
    pass


class mList(list):
    pass


class JsonDebugEncoder(json.JSONEncoder):
    def _iterencode(self, o, markers=None):
        if isinstance(o, mDict):
            yield '{"__mDict__": '
            # Encode dictionary
            yield '{"orig": '
            for chunk in super(JsonDebugEncoder, self)._iterencode(o, markers):
                yield chunk
            yield ', '
            # / End of Encode dictionary
            # Encode attributes
            yield '"attr": '
            for key, value in o.__dict__.iteritems():
                yield '{"' + key + '": '
                for chunk in super(JsonDebugEncoder, self)._iterencode(value, markers):
                    yield chunk
                yield '}'
            yield '}'
            # / End of Encode attributes
            yield '}'
        elif isinstance(o, mList):
            yield '{"__mList__": '
            # Encode list
            yield '{"orig": '
            for chunk in super(JsonDebugEncoder, self)._iterencode(o, markers):
                yield chunk
            yield ', '
            # / End of Encode list
            # Encode attributes
            yield '"attr": '
            for key, value in o.__dict__.iteritems():
                yield '{"' + key + '": '
                for chunk in super(JsonDebugEncoder, self)._iterencode(value, markers):
                    yield chunk
                yield '}'
            yield '}'
            # / End of Encode attributes
            yield '}'
        else:
            for chunk in super(JsonDebugEncoder, self)._iterencode(o, markers=markers):
                yield chunk

    def default(self, obj):
        if isinstance(obj, datetime.datetime):
            return obj.isoformat()


class JsonDebugDecoder(json.JSONDecoder):
    def decode(self, s):
        obj = super(JsonDebugDecoder, self).decode(s)
        obj = self.recursiveObjectDecode(obj)
        return obj

    def recursiveObjectDecode(self, obj):
        if isinstance(obj, dict):
            decoders = [("__mList__", self.mListDecode),
                        ("__mDict__", self.mDictDecode)]
            for placeholder, decoder in decoders:
                if placeholder in obj:                  # We assume it's supposed to be converted
                    return decoder(obj[placeholder])
                else:
                    for k in obj:
                        obj[k] = self.recursiveObjectDecode(obj[k])
        elif isinstance(obj, list):
            for x in range(len(obj)):
                obj[x] = self.recursiveObjectDecode(obj[x])
        return obj

    def mDictDecode(self, o):
        res = mDict()
        for key, value in o['orig'].iteritems():
            res[key] = self.recursiveObjectDecode(value)
        for key, value in o['attr'].iteritems():
            res.__dict__[key] = self.recursiveObjectDecode(value)
        return res

    def mListDecode(self, o):
        res = mList()
        for value in o['orig']:
            res.append(self.recursiveObjectDecode(value))
        for key, value in o['attr'].iteritems():
            res.__dict__[key] = self.recursiveObjectDecode(value)
        return res


def test_debug_json():
    games = mList(['mario','contra','tetris'])
    games.src = 'console'
    scores = mDict({'dp':10,'pk':45})
    scores.processed = "unprocessed"
    test_json = { 'games' : games, 'scores' : scores ,'date': datetime.datetime.now() }
    jsonDump = json.dumps(test_json, cls=JsonDebugEncoder)
    print jsonDump
    test_pyObject = json.loads(jsonDump, cls=JsonDebugDecoder)
    print test_pyObject

if __name__ == '__main__':
    test_debug_json()

这将导致：

{"date": "2013-05-06T22:28:08.967000", "games": {"__mList__": {"orig": ["mario", "contra", "tetris"], "attr": {"src": "console"}}}, "scores": {"__mDict__": {"orig": {"pk": 45, "dp": 10}, "attr": {"processed": "unprocessed"}}}}

这样您就可以对其进行编码并将其解码回它来自的python对象。

编辑：

这里有一个版本，它实际上编码到你想要的输出，也可以解码它。每当字典包含“orig”和“attr”时，它将检查“orig”是否包含字典或列表，如果包含，则它将分别将对象转换回mdct或mList。

import json
import datetime


class mDict(dict):
    pass


class mList(list):
    pass


class JsonDebugEncoder(json.JSONEncoder):
    def _iterencode(self, o, markers=None):
        if isinstance(o, mDict):    # Encode mDict
            yield '{"orig": '
            for chunk in super(JsonDebugEncoder, self)._iterencode(o, markers):
                yield chunk
            yield ', '
            yield '"attr": '
            for key, value in o.__dict__.iteritems():
                yield '{"' + key + '": '
                for chunk in super(JsonDebugEncoder, self)._iterencode(value, markers):
                    yield chunk
                yield '}'
            yield '}'
            # / End of Encode attributes
        elif isinstance(o, mList):    # Encode mList
            yield '{"orig": '
            for chunk in super(JsonDebugEncoder, self)._iterencode(o, markers):
                yield chunk
            yield ', '
            yield '"attr": '
            for key, value in o.__dict__.iteritems():
                yield '{"' + key + '": '
                for chunk in super(JsonDebugEncoder, self)._iterencode(value, markers):
                    yield chunk
                yield '}'
            yield '}'
        else:
            for chunk in super(JsonDebugEncoder, self)._iterencode(o, markers=markers):
                yield chunk

    def default(self, obj):
        if isinstance(obj, datetime.datetime):    # Encode datetime
            return obj.isoformat()


class JsonDebugDecoder(json.JSONDecoder):
    def decode(self, s):
        obj = super(JsonDebugDecoder, self).decode(s)
        obj = self.recursiveObjectDecode(obj)
        return obj

    def recursiveObjectDecode(self, obj):
        if isinstance(obj, dict):
            if "orig" in obj and "attr" in obj and isinstance(obj["orig"], list):
                return self.mListDecode(obj)
            elif "orig" in obj and "attr" in obj and isinstance(obj['orig'], dict):
                return self.mDictDecode(obj)
            else:
                for k in obj:
                    obj[k] = self.recursiveObjectDecode(obj[k])
        elif isinstance(obj, list):
            for x in range(len(obj)):
                obj[x] = self.recursiveObjectDecode(obj[x])
        return obj

    def mDictDecode(self, o):
        res = mDict()
        for key, value in o['orig'].iteritems():
            res[key] = self.recursiveObjectDecode(value)
        for key, value in o['attr'].iteritems():
            res.__dict__[key] = self.recursiveObjectDecode(value)
        return res

    def mListDecode(self, o):
        res = mList()
        for value in o['orig']:
            res.append(self.recursiveObjectDecode(value))
        for key, value in o['attr'].iteritems():
            res.__dict__[key] = self.recursiveObjectDecode(value)
        return res


def test_debug_json():
    games = mList(['mario','contra','tetris'])
    games.src = 'console'
    scores = mDict({'dp':10,'pk':45})
    scores.processed = "unprocessed"
    test_json = { 'games' : games, 'scores' : scores ,'date': datetime.datetime.now() }
    jsonDump = json.dumps(test_json, cls=JsonDebugEncoder)
    print jsonDump
    test_pyObject = json.loads(jsonDump, cls=JsonDebugDecoder)
    print test_pyObject
    print test_pyObject['games'].src

if __name__ == '__main__':
    test_debug_json()

以下是有关输出的更多信息：

# Encoded
{"date": "2013-05-06T22:41:35.498000", "games": {"orig": ["mario", "contra", "tetris"], "attr": {"src": "console"}}, "scores": {"orig": {"pk": 45, "dp": 10}, "attr": {"processed": "unprocessed"}}}

# Decoded ('games' contains the mList with the src attribute and 'scores' contains the mDict processed attribute)
# Note that printing the python objects doesn't directly show the processed and src attributes, as seen below.
{u'date': u'2013-05-06T22:41:35.498000', u'games': [u'mario', u'contra', u'tetris'], u'scores': {u'pk': 45, u'dp': 10}}

很抱歉有任何不好的命名约定，这是一个快速设置。；）

注意：日期时间不会被解码回python表示。可以通过检查任何名为“date”且包含日期时间的有效字符串表示形式的dict键来实现。

网友

2楼 · 编辑于 2024-05-29 05:42:22

似乎要实现您想要的行为，在给定的限制下，您必须深入研究JSONEncoder类。下面我写了一个定制的JSONEncoder，它重写iterencode方法，将定制的isinstance方法传递给_make_iterencode。它不是世界上最干净的东西，但似乎是最好的选择，它保持定制到最低限度。

# customencoder.py
from json.encoder import (_make_iterencode, JSONEncoder,
                          encode_basestring_ascii, FLOAT_REPR, INFINITY,
                          c_make_encoder, encode_basestring)


class CustomObjectEncoder(JSONEncoder):

    def iterencode(self, o, _one_shot=False):
        """
        Most of the original method has been left untouched.

        _one_shot is forced to False to prevent c_make_encoder from
        being used. c_make_encoder is a funcion defined in C, so it's easier
        to avoid using it than overriding/redefining it.

        The keyword argument isinstance for _make_iterencode has been set
        to self.isinstance. This allows for a custom isinstance function
        to be defined, which can be used to defer the serialization of custom
        objects to the default method.
        """
        # Force the use of _make_iterencode instead of c_make_encoder
        _one_shot = False

        if self.check_circular:
            markers = {}
        else:
            markers = None
        if self.ensure_ascii:
            _encoder = encode_basestring_ascii
        else:
            _encoder = encode_basestring
        if self.encoding != 'utf-8':
            def _encoder(o, _orig_encoder=_encoder, _encoding=self.encoding):
                if isinstance(o, str):
                    o = o.decode(_encoding)
                return _orig_encoder(o)

        def floatstr(o, allow_nan=self.allow_nan,
                     _repr=FLOAT_REPR, _inf=INFINITY, _neginf=-INFINITY):
            if o != o:
                text = 'NaN'
            elif o == _inf:
                text = 'Infinity'
            elif o == _neginf:
                text = '-Infinity'
            else:
                return _repr(o)

            if not allow_nan:
                raise ValueError(
                    "Out of range float values are not JSON compliant: " +
                    repr(o))

            return text

        # Instead of forcing _one_shot to False, you can also just
        # remove the first part of this conditional statement and only
        # call _make_iterencode
        if (_one_shot and c_make_encoder is not None
                and self.indent is None and not self.sort_keys):
            _iterencode = c_make_encoder(
                markers, self.default, _encoder, self.indent,
                self.key_separator, self.item_separator, self.sort_keys,
                self.skipkeys, self.allow_nan)
        else:
            _iterencode = _make_iterencode(
                markers, self.default, _encoder, self.indent, floatstr,
                self.key_separator, self.item_separator, self.sort_keys,
                self.skipkeys, _one_shot, isinstance=self.isinstance)
        return _iterencode(o, 0)

现在可以对CustomObjectEncoder进行子类化，以便它正确地序列化您的自定义对象。CustomObjectEncoder也可以做一些很酷的事情，比如处理嵌套对象。

# test.py
import json
import datetime
from customencoder import CustomObjectEncoder


class MyEncoder(CustomObjectEncoder):

    def isinstance(self, obj, cls):
        if isinstance(obj, (mList, mDict)):
            return False
        return isinstance(obj, cls)

    def default(self, obj):
        """
        Defines custom serialization.

        To avoid circular references, any object that will always fail
        self.isinstance must be converted to something that is
        deserializable here.
        """
        if isinstance(obj, datetime.datetime):
            return obj.isoformat()
        elif isinstance(obj, mDict):
            return {"orig": dict(obj), "attrs": vars(obj)}
        elif isinstance(obj, mList):
            return {"orig": list(obj), "attrs": vars(obj)}
        else:
            return None


class mList(list):
    pass


class mDict(dict):
    pass


def main():
    zelda = mList(['zelda'])
    zelda.src = "oldschool"
    games = mList(['mario', 'contra', 'tetris', zelda])
    games.src = 'console'
    scores = mDict({'dp': 10, 'pk': 45})
    scores.processed = "unprocessed"
    test_json = {'games': games, 'scores': scores,
                 'date': datetime.datetime.now()}
    print(json.dumps(test_json, cls=MyEncoder))

if __name__ == '__main__':
    main()

网友

3楼 · 编辑于 2024-05-29 05:42:22

正如其他人已经指出的那样，默认处理程序只对不属于已识别类型的值进行调用。我建议的解决方案是预处理要序列化的对象，在列表、元组和字典上递归，但在自定义类中包装其他值。

像这样的：

def debug(obj):
    class Debug:
        def __init__(self,obj):
            self.originalObject = obj
    if obj.__class__ == list:
        return [debug(item) for item in obj]
    elif obj.__class__ == tuple:
        return (debug(item) for item in obj)
    elif obj.__class__ == dict:
        return dict((key,debug(obj[key])) for key in obj)
    else:
        return Debug(obj)

在将对象传递到json.dumps之前，您可以调用此函数，如下所示：

test_json = debug(test_json)
print(json.dumps(test_json,default=json_debug_handler))

请注意，此代码正在检查类与列表、元组或字典完全匹配的对象，因此从这些类型扩展的任何自定义对象都将被包装而不是解析。因此，常规列表、元组和字典将像往常一样序列化，但所有其他值都将传递给默认处理程序。

所有这些操作的最终结果是，确保每个到达默认处理程序的值都包装在这些调试类中的一个中。因此，首先要做的是提取原始对象，如下所示：

obj = obj.originalObject

然后可以检查原始对象的类型，并处理需要特殊处理的类型。对于其他一切，您应该只返回原始对象（因此处理程序的最后一个返回应该是return obj，而不是return None）。

def json_debug_handler(obj):
    obj = obj.originalObject      # Add this line
    print("object received:")
    print type(obj)
    print("\n\n")
    if  isinstance(obj, datetime.datetime):
        return obj.isoformat()
    elif isinstance(obj,mDict):
        return {'orig':obj, 'attrs': vars(obj)}
    elif isinstance(obj,mList):
        return {'orig':obj, 'attrs': vars(obj)}
    else:
        return obj                # Change this line

请注意，此代码不会检查不可序列化的值。这些将通过最后的return obj，然后将被序列化程序拒绝，并再次传递回默认处理程序-只是这次没有调试包装器。

如果需要处理该场景，可以在处理程序的顶部添加一个检查，如下所示：

if not hasattr(obj, 'originalObject'):
    return None

视频演示：http://ideone.com/tOloNq

演示：http://ideone.com/hQJnLy

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