更改非 JSON 可序列化对象的格式很容易,例如 datetime.datetime。
出于调试目的,我的要求是改变一些自定义对象从基础对象扩展的方式,例如 dict
和 list
,以 json 格式序列化。代码:
import datetime
import json
def json_debug_handler(obj):
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 None
class mDict(dict):
pass
class mList(list):
pass
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() }
print(json.dumps(test_json,default=json_debug_handler))
if __name__ == '__main__':
test_debug_json()
输出:
{"date": "2013-05-07T01:03:13.098727", "games": ["mario", "contra", "tetris"], "scores": {"pk": 45,“DP”:10}}
期望的输出:
{"date": "2013-05-07T01:03:13.098727", "games": { "orig": ["mario", "contra", "tetris"] "attrs": { "src":"console"}} , "scores": { "orig": {"pk": 45, "dp": 10},"attrs":
"已处理":"未处理 }}
default
处理程序是否不适用于可序列化对象?
如果没有,我该如何覆盖它,而不向扩展类添加 toJSON 方法?
另外,还有这个版本的 JSON 编码器不工作:
class JsonDebugEncoder(json.JSONEncoder):
def default(self,obj):
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 json.JSONEncoder.default(self, obj)
如果有 pickle,__getstate__,__setstate__,
然后在 pickle.loads 对象上使用 json.dumps 的 hack,我也对此持开放态度,我试过了,但这没有用.
最佳答案
似乎要在给定的限制下实现您想要的行为,您必须深入研究 JSONEncoder
类。下面我写了一个自定义 JSONEncoder
覆盖 iterencode
方法将自定义 isinstance
方法传递给 _make_iterencode
.它不是世界上最干净的东西,但考虑到选项,它似乎是最好的,并且它将定制化程度降至最低。
# 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)
您现在可以对 CustomObjectEncoder
进行子类化,以便它正确地序列化您的自定义对象。 CustomObjectEncoder
还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()
https://stackoverflow.com/questions/16405969/
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