如何使一个Python类序列化?
class FileItem:
def __init__(self, fname):
self.fname = fname
尝试序列化为JSON:
>>> import json
>>> x = FileItem('/foo/bar')
>>> json.dumps(x)
TypeError: Object of type 'FileItem' is not JSON serializable
如何使一个Python类序列化?
class FileItem:
def __init__(self, fname):
self.fname = fname
尝试序列化为JSON:
>>> import json
>>> x = FileItem('/foo/bar')
>>> json.dumps(x)
TypeError: Object of type 'FileItem' is not JSON serializable
当前回答
加拉科给出了一个非常简洁的答案。我需要修复一些小的东西,但这是有效的:
Code
# Your custom class
class MyCustom(object):
def __json__(self):
return {
'a': self.a,
'b': self.b,
'__python__': 'mymodule.submodule:MyCustom.from_json',
}
to_json = __json__ # supported by simplejson
@classmethod
def from_json(cls, json):
obj = cls()
obj.a = json['a']
obj.b = json['b']
return obj
# Dumping and loading
import simplejson
obj = MyCustom()
obj.a = 3
obj.b = 4
json = simplejson.dumps(obj, for_json=True)
# Two-step loading
obj2_dict = simplejson.loads(json)
obj2 = MyCustom.from_json(obj2_dict)
# Make sure we have the correct thing
assert isinstance(obj2, MyCustom)
assert obj2.__dict__ == obj.__dict__
注意,加载需要两个步骤。现在是__python__属性 未使用。
这种情况有多普遍?
使用AlJohri的方法,我检查了流行的方法:
序列化(Python -> JSON):
To_json: 266,595 on 2018-06-27 toJSON: 96,307 on 2018-06-27 __json__: 8504 on 2018-06-27 For_json: 6937 on 2018-06-27
反序列化(JSON -> Python):
From_json: 226,101 on 2018-06-27
其他回答
这是我的3美分… 这演示了一个树状python对象的显式json序列化。 注意:如果你真的想要这样的代码,你可以使用twisted FilePath类。
import json, sys, os
class File:
def __init__(self, path):
self.path = path
def isdir(self):
return os.path.isdir(self.path)
def isfile(self):
return os.path.isfile(self.path)
def children(self):
return [File(os.path.join(self.path, f))
for f in os.listdir(self.path)]
def getsize(self):
return os.path.getsize(self.path)
def getModificationTime(self):
return os.path.getmtime(self.path)
def _default(o):
d = {}
d['path'] = o.path
d['isFile'] = o.isfile()
d['isDir'] = o.isdir()
d['mtime'] = int(o.getModificationTime())
d['size'] = o.getsize() if o.isfile() else 0
if o.isdir(): d['children'] = o.children()
return d
folder = os.path.abspath('.')
json.dump(File(folder), sys.stdout, default=_default)
为了在10年前的火灾中再添加一个日志,我还将为这个任务提供数据类向导,假设您使用的是Python 3.6+。这可以很好地用于数据类,这实际上是3.7+版本的python内置模块。
dataclass-wizard库将把对象(及其所有属性递归地)转换为dict,并使用fromdict使反向(反序列化)非常简单。另外,这里是PyPi链接:https://pypi.org/project/dataclass-wizard/。
import dataclass_wizard
import dataclasses
@dataclasses.dataclass
class A:
hello: str
a_field: int
obj = A('world', 123)
a_dict = dataclass_wizard.asdict(obj)
# {'hello': 'world', 'aField': 123}
或者如果你想要一个字符串:
a_str = jsons.dumps(dataclass_wizard.asdict(obj))
或者您的类是否从dataclass_wizard扩展。JSONWizard:
a_str = your_object.to_json()
最后,标准库还支持Union类型的数据类,这基本上意味着可以将dict反序列化为类C1或C2的对象。例如:
from dataclasses import dataclass
from dataclass_wizard import JSONWizard
@dataclass
class Outer(JSONWizard):
class _(JSONWizard.Meta):
tag_key = 'tag'
auto_assign_tags = True
my_string: str
inner: 'A | B' # alternate syntax: `inner: typing.Union['A', 'B']`
@dataclass
class A:
my_field: int
@dataclass
class B:
my_field: str
my_dict = {'myString': 'test', 'inner': {'tag': 'B', 'myField': 'test'}}
obj = Outer.from_dict(my_dict)
# True
assert repr(obj) == "Outer(my_string='test', inner=B(my_field='test'))"
obj.to_json()
# {"myString": "test", "inner": {"myField": "test", "tag": "B"}}
加拉科给出了一个非常简洁的答案。我需要修复一些小的东西,但这是有效的:
Code
# Your custom class
class MyCustom(object):
def __json__(self):
return {
'a': self.a,
'b': self.b,
'__python__': 'mymodule.submodule:MyCustom.from_json',
}
to_json = __json__ # supported by simplejson
@classmethod
def from_json(cls, json):
obj = cls()
obj.a = json['a']
obj.b = json['b']
return obj
# Dumping and loading
import simplejson
obj = MyCustom()
obj.a = 3
obj.b = 4
json = simplejson.dumps(obj, for_json=True)
# Two-step loading
obj2_dict = simplejson.loads(json)
obj2 = MyCustom.from_json(obj2_dict)
# Make sure we have the correct thing
assert isinstance(obj2, MyCustom)
assert obj2.__dict__ == obj.__dict__
注意,加载需要两个步骤。现在是__python__属性 未使用。
这种情况有多普遍?
使用AlJohri的方法,我检查了流行的方法:
序列化(Python -> JSON):
To_json: 266,595 on 2018-06-27 toJSON: 96,307 on 2018-06-27 __json__: 8504 on 2018-06-27 For_json: 6937 on 2018-06-27
反序列化(JSON -> Python):
From_json: 226,101 on 2018-06-27
正如在许多其他答案中提到的,您可以将函数传递给json。转储将不是默认支持的类型之一的对象转换为受支持的类型。令人惊讶的是,他们都没有提到最简单的情况,即使用内置函数vars将对象转换为包含其所有属性的dict:
json.dumps(obj, default=vars)
注意,这只涵盖了基本的情况,如果你需要对某些类型进行更具体的序列化(例如排除某些属性或没有__dict__属性的对象),你需要使用自定义函数或JSONEncoder,如其他答案中所述。
基于Quinten Cabo的回答:
def sterilize(obj):
"""Make an object more ameniable to dumping as json
"""
if type(obj) in (str, float, int, bool, type(None)):
return obj
elif isinstance(obj, dict):
return {k: sterilize(v) for k, v in obj.items()}
list_ret = []
dict_ret = {}
for a in dir(obj):
if a == '__iter__' and callable(obj.__iter__):
list_ret.extend([sterilize(v) for v in obj])
elif a == '__dict__':
dict_ret.update({k: sterilize(v) for k, v in obj.__dict__.items() if k not in ['__module__', '__dict__', '__weakref__', '__doc__']})
elif a not in ['__doc__', '__module__']:
aval = getattr(obj, a)
if type(aval) in (str, float, int, bool, type(None)):
dict_ret[a] = aval
elif a != '__class__' and a != '__objclass__' and isinstance(aval, type):
dict_ret[a] = sterilize(aval)
if len(list_ret) == 0:
if len(dict_ret) == 0:
return repr(obj)
return dict_ret
else:
if len(dict_ret) == 0:
return list_ret
return (list_ret, dict_ret)
区别在于
Works for any iterable instead of just list and tuple (it works for NumPy arrays, etc.) Works for dynamic types (ones that contain a __dict__). Includes native types float and None so they don't get converted to string. Classes that have __dict__ and members will mostly work (if the __dict__ and member names collide, you will only get one - likely the member) Classes that are lists and have members will look like a tuple of the list and a dictionary Python3 (that isinstance() call may be the only thing that needs changing)