Question

我正在尝试将一个对象的__dict__序列化为JSON，这是正常工作的，直到我将对象追加到我的第一个对象的一个实例属性中：

from json import dumps

class A(object):
    def __init__(self):
        self.b_list = []

class B(object):
    def __init__(self):
        self.x = 'X'
        self.y = 'Y'
    def __repr__(self):
        return dumps(self.__dict__)

a = A()

print dumps(a.__dict__)  # works fine

a.b_list.append(B())

print dumps(a.__dict__)

第二次来电dumps时，我收到了以下TypeError：

TypeError: {"y": "Y", "x": "X"} is not JSON serializable

我不明白为什么我会一直收到此错误，而我却无法理解为什么这不能通过JSON序列化。

Answer 1

那是因为B的实例不是简单类型。因为您提供了B __repr__方法，所以实例打印，因为它是JSON表示，但它本身不是受支持的JSON类型。

删除__repr__方法，并且回溯不那么令人困惑：

>>> class A(object):
...     def __init__(self):
...         self.b_list = []
... 
>>> class B(object):
...     def __init__(self):
...         self.x = 'X'
...         self.y = 'Y'
... 
>>> a = A()
>>> a.b_list.append(B())
>>> 
>>> print dumps(a.__dict__)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/Users/mj/Development/Library/buildout.python/parts/opt/lib/python2.7/json/__init__.py", line 243, in dumps
    return _default_encoder.encode(obj)
  File "/Users/mj/Development/Library/buildout.python/parts/opt/lib/python2.7/json/encoder.py", line 207, in encode
    chunks = self.iterencode(o, _one_shot=True)
  File "/Users/mj/Development/Library/buildout.python/parts/opt/lib/python2.7/json/encoder.py", line 270, in iterencode
    return _iterencode(o, 0)
  File "/Users/mj/Development/Library/buildout.python/parts/opt/lib/python2.7/json/encoder.py", line 184, in default
    raise TypeError(repr(o) + " is not JSON serializable")
TypeError: <__main__.B object at 0x10a753e10> is not JSON serializable

使用default关键字参数对自定义对象进行编码：

def encode_b(obj):
    if isinstance(obj, B):
        return obj.__dict__
    return obj

json.dumps(a, default=encode_b)

演示：

>>> def encode_b(obj):
...     if isinstance(obj, B):
...         return obj.__dict__
...     return obj
... 
>>> dumps(a.__dict__, default=encode_b)
'{"b_list": [{"y": "Y", "x": "X"}]}'

Python将对象列表序列化为JSON

1 个答案: