使用Python> = 2.7将嵌套的namedtuple序列化为JSON

Question

我遇到类似于CalvinKrishy问题的问题 Samplebias的解决方案不能处理我的数据.

我使用的是Python 2.7.

这是数据:

Namedtuple

>>> a_t = namedtuple('a','f1 words')
>>> word_t = namedtuple('word','f2 value')
>>> w1 = word_t(f2=[0,1,2], value='abc')
>>> w2 = word_t(f2=[3,4], value='def')
>>> a1 = a_t(f1=[0,1,2,3,4],words=[w1, w2])
>>> a1
a(f1=[0, 1, 2, 3, 4], words=[word(f2=[0, 1, 2], value='abc'), word(f2=[3, 4], value='def')])

快译通

>>> w3 = {}
>>> w3['f2'] = [0,1,2]
>>> w3['value'] = 'abc'
>>> w4 = {}
>>> w4['f2'] = [3,4]
>>> w4['value'] = 'def'
>>> a2 = {}
>>> a2['f1'] = [0, 1, 2, 3, 4]
>>> a2['words'] = [w3,w4]
>>> a2
{'f1': [0, 1, 2, 3, 4], 'words': [{'f2': [0, 1, 2], 'value': 'abc'}, {'f2': [3, 4], 'value': 'def'}]}

你可以看到a1和a2都是相同的,除了一个是namedtuple而另一个是dict.

但是json.dumps是不同的:

>>> json.dumps(a1._asdict())
'{"f1": [0, 1, 2, 3, 4], "words": [[[0, 1, 2], "abc"], [[3, 4], "def"]]}'
>>> json.dumps(a2)
'{"f1": [0, 1, 2, 3, 4], "words": [{"f2": [0, 1, 2], "value": "abc"}, {"f2": [3, 4], "value": "def"}]}'

我希望a1的json格式与a2的格式完全相同.

Answer 1

问题在于使用namedtuple._asdict,而不是json.dumps.如果您查看代码,namedtuple(..., verbose=True)您会看到:

def _asdict(self):
    'Return a new OrderedDict which maps field names to their values'
    return OrderedDict(zip(self._fields, self))

只有最高级别实际上已更改为OrderedDict,所有包含的元素都保持不变.这意味着嵌套的namedtuples仍然是tuple子类并且(正确地)序列化等等.

如果您可以接受对特定转换函数的调用(如调用_asdict),则可以编写自己的函数.

def namedtuple_asdict(obj):
  if hasattr(obj, "_asdict"): # detect namedtuple
    return OrderedDict(zip(obj._fields, (namedtuple_asdict(item) for item in obj)))
  elif isinstance(obj, basestring): # iterables - strings
     return obj
  elif hasattr(obj, "keys"): # iterables - mapping
     return OrderedDict(zip(obj.keys(), (namedtuple_asdict(item) for item in obj.values())))
  elif hasattr(obj, "__iter__"): # iterables - sequence
     return type(obj)((namedtuple_asdict(item) for item in obj))
  else: # non-iterable cannot contain namedtuples
    return obj

json.dumps(namedtuple_asdict(a1))
# prints '{"f1": [0, 1, 2, 3, 4], "words": [{"f2": [0, 1, 2], "value": "abc"}, {"f2": [3, 4], "value": "def"}]}'

正如您所看到的,最大的问题是嵌套结构不是 namedtuple s但可以包含它们.