Question

我无法理解object_hook函数解析json.loads提供的json的方式。

请考虑以下事项：

import json

j = '{"key": "Program1",\
    "value": {"codes": [], "name": "John Doe", "cities": ["New York", "Houston"]}}'

class Humans:
    def __init__(self, source, codes, name, cities):
        self.source = source
        self.codes = codes
        self.name = name
        self.cities = cities

def as_Humans(dct):
    print(dct)
    source = dct['key']
    value = dct['value']
    codes = value['codes']
    name = value['name']
    cities = value['cities']
    return(Humans(source, codes, name, cities))


print(json.loads(j))
human = json.loads(j, object_hook = as_Humans)        
print(human.name)

当我运行此操作时，我收到以下错误：

{'key': 'Program1', 'value': {'name': 'John Doe', 'cities': ['New York', 'Houston'], 'codes': []}}
{'name': 'John Doe', 'cities': ['New York', 'Houston'], 'codes': []}
Traceback (most recent call last):
  File "stackoverflow.py", line 25, in <module>
    human = json.loads(j, object_hook = as_Humans)        
  File "/usr/lib/python3.4/json/__init__.py", line 331, in loads
    return cls(**kw).decode(s)
  File "/usr/lib/python3.4/json/decoder.py", line 343, in decode
    obj, end = self.raw_decode(s, idx=_w(s, 0).end())
  File "/usr/lib/python3.4/json/decoder.py", line 359, in raw_decode
    obj, end = self.scan_once(s, idx)
  File "stackoverflow.py", line 16, in as_Humans
    source = dct['key']
KeyError: 'key'

显然这不符合我认为的方式：从钩子中的print(dct)，我可以看到只有原始json的一部分被传递，并且因为那部分没有密钥＆＃34;键＆＃34;，好吧，我收到一个关键错误。

如果我修改它以便在json中只有{"codes": [], "name": "John Doe", "cities": ["New York", "Houston"]}（并相应地修改其他所有内容），它就可以工作。

有趣的是，如果json是'{"value": {"codes": [], "name": "John Doe", "cities": ["New York", "Houston"]}}'，它会以相同的方式失败（关键错误＆＃34;值＆＃34;）。

我错过了什么？我的JSON字符串无效吗？是否可以在不首先调整json的情况下执行此操作？

Answer 1

object_hook适用于嵌套在json中的每个对象/ dict，从最深到最高。所以首先向钩子提供{"codes": [], "name": "John Doe", "cities": ["New York", "Houston"]}。

您的示例可以使用以下object_hook修复：

def as_humans(dct):
    if not 'key' in dct:
        print("IT'S A NOT HUMAN", dct)
        return dct
    print("IT'S A HUMAN", dct)
    source = dct['key']
    value = dct['value']
    codes = value['codes']
    name = value['name']
    cities = value['cities']
    return (Humans(source, codes, name, cities))

，输出将是：

{'value': {'cities': ['New York', 'Houston'], 'name': 'John Doe', 'codes': []}, 'key': 'Program1'}
IT'S A NOT HUMAN {'cities': ['New York', 'Houston'], 'name': 'John Doe', 'codes': []}
IT'S A HUMAN {'value': {'cities': ['New York', 'Houston'], 'name': 'John Doe', 'codes': []}, 'key': 'Program1'}
John Doe

object_hook没有解决完整的json

1 个答案: