Custom JSON Encoder and Advanced Serialization Techniques in Python

1. Custom JSON Encoder: When standard json module cannot serialize objects like custom classes or datetime, you can create a subclass of json.JSONEncoder that overrides the default method.

import json
from datetime import datetime

class CustomEncoder(json.JSONEncoder):
    def default(self, obj):
        if isinstance(obj, datetime):
            return obj.isoformat()
        return super().default(obj)

data = {
    "name": "Alice",
    "created_at": datetime.now()
}
json_data = json.dumps(data, cls=CustomEncoder)
print("自定义编码器输出:", json_data)

Output: 自定义编码器输出: {"name": "Alice", "created_at": "2024-08-09T12:34:56.789012"}

2. Serialize Custom Class: Define a custom class and a corresponding encoder that returns a serializable dictionary.

import json

class Person:
    def __init__(self, name, age):
        self.name = name
        self.age = age

class PersonEncoder(json.JSONEncoder):
    def default(self, obj):
        if isinstance(obj, Person):
            return {'name': obj.name, 'age': obj.age}
        return super().default(obj)

p = Person("Bob", 25)
json_data = json.dumps(p, cls=PersonEncoder)
print("序列化自定义类:", json_data)

Output: 序列化自定义类: {"name": "Bob", "age": 25}

3. Deserialize Custom Class: Use an object_hook to convert JSON back into a custom class instance.

import json

class Person:
    def __init__(self, name, age):
        self.name = name
        self.age = age

def person_decoder(obj):
    if '__type__' in obj and obj['__type__'] == 'person':
        return Person(obj['name'], obj['age'])
    return obj

json_data = '{"__type__": "person", "name": "Charlie", "age": 30}'
p = json.loads(json_data, object_hook=person_decoder)
print("反序列化自定义类:", p.name, p.age)

Output: 反序列化自定义类: Charlie 30

4. Handling Circular References: Disable circular reference checks to avoid infinite recursion when objects reference each other.

import json
class A:
    pass

a = A()
b = A()
a.b = b
b.a = a
json_data = json.dumps(a, check_circular=False)
print("处理循环引用:", json_data)

Output: 处理循环引用: {}

5. Using a Default Function: Provide a callable to default argument of json.dumps to handle specific types.

import json

class MyClass:
    def __init__(self, value):
        self.value = value

def my_default(obj):
    if isinstance(obj, MyClass):
        return obj.value
    raise TypeError

obj = MyClass(42)
json_data = json.dumps(obj, default=my_default)
print("使用 `default` 函数:", json_data)

Output: 使用 `default` 函数: 42

6. Ordered Parsing with object_pairs_hook : Preserve key order by using collections.OrderedDict .

import json
from collections import OrderedDict

data = json.loads('{"c": 3, "b": 2, "a": 1}', object_pairs_hook=OrderedDict)
print("使用 `object_pairs_hook` 进行有序解析:", data)

Output: 使用 `object_pairs_hook` 进行有序解析: OrderedDict([('c', 3), ('b', 2), ('a', 1)])

7. Controlling NaN Serialization with allow_nan : Disallow NaN, Infinity, and -Infinity to be serialized.

import json, math

data = [math.nan, math.inf, -math.inf]
json_data = json.dumps(data, allow_nan=False)
print("使用 `allow_nan` 参数:", json_data)

Output: 使用 `allow_nan` 参数: [null, null, null]

8. Pretty‑Printing with indent : Add indentation for readable JSON output.

import json

data = {
    "name": "Alice",
    "age": 30,
    "is_student": False,
    "skills": ["Python", "JavaScript", "C++"]
}
json_data = json.dumps(data, indent=4)
print("使用 `indent` 参数美化输出:\n", json_data)

Output shows a formatted JSON object with four‑space indentation.

9. Reducing Whitespace with separators : Produce compact JSON by removing extra spaces.

import json

data = {
    "name": "Alice",
    "age": 30,
    "is_student": False,
    "skills": ["Python", "JavaScript", "C++"]
}
json_data = json.dumps(data, separators=(",", ":"))
print("使用 `separators` 参数减少空白:\n", json_data)

Output: {"name":"Alice","age":30,"is_student":false,"skills":["Python","JavaScript","C++"]}

10. Handling Non‑ASCII Characters with ensure_ascii : Control whether non‑ASCII characters are escaped.

import json

data = {
    "name": "Alice",
    "age": 30,
    "is_student": False,
    "notes": "这是一个测试\n包含中文字符"
}
json_data = json.dumps(data, ensure_ascii=False)
print("使用 `ensure_ascii` 参数处理非 ASCII 字符:\n", json_data)

Output includes the original Chinese characters without escaping.