Python如何将含对象列表的自定义类对象序列化为JSON

运行序列化代码时抛出如下错误：

TypeError: Object of type person is not JSON serializable

问题复现代码 #

import json

class person:
    def __init__(self, name, cars):
        self._name = name
        self._cars = cars
    
class car:
    def __init__(self, brand, color):
        self._brand = brand
        self._color = color

Jason = person("Jason", [car("Toyota", "Blue"), car("Honda", "Red")])

json = json.dumps(Jason)
print(json)

期望输出格式 #

{
    "name": "Jason",
    "cars":[
        {
            "brand": "Toyota",
            "color": "Blue"
        },
        {
            "brand": "Honda",
            "color": "Red"
        }
    ]
}

报错原因 #

Python标准库json模块默认仅支持序列化字典、列表、字符串、数字、布尔值、None这类原生数据类型，无法直接识别自定义类的实例对象，因此抛出类型错误。

可行实现方案 #

以下两种方案均可正常运行，输出符合预期结构的JSON内容：

• 方案1：传入default参数自定义序列化逻辑
  利用json.dumps的default参数，指定遇到非原生类型时的转换规则，无需手动逐层转换嵌套对象：

  import json
  
  class person:
      def __init__(self, name, cars):
          self._name = name
          self._cars = cars
      
  class car:
      def __init__(self, brand, color):
          self._brand = brand
          self._color = color
  
  def serialize_custom(obj):
      if isinstance(obj, person):
          return {"name": obj._name, "cars": obj._cars}
      if isinstance(obj, car):
          return {"brand": obj._brand, "color": obj._color}
      raise TypeError(f"Object of type {type(obj).__name__} is not JSON serializable")
  
  Jason = person("Jason", [car("Toyota", "Blue"), car("Honda", "Red")])
  # indent=4用于格式化输出，匹配预期的缩进结构
  result = json.dumps(Jason, default=serialize_custom, indent=4)
  print(result)
  

• 方案2：给自定义类添加字典转换方法
  如果类需要频繁序列化，可以在类内部实现转字典的方法，序列化时直接调用方法得到原生字典结构再转JSON：

  import json
  
  class person:
      def __init__(self, name, cars):
          self._name = name
          self._cars = cars
      def to_dict(self):
          return {
              "name": self._name,
              "cars": [car_item.to_dict() for car_item in self._cars]
          }
      
  class car:
      def __init__(self, brand, color):
          self._brand = brand
          self._color = color
      def to_dict(self):
          return {"brand": self._brand, "color": self._color}
  
  Jason = person("Jason", [car("Toyota", "Blue"), car("Honda", "Red")])
  result = json.dumps(Jason.to_dict(), indent=4)
  print(result)
  

内容的提问来源于stack exchange，提问作者Olivier Coujan