Question

此问题与type evolution with jsonpickle (python)

有关

当前状态说明：

我需要在python中使用jsonpickle将对象存储到JSON文件。

对象类CarState由另一个软件组件的脚本生成，因此我无法更改类本身。此脚本自动为jsonpickle用于序列化对象的类生成__getstate__和__setstate__方法。 __getstate__只返回每个成员变量的值列表，没有字段名称。因此，jsonpickle不会存储字段名称，只会存储JSON数据中的值（请参阅下面的代码示例）

问题：

让我们说我的程序需要通过附加字段（CarState）扩展新版本（版本2）的类CarStateNewVersion。现在，如果它从版本1加载JSON数据，则数据不会分配到正确的字段。

这是一个展示问题的示例代码。类CarState由脚本生成，并在此处简化以显示问题。在版本2中，我使用新字段更新了类CarState（在代码剪辑中插入CarStateNewVersion以保持简单）

#!/usr/bin/env python
import jsonpickle as jp

# Class using slots and implementing the __getstate__ method
# Let's say this is in program version 1
class CarState(object):
    __slots__ = ['company','type']
    _slot_types = ['string','string']

    def __init__(self):
        self.company = ""
        self.type = ""

    def __getstate__(self):
        return [getattr(self, x) for x in self.__slots__]

    def __setstate__(self, state):
        for x, val in zip(self.__slots__, state):
            setattr(self, x, val)

# Class using slots and implementing the __getstate__ method
# For program version 2 a new field 'year' is needed           
class CarStateNewVersion(object):
    __slots__ = ['company','year','type']
    _slot_types = ['string','string','string']

    def __init__(self):
        self.company = ""
        self.type = ""
        self.year = "1900"

    def __getstate__(self):
        return [getattr(self, x) for x in self.__slots__]

    def __setstate__(self, state):
        for x, val in zip(self.__slots__, state):
            setattr(self, x, val)

# Class using slots without the __getstate__ method
# Let's say this is in program version 1            
class CarDict(object):
    __slots__ = ['company','type']
    _slot_types = ['string','string']

    def __init__(self):
        self.company = ""
        self.type = ""

# Class using slots without the __getstate__ method
# For program version 2 a new field 'year' is needed      
class CarDictNewVersion(object):
    __slots__ = ['company','year','type']
    _slot_types = ['string','string','string']

    def __init__(self):
        self.company = ""
        self.type = ""
        self.year = "1900"



if __name__ == "__main__":

    # Version 1 stores the data
    carDict = CarDict()
    carDict.company = "Ford"
    carDict.type = "Mustang"
    print jp.encode(carDict)
    # {"py/object": "__main__.CarDict", "company": "Ford", "type": "Mustang"}

    # Now version 2 tries to load the data
    carDictNewVersion = jp.decode('{"py/object": "__main__.CarDictNewVersion", "company": "Ford", "type": "Mustang"}')
    # OK!
    # carDictNewVersion.company = Ford
    # carDictNewVersion.year = undefined
    # carDictNewVersion.type = Mustang


    # Version 1 stores the data
    carState = CarState()
    carState.company = "Ford"
    carState.type = "Mustang"
    print jp.encode(carState)
    # {"py/object": "__main__.CarState", "py/state": ["Ford", "Mustang"]}

    # Now version 2 tries to load the data    
    carStateNewVersion = jp.decode('{"py/object": "__main__.CarStateNewVersion", "py/state": ["Ford", "Mustang"]}')
    # !!!! ERROR !!!!
    # carDictNewVersion.company = Ford
    # carDictNewVersion.year = Mustang
    # carDictNewVersion.type = undefined
    try:
        carDictNewVersion.year
    except:
        carDictNewVersion.year = 1900

正如您在CarDict和CarDictNewVersion课程中看到的那样，如果__getstate__未实施，则新添加的字段没有问题，因为JSON文本还包含字段名称。

问题：

是否有可能告诉jsonpickle不使用__getstate__并使用__dict__代替在JSON数据中包含字段名称？或者是否有其他可能以某种方式包括字段名称？

注意：我无法更改CarState类或包含__getstate__方法，因为它是通过其他软件组件的脚本生成的。我只能在main方法中更改代码。

或者是否有另一个用于python的序列化工具，它创建了人类可读的输出并包含字段名称？

其他背景信息： 该类是使用ROS中的消息定义生成的，即genpy ，生成的类继承自实现Message的{{1}}类（参见https://github.com/ros/genpy/blob/indigo-devel/src/genpy/message.py#L308）

Answer 1

子类CarState实现自己的pickle协议方法，或者用jsonpickle注册处理程序。

由于类型演变，jsonpickle强制使用dict

1 个答案:

由于类型演变，jsonpickle强制使用__dict__

1 个答案:

由于类型演变，jsonpickle强制使用dict