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python - 无法腌制日期时间子类

问题描述

我正在尝试腌制和取消腌制datetime.datetime子类对象。但是，它总是会产生错误，我不知道为什么会这样以及如何解决它。这是最小的示例：

from datetime import datetime, date, time 
class A(datetime):
    def __new__(cls, year = 2016, month=1, day=1, hour=0, minute=0, leap_year=False):
        return datetime.__new__(cls, year ,month, day, hour, minute)

import pickle
obj = A( month=1, day=1, hour=1, leap_year = False)
serial = pickle.dumps(obj, protocol=pickle.HIGHEST_PROTOCOL)
unpickle = pickle.loads( serial, encoding='bytes')

这将给出以下错误：

TypeError                                 Traceback (most recent call last)
<ipython-input-2-12195a09d83d> in <module>()
      5 
      6 
----> 7 unpickle = pickle.loads( serial, encoding='bytes')

<ipython-input-1-605483566b52> in __new__(cls, year, month, day, hour, minute, leap_year)
      2 class A(datetime):
      3     def __new__(cls, year = 2016, month=1, day=1, hour=0, minute=0, leap_year=False):
----> 4         return datetime.__new__(cls, year ,month, day, hour, minute)
      5 

TypeError: an integer is required (got type bytes)

有谁知道问题可能出在哪里以及如何解决？

标签： pythondatetimepicklepython-datetime

解决方案

根据模块文档的Pickling Class Instances部分中的信息，我能够完成以下工作。从已添加的方法返回的值的元组将导致在调用取消调用类实例时调用构造函数——就像调用类时通常发生的情况一样。pickle__reduce_ex__()__new__()pickle.loads()

请注意，我不需要知道是否或如何datetime自定义酸洗，也不需要了解它的 C 实现。

另请注意，由于leap_year您的问题中的实现忽略了您的参数（并且尚不清楚为什么无论如何都需要将其传递给初始化程序），因此我已将其替换为 Pythonproperty动态计算布尔值基于当前实例的年份值。

from datetime import datetime, date, time
import pickle


class A(datetime):
    def __new__(cls, year=2016, month=1, day=1, hour=0, minute=0):
        return datetime.__new__(cls, year, month, day, hour, minute)

    def __reduce_ex__(self, protocol):
        return (type(self), (self.year, self.month, self.day, self.hour, self.minute))

    @property
    def is_leapyear(self):
        ''' Determine if specified year is leap year. '''
        year = self.year
        if year % 4 != 0:
            return False
        elif year % 100 != 0:
            return True
        elif year % 400 != 0:
            return False
        else:
            return True

obj = A(month=1, day=1, hour=1, leap_year=False)
print('calling pickle.dumps()')
serial = pickle.dumps(obj, protocol=pickle.HIGHEST_PROTOCOL)
print('calling pickle.loads()')
unpickle = pickle.loads(serial, encoding='bytes')
print('unpickled {!r}'.format(unpickle))  # -> unpickled A(2016, 1, 1, 1, 0)
print('unpickle.is_leapyear: {}'.format(unpickle.is_leapyear))  # -> True

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