无法腌制日期时间子类

Question

我正在尝试 pickle 和 unpickle 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，也不知道如何解决。这是最小的例子：

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)

有谁知道问题出在哪里以及如何解决？

Answer 1

根据 Pickling Class Instances section of the pickle module's documentation 中的信息，我能够使以下工作正常进行。从已添加的 __reduce_ex__() 方法返回的值的元组将导致 __new__() 构造函数在 class 实例被 pickle.loads() 调用 unpickled 时被调用——就像当您调用 class.

时通常会发生什么

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

另请注意，由于您的 leap_year 参数已被问题中的实现忽略（并且不清楚为什么无论如何都需要将其传递给初始化程序），我已将其替换为a Python property 根据当前实例的年份值为其动态计算一个布尔值。

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

无法腌制日期时间子类

Unable to pickle datetime subclass

python

datetime

pickle

python-datetime