如何用自己的方法扩展Python的datetime.datetime？ [英] How can I extend Python's datetime.datetime with my own methods?

问题描述

我正在尝试使用几种额外的方法来扩展Python的 datetime.datetime 类。所以，例如我在做：

I'm trying to extend Python's datetime.datetime class with a couple of extra methods. So, for example I'm doing:

import datetime

class DateTime(datetime.datetime):
    def millisecond(self):
        return self.microsecond/1000

但是如果我这样做

>>> d = DateTime(2010, 07, 11, microsecond=3000)
>>> print d.millisecond()
3
>>> delta = datetime.timedelta(hours=4)
>>> newd = d + delta
>>> print newd.millisecond()
AttributeError: 'datetime.datetime' object has no attribute 'millisecond'

这显然是因为 d + delta 调用 datetime.datetime .__ add __（）方法返回一个

This is obviously because doing d + delta calls the datetime.datetime.__add__() method which returns a datetime.datetime object.

有什么办法可以让这个 datetime.datetime 对象转换为 DateTime 对象？或者我必须重新实现我的 DateTime 子类中的所有运算符才能返回正确的类型？

Is there any way I can make this datetime.datetime object convert to a DateTime object? Or would I have to reimplement all the operators in my DateTime subclass to return the correct type?

推荐答案

在这种情况下，我喜欢简单的独立功能：

In this case I'd prefer simple free-standing functions:

import datetime
def millisecond(dt):
    return dt.microsecond/1000

（见评论），但我认为在这种情况下，它们是多余的。

Mixins are possible in Python (see the comment), but I think in such cases they are superfluous.

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