为什么我不能子类化 datetime.date? [英] Why can't I subclass datetime.date?
问题描述
为什么以下内容不起作用(Python 2.5.2)?
<预><代码>>>>导入日期时间>>>D类(日期时间.日期):def __init__(self, year):datetime.date.__init__(self, year, 1, 1)>>>D(2008)回溯(最近一次调用最后一次):文件<stdin>",第 1 行,在 <module> 中类型错误:函数正好需要 3 个参数(给定 1 个)我想创建一个类似于 datetime.date
的类,但具有不同的 __init__
函数.显然我的函数永远不会被调用.相反,原始的 datetime.date.__init__
被调用并失败,因为它需要 3 个参数,而我传入了一个.
这是怎么回事?这是线索吗?
<预><代码>>>>日期时间.日期.__init__<'object'对象的槽包装器'__init__'>谢谢!
关于其他几个答案,这与在 C 中实现的日期本身没有任何关系.__init__
方法什么都不做,因为它们是 immutable 对象,因此构造函数 (__new__
) 应该完成所有工作.你会看到相同的行为子类化 int、str 等.
Why doesn't the following work (Python 2.5.2)?
>>> import datetime
>>> class D(datetime.date):
def __init__(self, year):
datetime.date.__init__(self, year, 1, 1)
>>> D(2008)
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: function takes exactly 3 arguments (1 given)
I wanted to create a class that was just like datetime.date
, but with a different __init__
function. Apparently my function never gets called. Instead the original datetime.date.__init__
is called and fails because that expects 3 arguments and I am passing in one.
What's going on here? And is this a clue?
>>> datetime.date.__init__
<slot wrapper '__init__' of 'object' objects>
Thanks!
Regarding several other answers, this doesn't have anything to do with dates being implemented in C per se. The __init__
method does nothing because they are immutable objects, therefore the constructor (__new__
) should do all the work. You would see the same behavior subclassing int, str, etc.
>>> import datetime
>>> class D(datetime.date):
def __new__(cls, year):
return datetime.date.__new__(cls, year, 1, 1)
>>> D(2008)
D(2008, 1, 1)
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