从__new__返回None是否可以? [英] Is it ok to return None from __new__?

问题描述

通常，如果类的用户知道有时构造函数将评估为None，则从__new__方法返回None是否合理?

In general, is it reasonable to return None from a __new__ method if the user of the class knows that sometimes the constructor will evaluate to None?

文档并不意味着它是非法的，而且我也看不到任何直接的问题(因为不会调用__init__，没有一个不是所讨论的自定义类的实例！).但我担心

The documentation doesn't imply it's illegal, and I don't see any immediate problems (since __init__ is not going to be called, None not being an instance of the custom class in question!). But I'm worried about

1. 是否还有其他不可预见的问题
2. 让构造函数返回None是否是一种好的编程习惯

具体示例:

class MyNumber(int):
    def __new__(cls, value): # value is a string (usually) parsed from a file
        if value == 'N.A.':
            return None
        return int.__new__(cls, value)

推荐答案

这不是非法的.如果结果没有任何奇怪的事情，它将起作用.

It's not illegal. If nothing weird is done with the result, it will work.

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