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Date: Mon, 26 Dec 2011 00:35:46 +1100
Subject: Re: Test None for an object that does not implement ==
From: Chris Angelico <rosuav@gmail.com>
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Xref: x330-a1.tempe.blueboxinc.net comp.lang.python:17893

On Mon, Dec 26, 2011 at 12:17 AM, Roy Smith <roy@panix.com> wrote:
> Just for fun, I tried playing around with subclassing NoneType and
> writing an __eq__ for my subclass. =A0Turns out, you can't do that:
>
> Traceback (most recent call last):
> =A0File "./none.py", line 5, in <module>
> =A0 =A0class Nihil(NoneType):
> TypeError: Error when calling the metaclass bases
> =A0 =A0type 'NoneType' is not an acceptable base type

Yes; unfortunately quite a few Python built-in classes can't be
subclassed. It's an unfortunate fact of implementation, I think,
rather than a deliberate rule.

But then, what would you ever need to subclass None for, other than
toys and testing?

ChrisA