Re: A proposal to modify `None` so that it hashes to a constant

You're right of course.  Oh well, it *was* a wild idea.😁
Rob Cliffe

On 04/12/2

On 04/12/2022 18:16, Chris Angelico wrote:
> On Mon, 5 Dec 2022 at 05:11, Rob Cliffe via Python-Dev
> <[email protected]> wrote:
>> Wild suggestion:
>>       Make None.__hash__ writable.
>> E.g.
>>       None.__hash__ = lambda : 0 # Currently raises AttributeError:
>> 'NoneType' object attribute '__hash__' is read-only
> Hashes have to be stable. If you change the hash of None after it's
> been inserted into a dictionary, you'll get all kinds of entertaining
> problems.
>
>>>> class X:
> ...     def __init__(self): self.hash = 0
> ...     def __hash__(self): return self.hash
> ...
>>>> x = X()
>>>> d = {x: "This is x"}
>>>> x.hash = 1
>>>> for key in d: print(key, key in d)
> ...
> <__main__.X object at 0x7f2d07c6f1c0> False
>
> ChrisA
> _______________________________________________
> Python-Dev mailing list -- [email protected]
> To unsubscribe send an email to [email protected]
> https://mail.python.org/mailman3/lists/python-dev.python.org/
> Message archived at https://mail.python.org/archives/list/[email protected]/message/OVVIKTG7CBN6BII4OBGIXWQJJXYCEO3I/
> Code of Conduct: http://python.org/psf/codeofconduct/

_______________________________________________
Python-Dev mailing list -- [email protected]
To unsubscribe send an email to [email protected]
https://mail.python.org/mailman3/lists/python-dev.python.org/
Message archived at https://mail.python.org/archives/list/[email protected]/message/L7JDJFPJKYNHIA7QVYGC74SYAVODM2IX/
Code of Conduct: http://python.org/psf/codeofconduct/