NoneType and new instances

Steven D'Aprano steve+comp.lang.python at
Sun Jul 31 06:28:57 CEST 2011

Terry Reedy wrote:

> On 7/30/2011 12:39 PM, bruno.desthuilliers at wrote:
>> On 28 juil, 17:39, Ethan Furman<et... at>  wrote:
>>> -->  bool(0) is bool(0)
>>> True
>> This test is not reliable
> It is in the sense that it will always work -- because False/True are
> doubletone constants and so documented.

Surely that should be doubleton :)

2.2: True and False released as names for 1 and 0; bool was a built-in
function, but not a type.

2.3: bool promoted to a type; True and False actual bools. The documentation
claims that there's only one instance of each.

I'm sure that I remember a short period during which Python had bools, but
didn't guarantee that there would only be one instance of True and one of
False, but I'm damned if I can find any evidence of this. Am I


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