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From: Ben Finney <ben+python@benfinney.id.au>
Subject: Re: Is nan in (nan,) correct?
Date: Fri, 06 Mar 2015 10:39:59 +1100
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Xref: csiph.com comp.lang.python:86967

sohcahtoa82@gmail.com writes:

> On Thursday, March 5, 2015 at 3:20:16 PM UTC-8, Ben Finney wrote:
> > It is fine to define such a type in Python, because 'is' does not
> > necessarily imply '=='.
>
> Do you have an example of where `a is b` but `a != b` in Python?

Maybe I misunderstand your question, but you've already been discussing
such an example. Here it is for clarity::

    >>> nan = float("NaN")
    >>> (nan is nan) == (nan == nan)
    False
    >>> nan is nan
    True
    >>> nan == nan
    False

> `None == None` is True.

Right, the Python `None` is not the null I was describing. Python does
allow for a null with the semantics I described, because ‘is’ does not
imply ‘==’.

-- 
 \      “We suffer primarily not from our vices or our weaknesses, but |
  `\    from our illusions.” —Daniel J. Boorstin, historian, 1914–2004 |
_o__)                                                                  |
Ben Finney