Test None for an object that does not implement ==

[Devin Jeanpierre]

> At first glance this looked like it should be a simple boolean "and", but
> then I realized that when a and c are both unequal to None, the result would
> also be True.  This implies the logical approach would be exclusive-or (^).

Among booleans, "!=" is exclusive or and "==" is its negation. I don't
see the point of complicating the formula to use ^.

(related: <= is implication. Which is sad, because the arrow points
the wrong way!)

The issue here is that "== None" is being used instead of "is None",
but I believe that's been covered. Your response doesn't include it,
so maybe it's worth restating.

-- Devin

On Sun, Dec 25, 2011 at 6:45 PM, Larry Hudson <orgnut at yahoo.com> wrote:
> On 12/24/2011 11:09 PM, GZ wrote:
>>
>> Hi,
>>
>> I run into a weird problem. I have a piece of code that looks like the
>> following:
>>
>> f(...., a=None, c=None):
>>     assert  (a==None)==(c==None)
>>
> <...>
>
> At first glance this looked like it should be a simple boolean "and", but
> then I realized that when a and c are both unequal to None, the result would
> also be True.  This implies the logical approach would be exclusive-or (^).
>  Try this expression:
>
>     not ((a==None) ^ (c==None))
>
> OTOH, if what you really want is simply to check that both are None (my
> first impression), then it's simply:
>
>     (a==None) and (c==None)
>
> Most of the replies you're getting here seem unnecessarily complicated.
>
>> Thanks,
>> gz
>
>
>    -=- Larry -=-
> --
> http://mail.python.org/mailman/listinfo/python-list