[Numpy-discussion] What is the logical value of nan?

Charles R Harris charlesr.harris@gmail....
Tue Mar 10 17:35:51 CDT 2009


On Tue, Mar 10, 2009 at 4:19 PM, Timothy Hochberg <tim.hochberg@ieee.org>wrote:

>
>
> On Tue, Mar 10, 2009 at 2:49 PM, Charles R Harris <
> charlesr.harris@gmail.com> wrote:
>
>>
>>
>> On Tue, Mar 10, 2009 at 3:16 PM, Stéfan van der Walt <stefan@sun.ac.za>wrote:
>>
>>> 2009/3/10 Pauli Virtanen <pav@iki.fi>:
>>> > Nonzero Python object, hence True. Moreover, it's also True in Python:
>>>
>>> Also in C:
>>>
>>> #include <math.h>
>>> #include <stdio.h>
>>>
>>> int main() {
>>>    double nan = sqrt(-1);
>>>    printf("%f\n", nan);
>>>    printf("%i\n", bool(nan));
>>>    return 0;
>>> }
>>>
>>> $ ./nan
>>> nan
>>> 1
>>>
>>
>> So resolved, it is True.
>>
>
> I appear to be late to the party, but IMO it should raise an exception in
> those cases where it's feasible to do so.
>
>
That also seems reasonable to me. There is also the unresolved issue of
whether casting nan to an integer should raise an exception, currently it is
just converted to 0.

Chuck
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