Rich Comparisons Gotcha

[Robert Kern]

Rasmus Fogh wrote:

> Current behaviour is both inconsistent and counterintuitive, as these
> examples show.
> 
>>>> x = float('NaN')
>>>> x == x
> False

Blame IEEE for that one. Rich comparisons have nothing to do with that one.

>>>> ll = [x]
>>>> x in ll
> True
>>>> x == ll[0]
> False
> 
>>>> import numpy
>>>> y = numpy.zeros((3,))
>>>> y
> array([ 0.,  0.,  0.])
>>>> bool(y==y)
> Traceback (most recent call last):
>   File "<stdin>", line 1, in <module>
> ValueError: The truth value of an array with more than one element is
> ambiguous. Use a.any() or a.all()
>>>> ll1 = [y,1]
>>>> y in ll1
> True
>>>> ll2 = [1,y]
>>>> y in ll2
> Traceback (most recent call last):
>   File "<stdin>", line 1, in <module>
> ValueError: The truth value of an array with more than one element is
> ambiguous. Use a.any() or a.all()
> 
> Can anybody see a way this could be fixed (please)? I may well have to
> live with it, but I would really prefer not to.

Make a concrete proposal for fixing it that does not break backwards compatibility.

-- 
Robert Kern

"I have come to believe that the whole world is an enigma, a harmless enigma
  that is made terrible by our own mad attempt to interpret it as though it had
  an underlying truth."
   -- Umberto Eco