On Sat, 02 Jun 2018 09:32:05 +0200, Peter J. Holzer wrote:
> Also nope. It looks like NaNs just mess up sorting in an unpredictable
> way. Is this the intended behaviour or just an accident of
> implementation? (I think it's the latter: I can see how a sort algorithm
> which doesn't treat NaN specially would produce such results.)
Neither -- it is a deliberate decision to ignore the possibility of such
pathological objects when sorting. Feature requests to reconsider this
decision in statistics.median will be considered seriously :-)
NANs are unordered values. ALL of these ought to return False, for ANY
float value x:
NAN < x
NAN <= x
NAN > x
NAN >= x
NAN == x
Regardless of the value of x, NAN <comparison> x is always false (apart
from != which is always true).
Python's sort algorithm assumes that objects have consistent, sensible
comparisons. If you write an object like this:
class Rubbish:
def __eq__(self, other):
return random.random() > 0.5
def __lt__(self, other):
return random.random() > 0.5
def __gt__(self, other):
return random.random() > 0.5
it too will mess up sorting in unpredictable ways. So don't do that.
--
Steven D'Aprano
"Ever since I learned about confirmation bias, I've been seeing
it everywhere." -- Jon Ronson
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