On Wed, 17 Feb 2010 08:19:00 am David DiCato wrote:
I have a minor concern about certain corner cases with math.hypot and complex.__abs__, namely when one component is infinite and one is not a number. If we execute the following code:
import math inf = float('inf') nan = float('nan') print math.hypot(inf, nan) print abs(complex(nan, inf))
... then we see that 'inf' is printed in both cases. The standard library tests (for example, test_cmath.py:test_abs()) seem to test for this behavior as well, and FWIW, I personally agree with this convention.
What's the justification for that convention? It seems wrong to me. If you expand out hypot and substitute a=inf and b=nan, you get:
math.sqrt(inf*inf + nan*nan) nan
which agrees with my pencil-and-paper calculation: sqrt(inf*inf + nan*nan) = sqrt(inf + nan) = sqrt(nan) = nan -- Steven D'Aprano