[Python-Dev] Optional delta argument for assertAlmostEqual

[Charles McCreary]

A good summary on floating point comparison algorithms can be found at

http://www.boost.org/doc/libs/1_34_0/libs/test/doc/components/test_tools/floating_point_comparison.html

I, too, redefine almostEquals so that the comparison is more robust

+1

On Sun, Mar 28, 2010 at 2:06 AM, Steven D'Aprano <steve at pearwood.info>wrote:

> On Sun, 28 Mar 2010 02:54:19 pm Charles McCreary wrote:
> > Perhaps not just absolute but relative tolerance, e.g.:
> >
> > def isclose(x, y, rtol=1.e-5, atol=1.e-8):
> >     return abs(x-y) <= atol + rtol * abs(y)
>
> I'm not sure why you add the tolerances like that. Surely a more
> appropriate approach is to compare the values against the tolerances
> individually, and return True if they meet either condition.
>
> For what it's worth, here's a recipe I wrote for approximately equal,
> following someone's complaint on comp.lang.python that Python has no
> approximately-equal operator.
>
> http://code.activestate.com/recipes/577124-approximately-equal/
>
> Comments and criticism welcome.
>
> I've never found unittest.TestCase.assertAlmostEqual to be useful. I
> generally write my own comparison function, then call:
>
> assert_(compare(x, y))
>
> as needed. I'm +0.5 on Michael's suggested change -- it will make
> assertAlmostEqual marginally more useful, which is a plus, but I'm not
> sure that absolute tolerances are better than relative. But how general
> do we want to be? "Almost equal" means something different to everyone.
>
>
>
> > On Fri, Mar 26, 2010 at 7:59 PM, Michael Foord
> <fuzzyman at voidspace.org.uk>wrote:
> > > Hello all,
> > >
> > > A user has suggested an optional argument to
> > > unittest.TestCase.assertAlmostEqual for specifying a maximum
> > > difference between the expected and actual values, instead of using
> > > rounding.
> [snip]
>
>
>
> --
> Steven D'Aprano
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-- 
Charles McCreary P.E.
CRM Engineering
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