[Python-ideas] PEP 485: A Function for testing approximate equality

[Chris Barker]

On Mon, Jan 26, 2015 at 10:31 AM, Antoine Pitrou <solipsis at pitrou.net>
wrote:

> > But throughout all this -- I haven't thought of a single case where I
> would
> > prefer a symmetric test and it would matter.
>
> But then it begs the question: are there cases where an asymmetric test
> matters?


Yes -- see the example in the PEP and on this list. If you have a known
value, and you want to know whether the value at hand is within some error
of the known value, then you want an asymmetric test -- and if you have
errors on order of 10% -- it does make a difference. Granted, I don't
expect this use case to be common, but it was brought up on this list.


> Simplicity has its virtues.


But which is more simple? I came to the conclusion that the asymmetric was
simpler to explain and reason about in any case.

-Chris


-- 

Christopher Barker, Ph.D.
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