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

Chris Barker chris.barker at noaa.gov
Sat Jan 24 05:21:29 CET 2015

On Fri, Jan 23, 2015 at 6:41 PM, Chris Angelico <rosuav at gmail.com> wrote:

> On Sat, Jan 24, 2015 at 1:35 PM, Andrew Barnert
> <abarnert at yahoo.com.dmarc.invalid> wrote:
> > Maybe the answer there is to have an is_close_to_0 function, instead of
> a parameter that's only useful if expected is 0? But then you might have,
> say, a comprehension where some of the expected values are 0 and some
> aren't, so maybe not...
> >
> That's a more philosophical question about API design. It's probably
> worth mentioning the two options in the PEP - separate function for
> "close to zero" with these args, or put it all into the one function
> with those args.

I could mention it -- though I started all this thinking that we should
keep relative and absolute tolerance separate, then realized that relative
was going to be useless for zero, so added the absolute tolerance to cover
that (which I originally named zero_tol, but realized that it really was
absolute everywhere...). Now that we're thinking that we can have a switch
for the exactly zero case, then there may be no need to have an absoute
tolerance parameter, but only relative and zero.

Then you'd have a separate function (if you wanted) for absolute tolerance,
so it could have a default -- that may be better than requiring the user to
set the parameter to get an absolute tolerance test at all.

I guess the key question is if someone would want both an relative
tolerance and an absolute tolerance, aside from the zero issue.


> ChrisA
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Christopher Barker, Ph.D.

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