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

[Chris Barker]

Andrew,

I totally agree that it's not going to be that clear to folks -- but I'm as
stumped as you as to how to make it clear without getting really wordy.

Also, I think the percent error use case is infrequent, more likely would
be that a relative tolerance of 1e-8 means that the numbers are the same to
within about 8 significant decimal figures. After all, not many people
think in terms of 0.0000001%

Suggestions gladly accepted!

-Chris



On Thu, Jan 22, 2015 at 7:30 PM, Andrew Barnert <abarnert at yahoo.com> wrote:

> Overall I like it, but I'm not sure the help on the tol parameter is clear
> enough for people who don't already know what they want--in other words,
> the very people this function should be helping.
>
> In my experience, novices understand relative tolerance immediately if you
> put it in terms of "within X% of expected", but don't always understand it
> if you put it in terms of "within X * expected" or, worse, "relative to the
> magnitude of the expected value". Just using % in there somewhere makes
> people get the concept.
>
> Unfortunately, since the API doesn't actually use a percentage--and
> shouldn't--I'm not sure how to get this across in a one-liner in the help.
> You can always add something like "(e.g., a relative tolerance of .005
> means that the actual value must be within 0.5% of the expected value)",
> but that's way too verbose.
>
> (Also, I should note that the people I've explained this to have mostly
> been people with a US 1960-1990-style basic math education; I can't be sure
> that people who learned in another country, or in the post-post-new-math
> era in the US, etc. will respond the same way, although I do have a bit of
> anecdotal evidence from helping a few people on forums like StackOverflow
> that seems to imply they do.)
>
> Sent from a random iPhone
>
> On Jan 22, 2015, at 16:40, Chris Barker <chris.barker at noaa.gov> wrote:
>
> > is the relative tolerance -- it is the amount of error
> > allowed, relative to the magnitude of the expected value.
>



-- 

Christopher Barker, Ph.D.
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