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

Chris Barker chris.barker at noaa.gov
Wed Jan 28 00:00:27 CET 2015


On Tue, Jan 27, 2015 at 2:35 PM, Guido van Rossum <guido at python.org> wrote:

> I'm still confused. We're talking about a function that compares two
> simple values, right? Where does the sequence of values come from?
>

it comes from wherever, but the idea is that the function itself is called
in a loop or comprehension, we could require something like:

[ is_close_to(i) for i in seq if abs(i) > abs_tol else abs(i) <= abs_tol]

but I prefer:

[ is_close_to(i, abs_tolerance=abs_tol) for i in seq ]

And it gets worse for the TestCase.assert** - those are designed to act on
a sequence, so you would need to specify both your relative tolerance and
absolute tolerance anyway, if your sequence might have zeros in it.


>  Or perhaps you're talking about assertApproxEqual in test_statistics.py?
> That has so many ways to specify the relative and absolute tolerance that I
> give up understanding it.
>

Something like that, yes, but with a cleaner API and better docs ;-)

-Chris


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Christopher Barker, Ph.D.
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