[Numpy-discussion] round / set_printoptions discrepancy
hodge at stsci.edu
Fri Sep 13 08:59:17 EDT 2019
On 9/13/19 8:45 AM, Irvin Probst wrote:
> On 13/09/2019 14:05, Philip Hodge wrote:
>> Isn't that just for consistency with Python 3 round()? I agree that
>> the discrepancy with np.set_printoptions is not necessarily expected,
>> except possibly for backwards compatibility.
> I've just checked and np.set_printoptions behaves as python's round:
> >>> round(16.055,2)
> >>> np.round(16.055,2)
> I don't know why round and np.round do not behave the same, actually I
> would even dare to say that I don't care :-)
> However np.round and np.set_printoptions should provide the same
> output, shouldn't they ? This discrepancy is really disturbing whereas
> consistency with python's round looks like the icing on the cake but
> in no way a required feature.
Python round() is supposed to round to the nearest even value, if the
two closest values are equally close. So round(16.055, 2) returning
16.05 was a surprise to me. I checked the documentation and found a
note that explained that this was because "most decimal fractions can't
be represented exactly as a float." round(16.55) returns 16.6.
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