[Numpy-discussion] should rint return int?

Robert Kern robert.kern at gmail.com
Mon Apr 28 15:21:59 EDT 2014

On Mon, Apr 28, 2014 at 6:36 PM, Neal Becker <ndbecker2 at gmail.com> wrote:
> I notice rint returns float.  Shouldn't it return int?
> Would be useful when float is no longer acceptable as an index.  I think
> conversion to an index using rint is a common idiom.

C's rint() does not:


This is because there are many integers that are representable as
floats/doubles/long doubles that are well outside of the range of any
C integer type, e.g. 1e20.

Python 3's round() can return a Python int because Python ints are
unbounded. Ours aren't.

That said, typically the first thing anyone does with the result of
rounding is to coerce it to a native int dtype without any checking.
It would not be terrible to have a function that rounds, then coerces
to int but checks for overflow and passes that through the numpy error
mechanism to be controlled. But it shouldn't be called rint(), which
is intended to be as thin a wrapper over the C function as possible.

Robert Kern

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