[Numpy-discussion] Scalar coercion

Charles R Harris charlesr.harris@gmail....
Thu Mar 1 18:39:49 CST 2007


On 3/1/07, Travis Oliphant <oliphant@ee.byu.edu> wrote:
>
>
> A ticket was posted that emphasizes that the current behavior of NumPy
> with regards to scalar coercion is different than numarray's behavior.
> If we were pre 1.0, I would probably change the behavior to be in-line
> with numarray.  But, now I think it needs some discussion because we are
> changing the behavior of a released version of NumPy and we need some
> more conservatism in how changes happen.
>
> If we can classify the current behavior as a bug then we can change it.
> Otherwise, I'm concerned.
>
> The behavior has to do with a mixed scalar/array computation.   NumPy
> does not let scalars (equivalently 0-d arrays) determine the output type
> of the array operation, *unless* the scalar is of a fundamentally
> different kind (i.e. the array is an integer-type but the scalar is a
> floating-point type).  In this case, the current behavior is to coerce
> the array to the smallest-type in that general category of scalars.
>
> The reason for this behavior is to make sure that
>
> array([1,2,3,4],int8)*10  returns an int8  (instead of an int32 because
> of how the 10 is interpreted by Python).
>
> The current behavior, however, also means that
>
> array([1,2,3,4],int8)*10.0  will return a float32 array.
>
>
> I think numarray would return a float64 array in this case (i.e. the
> type of the scalar would be honored when the coercion was between two
> different kinds of arrays).


I feel that the default types should be integer, float64, cfloat64, with the
other types for designer apps with special needs. However

array([1,2,3,4],int8)*float32(10.0)

Should coerce to float32, not float64, because whoever wrote it took the
trouble to be specific about the type for a reason. So I agree with the
change you propose and I doubt it will be noticed except by those who find
numpy behaving as they expect.

Chuck
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