[Numpy-discussion] type coercion question

Rick White rlw at stsci.edu
Wed Mar 31 09:55:36 CST 2004


On Wed, 31 Mar 2004, Perry Greenfield wrote:

> Just to summarize what I see as acceptable choices:
>
> 1) ints promote to Float32 (current behavior)
> 2) ints promote to Float64
> 3) Int32 promotes to Float64, lesser ints promote to Float32 (Numeric
> behavior)

I'm also +1 on option (2).

I believe that this will not cause problems with unwanted promotions.  The
result of cos(1) is a scalar Python float, regardless of whether 1 is
converted to a Float32 or a Float64 before the cosine is evaluated.  Then
if that scalar is used with a Float32 numarray, it gets converted to a
Float32 and the result is Float32.  For example:

   >>> from numarray import *
   >>> cos(1)*ones(1,Float32)
   array([ 0.54030228], type=Float32)
   >>> cos(1.0)*ones(1,Float32)
   array([ 0.54030228], type=Float32)

So it seems to me there is no downside to converting integers to Float64
when the ufunc requires a float.  And I find it hard to believe that any
Numeric users are counting on behavior (3).
				Rick





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