[Numpy-discussion] coercion rules for float32 in numpy are different from numarray

Travis Oliphant oliphant.travis at ieee.org
Fri Aug 25 07:50:32 CDT 2006

Sebastian Haase wrote:
>> This is now the behavior in SVN.   Note that this is different from both 
>> Numeric (which gave an error) and numarray (which coerced to float32). 
>> But, it is consistent with how mixed-types are handled in calculations 
>> and is thus an easier rule to explain.
>> Thanks for the testing.
>> -Travis
> How hard would it be to change the rules back to the numarray behavior ?
It wouldn't be hard, but I'm not so sure that's a good idea.   I do see 
the logic behind that approach and it is worthy of some discussion.   
I'll give my current opinion:

The reason I changed the behavior is to get consistency so there is one 
set of rules on mixed-type interaction to explain. You can always do 
what you want by force-casting your int32 arrays to float32.    There 
will always be some people who don't like whichever behavior is 
selected, but we are trying to move NumPy in a direction of consistency 
with fewer exceptions to explain (although this is a guideline and not 
an absolute requirement).

Mixed-type interaction is always somewhat ambiguous.  Now there is a 
consistent rule for both universal functions and other functions (move 
to a precision where both can be safely cast to --- unless one is a 
scalar and then its precision is ignored).

If you don't want that to happen, then be clear about what data-type 
should be used by casting yourself.   In this case, we should probably 
not try and guess about what users really want in mixed data-type 


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