[Numpy-discussion] Possible bug in scalar * array

Todd Miller jmiller at stsci.edu
Tue Oct 21 07:34:02 EDT 2003

On Tue, 2003-10-21 at 03:53, Francesc Alted wrote:
> A Dilluns 20 Octubre 2003 21:36, Todd Miller va escriure:
> > I talked this over with Perry and we concluded that it's probably a good
> > thing to trap the out of range scalar values before using them.  Thus,
> > we're proposing to fix the error handling,  but to make the calls in
> > question raise an overflow exception on the first call.  We are
> > interested in hearing other opinions however.  Comments?
> You mean implementing range checking in numarray objects? In my opinion,
> that would be a very nice feature, although I don't know how that would
> affect the assignment performance.

I don't anticipate any impact on performance for the limited scope we
were proposing:  overflow checking for the scalar parameters of binary
ufuncs.  There are other areas where overflow checking could be employed
but won't be.  So, trying to create a more coherent picture,

Here is where we will check for overflows:

1. fromlist(), if you specify check_overflow=1.  
2. scalar parameters of binary ufuncs.  So 1+a will make sure "1" fits
in the array implied by a.type().
3. non-array-sequence parameters of binary ufuncs.  So add(a,[1,2,3])
ensures that [1,2,3] can be stored in an array of the type implied by
array a. 
4. The multiply ufunc.
5. a[<single_element_index>] = x  whenever a._check_overflow is 1.

Here is where we won't check for overflows:

1. array(), or fromlist() by default.
2. most binary ufuncs.  So a+b won't check, assuming a and b are both
3. a[<block_of_elements_index>] = b, regardless of a._check_overflow.

Comments?  Anything grossly inconsistent here?

> -- 
> Francesc Alted
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Todd Miller 			
Space Telescope Science Institute
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