[Numpy-discussion] rank-0 arrays are mutable scalars
huaiyu_zhu at yahoo.com
Wed Sep 18 00:03:02 CDT 2002
On Tue, 17 Sep 2002, Travis Oliphant wrote:
> > len(d) == Exception == d.shape
> > # Currently the last is wrong?
> Agreed, but this is because d is an integer and out of Numerics control.
> This is a case for returning 0d arrays rather than Python scalars.
That is one problem. It can be removed by using shape(d).
More fundamentally, though, len(d) == shape(d) == () => IndexError.
I think Konrad made this point a few days back.
> > size(d) == 1 == product(d.shape)
> > # Currently the last is wrong
> I disagree that this is wrong. This works as described for me.
Right. Change d.shape to shape(d) here (and in several other places).
> Why is this? I thought you argued the other way for len(scalar). Of
> course, one solution is that we could overwrite the len() function and
> allow it to work for scalars.
Raising exception is the correct behavior, not a problem to be solved.
> > Conclusion 5: rank-0 int arrays should be allowed to act as indices.
> > See property 5.
> Can't do this for lists and other builtin sequences.
If numarray defines a consistent set of behaviors for integer types that
is intuitively understandable, it might not be difficult to persuade core
Python to check against an abstract integer type.
> > - Is there substantial difference in overhead between rank-0 arrays and
> > scalars?
That would be one major problem.
However, after giving this some more thoughts, I'm starting to doubt the
analogy I made. The problem is that in the end there is still a need to
index an array and obtain a good old immutable scalar. So
- What notation should be used for this purpose? We can use c to get
immutable scalars and c[0,] for rank-0 arrays / mutable scalars. But
what about other ranks? Python does not allow distinctions based on
a[1,1,1] versus a[(1,1,1)] or d versus d[()].
- This weakens the argument that rank-0 arrays are scalars, since that
argument is essentially based on sum(c) and c being of the same type.
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