[Numpy-discussion] Ill-defined in-place operations (#1085)

[Charles R Harris]

On Wed, Apr 15, 2009 at 2:51 PM, Pauli Virtanen <pav at iki.fi> wrote:

> Wed, 15 Apr 2009 22:34:49 +0200, Matthieu Brucher wrote:
>
> > I think this is unavoidable. If we state clearly that every numpy
> > function assums non-pointer aliasing, then people have to care about
> > this themselves (like they would in Fortran, or in C++ for object-like
> > arrays).
>
> Nevertheless, this is an easy way to shoot yourself into foot. Also, (as
> indicated by the x.T example), it's doubtful anyone actually relies on
> the current behavior for N-D arrays, since it depends on order of data in
> memory, etc.
>
> It rather likely is possible to cheaply detect potentially troublesome
> cases and raise a warning. (The user can silence these, if the behavior
> is really relied on.) I don't know what is the performance impact of
> Python warnings, though.
>
> The alternative is to have really good documentation on views...
>

Asking the average user to understand memory issues is probably a bit much.
Better to raise a warning and let the sophisticated users override it if
they really need to. Checking if the same memory chunk is used should be
sufficient (I think that can be done).

Chuck
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