[Numpy-discussion] __array_wrap__

[Charles R Harris]

On Tue, Sep 29, 2009 at 1:12 PM, Robert Kern <robert.kern at gmail.com> wrote:

> On Tue, Sep 29, 2009 at 14:08, Charles R Harris
> <charlesr.harris at gmail.com> wrote:
> >
> >
> > On Tue, Sep 29, 2009 at 12:48 PM, Robert Kern <robert.kern at gmail.com>
> wrote:
> >>
> >> On Tue, Sep 29, 2009 at 13:35, Charles R Harris
> >> <charlesr.harris at gmail.com> wrote:
> >> >
> >> > On Tue, Sep 29, 2009 at 12:23 PM, Robert Kern <robert.kern at gmail.com>
> >> > wrote:
> >> >>
> >> >> On Tue, Sep 29, 2009 at 13:09, Charles R Harris
> >> >> <charlesr.harris at gmail.com> wrote:
> >> >> >
> >> >> >
> >> >> > On Tue, Sep 29, 2009 at 11:00 AM, Neal Becker <ndbecker2 at gmail.com
> >
> >> >> > wrote:
> >> >> >>
> >> >> >> fixed_pt arrays need to apply the overflow_policy after operations
> >> >> >> (overflow_policy could be clip, or throw exception).
> >> >> >>
> >> >> >> I thought __array_wrap__ would work for this, but it seems to not
> be
> >> >> >> called
> >> >> >> when I need it.  For example:
> >> >> >>
> >> >> >> In [13]: obj
> >> >> >> Out[13]: fixed_pt_array([  0,  32,  64,  96, 128])
> >> >> >>
> >> >> >> In [14]: obj*100 < this should overflow
> >> >> >> enter: [  0  32  64  96 128] << on entry into __array_wrap
> >> >> >> enter: [0 32 64 96 128]
> >> >> >> exit: [  0  32  64  96 128]
> >> >> >> Out[14]: fixed_pt_array([    0,  3200,  6400,  9600, 12800])
> >> >> >>
> >> >> >> Apparantly, obj*100 is never passed to array_wrap.
> >> >> >>
> >> >> >> Is there another way I can do this?
> >> >> >>
> >> >> > I believe array wrap has to be explicitly called after the fact.
> >> >>
> >> >> Ufuncs call __array_wrap__ implicitly.
> >> >>
> >> >
> >> > Thanks for the info. How do they decide which one to call?
> >>
> >> The .__array_priority__ attribute.
> >
> > What if they are the same?
>
>
> http://docs.scipy.org/doc/numpy/user/c-info.beyond-basics.html?highlight=__array_priority__#ndarray.__array_priority__
>
>
And that is why it is a bad idea.

Chuck
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