It looks like general assignment function `array_assign_subscript` calls
`PyArray_CopyObject(view, op)` link
<https://github.com/numpy/numpy/blob/a07c6c5f12eec1322d2487f0ed935c5c13b8d883/numpy/_core/src/multiarray/mapping.c#L1938>
which in turn always calls `PyArray_DiscoverDTypeAndShape` with `copy=1`
and this is where `copy=True` takes place.
We could add a `copy` parameter to `PyArray_CopyObject` or set `copy=-1`
(to `None`) for the `PyArray_DiscoverDTypeAndShape` call.
Mateusz
On Thu, Dec 26, 2024 at 10:19 AM Sebastian Berg <sebast...@sipsolutions.net>
wrote:
> That seems like a bug but not sure why it would happen. It needs to
> call `__array__`, but indeed of course not with `copy=True`.
>
> Would you open an issue on github?
>
> - Sebastian
>
>
> On Thu, 2024-12-26 at 03:46 +0000, Israel, Daniel M via NumPy-
> Discussion wrote:
> > Sure. I didn’t originally, because I thought it would require an
> > entire custom array container, but the following trivial example
> > actually shows the behavior in question:
> >
> > import numpy
> >
> > class MyThing(object):
> > def __array__(self, dtype=None, copy=None):
> > print(f"MyThing.__array__(dtype={dtype}, copy={copy})")
> > return numpy.ones((5, 5))
> >
> > u = numpy.zeros((5, 5))
> > v = MyThing()
> >
> > u[...] = v
> >
> > If you run this code, as part of the final assignment statement, the
> > __array__ method is called for ‘v’ with copy=True. Why?
> >
> > —
> > Daniel Israel
> > XCP-4: Continuum Models and Numerical Algorithms
> > d...@lanl.gov
> >
> > On Dec 25, 2024, at 3:23 PM, Steven Ellis
> > <stevenalonzoel...@gmail.com> wrote:
> >
> > Hi David,
> >
> > New to the listserv, but, maybe you can provide a reproducible
> > example?
> >
> > Steven
> >
> > On Wed, Dec 25, 2024, 2:19 PM Israel, Daniel M via NumPy-Discussion
> > <numpy-discussion@python.org<mailto:numpy-discussion@python.org>>
> > wrote:
> > I was updating some code that uses a custom array container built
> > with the mixin library. Specifically, I was trying to eliminate some
> > warnings due to the change to the __array__ interface to add a copy
> > argument. In doing so, I discovered that, for two objects u, v in my
> > container class, the code:
> >
> > u[…] = v
> >
> > performs a copy on v. Specifically, it calls __array__() with
> > copy=True. This seems unnecessary and wasteful of memory. Can
> > someone explain to me what is happening here?
> >
> > Thanks.
> >
> > —
> > Daniel Israel
> > XCP-4: Continuum Models and Numerical Algorithms
> > d...@lanl.gov<mailto:d...@lanl.gov>
> >
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