Seems to make sense to me? Or is the following a bug? >>> import numpy as np >>> u = np.zeros(5) >>> v = np.ones(5) >>> u array([0., 0., 0., 0., 0.]) >>> u[...] = v >>> u array([1., 1., 1., 1., 1.]) >>> v[4] = 5 >>> v array([1., 1., 1., 1., 5.]) >>> u array([1., 1., 1., 1., 1.])
If you don't do a copy, then it is a view, right? And so, should modifying v[4] change u[4]? Relatedly, if these were object arrays, of mutable objects, should mutating u[4] point to the exact same instance as v[4] and mutating it in one array means that the other array "sees" the same changes? Sorry if I'm missing the point, just want to make sure we don't inadvertently change important implicit behavior. Ben Root On Thu, Dec 26, 2024 at 7:07 AM Mateusz Sokol <mso...@quansight.com> wrote: > 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> >> > >> > _______________________________________________ >> > NumPy-Discussion mailing list -- >> > numpy-discussion@python.org<mailto:numpy-discussion@python.org> >> > To unsubscribe send an email to >> > numpy-discussion-le...@python.org<mailto: >> > numpy-discussion-le...@python.org> >> > https://mail.python.org/mailman3/lists/numpy-discussion.python.org/< >> > >> https://urldefense.com/v3/__https://mail.python.org/mailman3/lists/numpy-discussion.python.org/__;!!Bt8fGhp8LhKGRg!A_N5Cns4800odNjjStN3QAH94TwUNBEkvr7lqW4-PnnUiGS_kckVyXKfS4QTR4YADAXXGOTbKZ-6RDYTC7knRCMj$ >> > > >> > Member address: >> > stevenalonzoel...@gmail.com<mailto:stevenalonzoel...@gmail.com> >> > >> > _______________________________________________ >> > NumPy-Discussion mailing list -- numpy-discussion@python.org >> > To unsubscribe send an email to numpy-discussion-le...@python.org >> > https://mail.python.org/mailman3/lists/numpy-discussion.python.org/ >> > Member address: sebast...@sipsolutions.net >> >> _______________________________________________ >> NumPy-Discussion mailing list -- numpy-discussion@python.org >> To unsubscribe send an email to numpy-discussion-le...@python.org >> https://mail.python.org/mailman3/lists/numpy-discussion.python.org/ >> Member address: mso...@quansight.com >> > _______________________________________________ > NumPy-Discussion mailing list -- numpy-discussion@python.org > To unsubscribe send an email to numpy-discussion-le...@python.org > https://mail.python.org/mailman3/lists/numpy-discussion.python.org/ > Member address: ben.v.r...@gmail.com >
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