Wait, when assignments and slicing mix wasn't the behavior supposed to be equivalent to copying the RHS to a temporary and then assigning using the temporary. Is that a false memory ? Or has the behavior changed ? As long as the behavior is well defined and succinct it should be ok
On Tuesday, July 28, 2015, Sebastian Berg <sebast...@sipsolutions.net> wrote: > > On Mon Jul 27 22:51:52 2015 GMT+0200, Sturla Molden wrote: > > On 27/07/15 22:10, Anton Akhmerov wrote: > > > Hi everyone, > > > > > > I have encountered an initially rather confusing problem in a piece of > > > code that attempted to symmetrize a matrix: `h += h.T` > > > The problem of course appears due to `h.T` being a view of `h`, and > > > some elements being overwritten during the __iadd__ call. > > > > I think the typical proposal is to raise a warning. Note there is > np.may_share_memoty. But the logic to give the warning is possibly not > quite easy, since this is ok to use sometimes. If someone figures it out > (mostly) I would be very happy zo see such warnings. > > > > Here is another example > > > > >>> a = np.ones(10) > > >>> a[1:] += a[:-1] > > >>> a > > array([ 1., 2., 3., 2., 3., 2., 3., 2., 3., 2.]) > > > > I am not sure I totally dislike this behavior. If it could be made > > constent it could be used to vectorize recursive algorithms. In the case > > above I would prefer the output to be: > > > > array([ 1., 2., 3., 4., 5., 6., 7., 8., 9., 10.]) > > > > It does not happen because we do not enforce that the result of one > > operation is stored before the next two operands are read. The only way > > to speed up recursive equations today is to use compiled code. > > > > > > Sturla > > > > > > _______________________________________________ > > NumPy-Discussion mailing list > > NumPy-Discussion@scipy.org <javascript:;> > > http://mail.scipy.org/mailman/listinfo/numpy-discussion > > > > > _______________________________________________ > NumPy-Discussion mailing list > NumPy-Discussion@scipy.org <javascript:;> > http://mail.scipy.org/mailman/listinfo/numpy-discussion >
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