Probably this will cause a lot of groans, but I've definitely written code modifying `broadcast_to` outputs, intentionally. As such I am -1 on this whole endeavour. My preference on making arrays read-only is to have a very light touch if any. As an example, at some point `np.diag` started returning read-only views. Setting or modifying the diagonal of a matrix is a common operation, so this decision uglified my code (grab the diagonal, make it writeable, write to it, instead of `np.diag(M) = x`.
I'll admit that the times that I modified the `broadcast_to` output I felt rather hacky and sheepish, but the point is that it's unlikely that someone who is using this function doesn't know what they're doing, isn't it? I wouldn't have even thought to look for this function before I understood what broadcasting and 0-strides were. In fact, I use it *specifically* to save memory and use zero strides. Matti, could you comment a bit on the motivation behind this change and why you feel it's necessary? Thanks, Juan. > On 25 Dec 2018, at 10:26 pm, Hameer Abbasi <einstein.edi...@gmail.com> wrote: > > Hi! > > Broadcasting almost always returns a repeated output > (except when all arrays are the same shape), that’s the entire point. I > suspect this function is in fairly widespread use and will therefore cause a > lot of downstream issues when repeating, so I’m -0.5 on a DeprecationWarning. > A FutureWarning might be more appropriate, in which case I’m +0.2. > > As for making the output read-only, that might break code, but most likely > the code was erroneous anyway. But breaking backward-compatibility without a > grace period is unheard of in this community. I’m +0.5 on it anyway. 🤷🏻♂️ > > Overall, a kind of hairy problem with no clear solution. > > Best Regards, > Hameer Abbasi > > On Tuesday, Dec 25, 2018 at 12:13 PM, Matti Picus <matti.pi...@gmail.com > <mailto:matti.pi...@gmail.com>> wrote: > In PR 12609 https://github.com/numpy/numpy/pull/12609 I added code to > emit a DepricationWarning when broadcast_arrays returns an array where > the output is repeated. While this is a minimal fix to the problem, > perhaps we should consider making the output readonly immediately instead? > > > - A deprecation cycle requires two changes to downstream user's code: > one to filter the deprecation warning, and another when we actually make > the change > > - Writing to the repeated data will cause errors now. > > > What do you think, should we change the behaviour at all, and if so > should we depricate it over two releases or change it immediately? > > > The original issue is here https://github.com/numpy/numpy/issues/2705 > > > Matti > > _______________________________________________ > NumPy-Discussion mailing list > NumPy-Discussion@python.org > https://mail.python.org/mailman/listinfo/numpy-discussion > > _______________________________________________ > NumPy-Discussion mailing list > NumPy-Discussion@python.org > https://mail.python.org/mailman/listinfo/numpy-discussion
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