[Numpy-discussion] Polynomial silent breakage with 1.13

Eric Wieser wieser.eric+numpy at gmail.com
Fri Jul 7 13:14:25 EDT 2017


That’s a regression, and it’s on me, in 8762.

That was a side effect of a fix for the weird behaviour here
<https://github.com/numpy/numpy/pull/8762#issuecomment-286890002>.

I think we need to fix this in 1.13.2, so we should file an issue about it.

Eric
​

On Fri, 7 Jul 2017 at 18:31 Matthew Brett <matthew.brett at gmail.com> wrote:

> Hi,
>
> Our (nipy's) test suite just failed with the upgrade to numpy 1.13,
> and the cause boiled down to this:
>
> ```
> import numpy as np
>
> poly = np.poly1d([1])
> poly.c[0] *= 2
> print(poly.c)
> ```
>
> Numpy 1.12 gives (to me) expected output:
>
> [2]
>
> Numpy 1.13 gives (to me) unexpected output:
>
> [1]
>
> The problem is caused by the fact that the coefficients are now a
> *copy* of the actual coefficient array - I think in an attempt to stop
> us modifying the coefficients directly.
>
> I can't see any deprecation warnings with `-W always`.
>
> The pain point here is that code that used to give the right answer
> has now (I believe silently) switched to giving the wrong answer.
>
> Cheers,
>
> Matthew
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