[Numpy-discussion] Boolean binary '-' operator

Stefan van der Walt stefanv at berkeley.edu
Sun Jun 25 12:45:38 EDT 2017

Hi Chuck

On Sun, Jun 25, 2017, at 09:32, Charles R Harris wrote:
> The boolean binary '-' operator was deprecated back in NumPy 1.9 and
> changed to an error in 1.13. This caused a number of failures in
> downstream projects. The choices now are to continue the deprecation
> for another couple of releases, or simply give up on the change. For
> booleans,  `a - b` was implemented as `a xor b`, which leads to the
> somewhat unexpected identity `a - b == b - a`, but it is a handy
> operator that allows simplification of some functions, `numpy.diff`
> among therm. At this point I'm inclined to give up on the deprecation
> and retain the old behavior. It is a bit impure but perhaps we can
> consider it a feature rather than a bug.
What was the original motivation behind the deprecation?  `xor` seems
like exactly what one would expect when subtracting boolean arrays.
But, in principle, I'm not against the deprecation (we've had to fix a
few problems that arose in skimage, but nothing big).

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