[Numpy-discussion] numpy vs algebra Was: Integers to negative integer powers...

[Stephan Hoyer]

On Tue, Jan 3, 2017 at 9:00 AM, Yaroslav Halchenko <lists at onerussian.com>
wrote:

> Sorry for coming too late to the discussion and after PR "addressing"
> the issue by issuing an error was merged [1].  I got burnt by new
> behavior while trying to build fresh pandas release on Debian (we are
> freezing for release way too soon ;) ) -- some pandas tests failed since
> they rely on previous non-erroring behavior and we got  numpy 1.12.0~b1
> which included [1] in unstable/testing (candidate release) now.
>
> I quickly glanced over the discussion but I guess I have missed
> actual description of the problem being fixed here...  what was it??
>
> previous behavior, int**int->int made sense to me as it seemed to be
> consistent with casting Python's pow result to int, somewhat fulfilling
> desired promise for in-place operations and being inline with built-in
> pow results as far as I see it (up to casting).


I believe this is exactly the behavior we preserved. Rather, we turned some
cases that previously often gave wrong results (involving negative integer
powers) into errors.

The pandas test suite triggered this behavior, but not intentionally, and
should be fixed in the next release:
https://github.com/pandas-dev/pandas/pull/14498
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