[Numpy-discussion] How to trigger warnings for integer division in python 2

Sebastian Berg sebastian at sipsolutions.net
Fri Aug 19 13:03:15 EDT 2016

On Fr, 2016-08-19 at 11:29 -0400, Stuart Berg wrote:
> Hi,
> To help people migrate their code bases from Python 2 to Python 3,
> the python interpreter has a handy option '-3' that issues warnings
> at runtime.  One of the warnings is for integer division:
> $ echo "print 3/2" > /tmp/foo.py
> $ python -3 /tmp/foo.py
> /tmp/foo.py:1: DeprecationWarning: classic int division
>   print 3/2
> 1
> But no warnings are shown for division of numpy arrays, e.g. for a
> statement like this:
> print np.array([3]) / np.array([2])
> I see that np.seterr can be used to issue certain types of division
> warnings, but not this one.  Is there a way to activate integer
> division warnings?  It would really help me migrate my application to
> Python 3.

I don't think numpy implements any py3kwarnings. It seems that it would
be possible though. On newer versions we got more strict about using
floats instead of ints, so some of these places might follow up with a
warning quickly.
I guess the question is whether we should aim to add at least some of these warnings and someone is willing to put in the effort (I suppose it is likely only a few places). I am not sure how easy they are on the C side, but probably not difficult at all.

- Sebastian

> Thanks,
> Stuart
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