[Numpy-discussion] PR for complex np.interp, question about assert_almost_equal

[Ralf Gommers]

On Tue, Dec 22, 2015 at 12:55 AM, Peter Creasey <
p.e.creasey.00 at googlemail.com> wrote:

> Hi all,
> I submitted a PR (#6872) for using complex numbers in np.lib.interp.
>
> The tests pass on my machine, but I see that the TravisCI builds are
> giving assertion fails (on my own test) with python 3.3 and 3.5 of the
> form:
> > assert_almost_equal
> > TypeError: Cannot cast array data from dtype('complex128') to
> dtype('float64') according to the rule 'safe'
>
> When I was writing the test I used np.testing.assert_almost_equal with
> complex128 as it works in my python 2.7, however having checked the
> docstring I cannot tell what the expected behaviour should be (complex
> or no complex allowed). Should my test be changed or the
> assert_almost_equal?
>

Hi Peter, that error is unrelated to assert_almost_equal. What happens is
that when you pass in a complex argument `fp` to your modified
`compiled_interp`, you're somewhere doing a cast that's not safe and
trigger the error at
https://github.com/numpy/numpy/blob/master/numpy/core/src/multiarray/ctors.c#L1930.
For what "safe casting" means, see
http://docs.scipy.org/doc/numpy/reference/generated/numpy.can_cast.html

Ralf
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