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

[Jaime Fernández del Río]

On Tue, Dec 22, 2015 at 7:42 AM, Ralf Gommers <ralf.gommers at gmail.com>
wrote:

>
>
> 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
>

The problem then is probably here
<https://github.com/numpy/numpy/pull/6872/files#diff-45aacfd88a495829ee10815c1d02326fL623>
.

You may want to throw in a PyErr_Clear()
<https://docs.python.org/3/c-api/exceptions.html#c.PyErr_Clear> when the
conversion of the fp array to NPY_DOUBLE fails before trying with
NPY_CDOUBLE, and check if it goes away.

Jaime

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