[Numpy-discussion] checking for array type in C extension

Robert Kern robert.kern@gmail....
Fri Jun 18 09:52:30 CDT 2010


On Fri, Jun 18, 2010 at 09:43, Berthold Hoellmann
<berthold.hoellmann@gl-group.com> wrote:
> Pauli Virtanen <pav@iki.fi> writes:
>
>> pe, 2010-06-18 kello 12:49 +0200, Berthold Hoellmann kirjoitti:
>> [clip]
>>> tst.inttestfunc(np.array((1,2),dtype=np.int))
>>> tst.inttestfunc(np.array((1,2),dtype=np.int8))
>>> tst.inttestfunc(np.array((1,2),dtype=np.int16))
>>> tst.inttestfunc(np.array((1,2),dtype=np.int32))
>>> tst.inttestfunc(np.array((1,2),dtype=np.int64))
>>>
>>> hoel@pc090498 ~/pytest $ PYTHONPATH=build/lib.win32-2.5/ python xx.py
>>> 1.4.1 ['C:\\Python25\\lib\\site-packages\\numpy']
>>> PyArray_TYPE(array): 7; NPY_INT: 5
>>> NPY_INT not found
>>> PyArray_TYPE(array): 1; NPY_INT: 5
>>> NPY_INT not found
>>> PyArray_TYPE(array): 3; NPY_INT: 5
>>> NPY_INT not found
>>> PyArray_TYPE(array): 7; NPY_INT: 5
>>> NPY_INT not found
>>> PyArray_TYPE(array): 9; NPY_INT: 5
>>> NPY_INT not found
>>>
>>> NPY_INT32 is 7, but shouldn't NPY_INT correspond to numpy.int. And what
>>> kind of int is NPY_INT in this case?
>>
>> I think the explanation is the following:
>>
>> - NPY_INT is a virtual type that is either int32 or int64, depending on
>>   the native platform size.
>>
>> - It has its own type code, distinct from NPY_SHORT (= 3 = int32) and
>>   NPY_LONG (= 7 = int64).
>>
>> - But the type specifier is replaced either by NPY_SHORT or NPY_LONG
>>   on array creation, so no array is of this dtype.
>>
>>       Pauli
>
> The documentation (i refere to NumPy User Guide, Release 1.5.0.dev8106)
> claims that numpy.int is platform int and that "NPY_INT" is a C based
> name, thus referring to int also.

It is referring to the Python int type, not the C int type. Python
ints are actually C longs underneath.

-- 
Robert Kern

"I have come to believe that the whole world is an enigma, a harmless
enigma that is made terrible by our own mad attempt to interpret it as
though it had an underlying truth."
  -- Umberto Eco


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