[Numpy-discussion] Type declaration to include all valid numerical NumPy types for Cython

[Ilhan Polat]

Hi all,

As you might have seen my recent mails in Cython list, I'm trying to cook
up an input validator for the linalg.solve() function. The machinery of
SciPy linalg is as follows:

Some input comes in passes through np.asarray() then depending on the
resulting dtype of the numpy array we choose a LAPACK flavor (s,d,c,z) and
off it goes through f2py to lalaland and comes back with some result.

For the backslash polyalgorithm I need the arrays to be contiguous (C- or
F- doesn't matter) and any of the four (possibly via making new copies)
float, double, float complex, double complex after the intake because we
are using wrapped fortran code (LAPACK) in SciPy. So my difficulty is how
to type such function input, say,

ctypedef fused numeric_numpy_t:
    bint
    cnp.npy_bool
    cnp.int_t
    cnp.intp_t
    cnp.int8_t
    cnp.int16_t
    cnp.int32_t
    cnp.int64_t
    cnp.uint8_t
    cnp.uint16_t
    cnp.uint32_t
    cnp.uint64_t
    cnp.float32_t
    cnp.float64_t
    cnp.complex64_t
    cnp.complex128_t

Is this acceptable or something else needs to be used? Then there is the
storyof np.complex256 and mysterious np.float16. Then there is the Linux vs
Windows platform dependence issue and possibly some more that I can't
comprehend. Then there are datetime, str, unicode etc. that need to be
rejected. So this is quickly getting out of hand for my small brain.

To be honest, I am a bit running out of steam working with this issue even
though I managed to finish the actual difficult algorithmic part but got
stuck here. I am quite surprised how fantastically complicated and
confusing both NumPy and Cython docs about this stuff. Shouldn't we keep a
generic fused type for such usage? Or maybe there already exists but I
don't know and would be really grateful for pointers.

Here I wrote a dummy typed Cython function just for type checking:

cpdef inline bint ncc( numeric_numpy_t[:, :] a):
    print(a.is_f_contig())
    print(a.is_c_contig())

    return a.is_f_contig() or a.is_c_contig()

And this is a dummy loop (with aliases) just to check whether fused type is
working or not (on windows I couldn't make it work for float16).

for x in (np.uint, np.uintc, np.uintp, np.uint0, np.uint8, np.uint16,
np.uint32,
          np.uint64, np.int, np.intc, np.intp, np.int0, np.int8, np.int16,
          np.int32,np.int64, np.float, np.float32, np.float64, np.float_,
          np.complex, np.complex64, np.complex128, np.complex_):
    print(x)
    C = np.arange(25., dtype=x).reshape(5, 5)
    ncc(C)


Thanks in advance,
ilhan
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