成功编译后无法导入已编译的cython函数

Question

I'm testing out Cython on Windows 10 (Spyder 3.2.3) and Python 3.6.3 following the Tutorial , and I wrote this function:

from libc.stdlib cimport malloc, free

cdef int** t3(int* El, int lEl):
    cdef int lElsq = lEl*lEl
    cdef int i,j
    cdef int** rr = <int**> malloc(2*sizeof(int*))
    for i in range(2):
        rr[i] = <int*> malloc(lElsq*sizeof(int))
    for i in range(lEl):
        for j in range(lEl):
            rr[0][i*lEl+j] = El[i]
            rr[1][i*lEl+j] = El[j]
    return rr

I put it into a pyx file and following the tutorial compiled it using the MS Visual Studio 14 compiler.

Command: %run setup.py build_ext --inplace

Setup file:

from distutils.core import setup
from Cython.Build import cythonize

setup(
    ext_modules=cythonize("tempCython.pyx"),
)

The compilation didn't throw any error and a lot of files were created:

In the same directory as the original file:

• a tempCython.c file of the same name
• a tempCython.cp36-win_amd64.pyd file

In the subdirectory build\\temp.win-amd64-3.6\\Release :

• a tempCython.obj file
• a tempCython.cp36-win_amd64.exp file
• a tempCython.cp36-win_amd64.lib file

The Cython tutorial tells me I need the pyd file, so I removed the cp36-win_amd64 in the filename.

I can import it without error, but my function t3 just never shows up, it's simply not there.

Without any kind of error message I'm at a loss now. I have encountered errors like these before sometimes in 3rd-party packages, but I never understood what caused them. Why is my function not there?

I'd also like to know the point of all those additional files, which ones do I actually need?

Answer 1

You have written a cdef function and are trying to call it from python. Unfortunately, cdef functions are not visible from python (see http://docs.cython.org/en/latest/src/userguide/language_basics.html#python-functions-vs-c-functions ) so you need to do a little bit more work to expose your function to python. In particular you would need to write either a def function or a cpdef function that calls your cdef function and then call that function from python.