Make .lib file for cython with Visual C++ for Python

[havsula]

Hello

I have some c-code I want to include in Python by using Cython. Name of the c-file is cmean.c. I also have a cmean.h which define the function in cmean.c.

Have the following c-wrapper file:

# m.pyx

cdef extern from "cmean.h":

    double mean(int, double*)

from stdlib cimport *

def cmean(a):

    n = len(a)

    cdef double *v

    v = malloc(n*sizeof(double))

    for i in range(n):

        v[i] = float(a[i])

    m = mean(n, v)

    free(v)

    return m

And this setup.py

from setuptools import Extension

from Cython.Build import cythonize

from Cython.Distutils import build_ext

ext_modules=[Extension("lib",

    sources = ["m.pyx"],

    libraries=['cmean']

    )] # Unix-like specific

setup(

    name = "Demos",

    ext_modules = cythonize(ext_modules),

    cmdclass = {'build_ext':build_ext}

    )

But I need to make the cmean.c into a library which Cython can use. I have used the following commands

cl.exe /c cmean.c

lib.exe /out:cmean.lib cmean.obj

This makes a cmean.lib file but when I try to run setup.py I got the following error:

E:\GD\UD\Software\CythonTest\calling-c\test2>python setup.py build_ext --inplace

running build_ext

building 'lib' extension

creating build

creating build\temp.win32-2.7

creating build\temp.win32-2.7\Release

C:\Users\trofl\AppData\Local\Programs\Common\Microsoft\Visual C++ for Python\9.0\VC\Bin\cl.exe /c /nologo /Ox /MD /W3 /GS- /DNDEBUG -IC:\Anaconda2\include -IC:\Anaconda2\PC /Tccfib.c /Fobuild\temp.win32-2.7\Release\cfib.obj

cfib.c

creating build\lib.win32-2.7

C:\Users\trofl\AppData\Local\Programs\Common\Microsoft\Visual C++ for Python\9.0\VC\Bin\link.exe /DLL /nologo /INCREMENTAL:NO /LIBPATH:C:\Anaconda2\libs /LIBPATH:C:\Anaconda2\PCbuild /LIBPATH:C:\Anaconda2\PC\VS9.0 /EXPORT:initlib build\temp.win32-2.7\Release\cfib.obj /OUT:build\lib.win32-2.7\lib.pyd /IMPLIB:build\temp.win32-2.7\Release\lib.lib /MANIFESTFILE:build\temp.win32-2.7\Release\lib.pyd.manifest

LINK : error LNK2001: unresolved external symbol initlib

build\temp.win32-2.7\Release\lib.lib : fatal error LNK1120: 1 unresolved externals

error: command 'C:\\Users\\trofl\\AppData\\Local\\Programs\\Common\\Microsoft\\Visual C++ for Python\\9.0\\VC\\Bin\\link.exe' failed with exit status 1120

So there is something I do wrong when making the .lib file.

I have no trouble compiling .pyx files.

[havsula]

SOLVED

After a lot of googling I found that setting the library name equal to the .pyx file name did the trick:

ext_modules=[Extension("m",

    sources = ["m.pyx"],

    libraries=['cmean']

    )] # Unix-like specific

Do not understand why this helps, but it works!!!

[Chris Barker]

chances are you would be better off simply compiling your c file in with your extension.

you only want tp build a lib if it's large, and you want to be able to access it from multiple extension files. if your extension is a wrapper around a single, simple C file, then just build it all as one. Something like:

ext_modules=[Extension("lib",
    sources = ["m.pyx", "cmean.c"]

    ) 

]

simple, eh? :-)

--

Christopher Barker, Ph.D.
Oceanographer

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Chris....@noaa.gov

[Robert Bradshaw]

On Sat, Dec 26, 2015 at 2:34 AM, havsula <tro...@gmail.com> wrote:
> SOLVED
> After a lot of googling I found that setting the library name equal to the
> .pyx file name did the trick:

Yes, just like Python, the module "m" is in a file named "m.py" or "m.pyx"

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