Question

I want to call c written functions with complex numbered inputs and in python. I’ve tried using SWIG to generate a wrapper – but it seems to fall down. I think i need to work out the proper ‘macro’ for use in numpy.i – but not sure what it is – anyone have any experience in this – or other ways I can work around this?

The numpy.i shows this at the bottom – although it has been commented out. I tried using these macros – but they fail, SWIG complains about a syntax error for the following macro expansions I tried:

%numpy_typemaps(complex float, NPY_CFLOAT , int)
%numpy_typemaps(complex double, NPY_CDOUBLE, int)
%numpy_typemaps(complex long double, NPY_CLONGDOUBLE, int)

These are my files:

ComplexNumbers.c

# include <math.h>
# include <complex.h>


double complex returnX(double complex X) 
/*
    fresnel reflection coefficient rs
*/
{
    return X;
}

ComplexNumbers.i:

%{
#define SWIG_FILE_WITH_INIT
%}
%include "numpy.i"
%init %{
import_array();
%}


%module ComplexNumbers

%inline %{
extern double complex returnX(double complex X);
%}

Python:

#!/usr/bin/env python

"""
setup.py file for ComplexNumbers
"""

from distutils.core import setup
from distutils.extension import Extension

import numpy


ComplexNumbers_module = Extension('_ComplexNumbers',
                           sources=['ComplexNumbers_wrap.c', 
                                    'ComplexNumbers.c'],
                           include_dirs=[numpy.get_include()]
                           )

setup (name = 'ComplexNumbers',
       version = '1.0',
       author      = "JP Hadden [e-mail]",
       description = """Spectral Interfereometry functions""",
       ext_modules = [ComplexNumbers_module],
       py_modules = ["ComplexNumbers"],
       )

Error output from compiler

C:\MinGW32-xy\bin\gcc.exe -mno-cygwin -mdll -O -Wall -IC:\Python27\lib\site-pack
ages\numpy\core\include -IC:\Python27\include -IC:\Python27\PC -c ComplexNumbers
_wrap.c -o build\temp.win32-2.7\Release\complexnumbers_wrap.o
ComplexNumbers_wrap.c:2975:23: error: expected '=', ',', ';', 'asm' or '__attrib
ute__' before 'returnX'
ComplexNumbers_wrap.c: In function '_wrap_returnX':
ComplexNumbers_wrap.c:2982:18: error: expected '=', ',', ';', 'asm' or '__attrib
ute__' before 'arg1'
ComplexNumbers_wrap.c:2982:18: error: 'arg1' undeclared (first use in this funct
ion)
ComplexNumbers_wrap.c:2982:18: note: each undeclared identifier is reported only
 once for each function it appears in
ComplexNumbers_wrap.c:2986:18: error: expected '=', ',', ';', 'asm' or '__attrib
ute__' before 'result'
ComplexNumbers_wrap.c:2986:18: error: 'result' undeclared (first use in this fun
ction)
ComplexNumbers_wrap.c:2997:24: error: expected ')' before 'complex'
ComplexNumbers_wrap.c:2997:24: error: pointer value used where a floating point
value was expected
ComplexNumbers_wrap.c:2997:14: error: invalid type argument of unary '*' (have '
double')
ComplexNumbers_wrap.c:3000:20: error: expected ')' before 'complex'
ComplexNumbers_wrap.c:3000:20: warning: implicit declaration of function 'return
X'
ComplexNumbers_wrap.c:3001:15: error: expected ')' before 'complex'
ComplexNumbers_wrap.c:3001:15: error: expected ')' before 'complex'
ComplexNumbers_wrap.c:3001:15: error: expected ')' before 'complex'
ComplexNumbers_wrap.c:3001:15: error: pointer value used where a floating point
value was expected
ComplexNumbers_wrap.c:3001:15: error: expected ')' before 'complex'
ComplexNumbers_wrap.c:3001:15: error: incompatible type for argument 1 of 'memcp
y'
c:\mingw32-xy\bin\../lib/gcc/mingw32/4.5.2/../../../../include/string.h:38:40: n
ote: expected 'void *' but argument is of type 'double'
error: command 'gcc' failed with exit status 1

Answer 1

I’m not sure how this interacts with Numpy, but SWIG certainly includes support for C99’s complex types. I was able to verify this with the following example:

%module test
%{
#include <complex.h>
%}

%include <complex.i>

%inline %{
  double complex test(double complex X) {
    return X;
  }
%}

This uses the SWIG complex.i interface.

(Note that here %inline is used to declare, define and wrap all in one place – handy for testing, but for ‘real’ code I tend to use %include).

I compiled this (on Linux) with:

swig -Wall -python test.i 
gcc -std=c99 -Wall -Wextra test_wrap.c -I/usr/include/python2.7 -shared -o _test.so

Which built fine with only one warning. Once that was done I could then do:

LD_LIBRARY_PATH=.  python                       
Python 2.7.3 (default, Aug  1 2012, 05:16:07) 
[GCC 4.6.3] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> import test
>>> test.test(complex(0,1))
1j
>>> test.test(complex(0,2))
2j
>>> test.test(complex(1,2))
(1+2j)
>>> 

Which seems to be accepting and returning native Python complex types.

I was also able to make the following interface compile:

%{
#define SWIG_FILE_WITH_INIT
#include <complex.h>
%}
%include <complex.i>
%include <numpy.i>
%init %{
import_array();
%}

%numpy_typemaps(complex float, NPY_CFLOAT , int)
%numpy_typemaps(complex double, NPY_CDOUBLE, int)
%numpy_typemaps(complex long double, NPY_CLONGDOUBLE, int)

%module test

%inline %{
  double complex test(double complex X) {
    return X;
  }
%}

With the addition of %include <complex.i> and -std=c99 to the compiler flags. I think you can make distutils set that for you using something like these options.