CODEWITHSUNDEEP
pythonc++swig
GeorgeWilson
GeorgeWilson

Reputation: 592

Error wrapping Eigen/C++ with Python using Swig

I'm having trouble wrapping a small project that uses Eigen (the linear algebra package) using SWIG. I'm getting a python error that I don't understand and can't find much about online - but I suspect there is some C++ memory corruption somewhere. I've boiled this down to a toy example.. but unfortunately it's still reasonable long:

--- testfunc.cxx ----

#include "Eigen/Dense" 

Eigen::VectorXd test(Eigen::MatrixXd data){ 
        Eigen::VectorXd temp; 
        return temp; 
}

--- testswig.i -----

%module testswig 

%{ 
#define SWIG_FILE_WITH_INIT 
#include "Eigen/Core" 
#include <Python.h>
#include <numpy/arrayobject.h>
#include "testfunc.cxx" 

%} 

%init 
%{ 
  import_array(); 
%} 

%include "numpy.i" 

%typemap(out) Eigen::VectorXd 
{ 
    npy_intp dims[1] = {$1.size()}; 
    PyObject* array = PyArray_SimpleNew(1, dims, NPY_DOUBLE); 
    double* data = ((double *)PyArray_DATA( array )); 
    for (int i = 0; i != dims[0]; ++i){ 
        *data++ = $1.data()[i]; 
    } 
    $result = array; 
} 

%typemap(in) Eigen::MatrixXd (Eigen::MatrixXd TEMP) 
{ 

  int rows = 0; 
  int cols = 0; 

  rows = PyArray_DIM($input,0); 
  cols = PyArray_DIM($input,1); 

  PyArrayObject* temp; 
  PyArg_ParseTuple($input, "O", &temp);   

  TEMP.resize(rows,cols); 
  TEMP.fill(0); 

  double *  values = ((double *) PyArray_DATA($input)); 
  for (long int i = 0; i != rows; ++i){ 
      for(long int j = 0; j != cols; ++j){ 
          // std::cout << "data " << data[i] << std::endl; 
          TEMP(i,j) = values[i*rows+j]; 
      } 
  }   

} 

%include "testfunc.cxx"

--- setup.py ----

from distutils.core import setup, Extension 
import numpy 
numpyinclude = numpy.__file__[:-12] + 'core/include/' 
testswig = Extension('_testswig', 
                     sources=['testswig_wrap.cxx'], 
                     include_dirs=['../', numpyinclude]) 

setup (name = 'testswig', 
       version = '0.1', 
       author      = "NoName", 
       description = """ """, 
       ext_modules = [testswig], 
       py_modules = ["testswig"])

----- building ------

I am building this in a folder with all 3 files and a folder 'Eigen' containing the Eigen headers. The commands are : 

swig -c++ -python -I./ testswig.i 
python setup.py install

------- error ----------

Then I run a python file containing 

import testswig 
import numpy as np 
print testswig.test(np.array([[2,3],[4,5]]))

Which gives the error "SystemError: new style getargs format but argument is not a tuple".

Note a few things: 1) The same commands run fine directly from a python interpreter. 2) If the function does not return an Eigen::VectorXd, or does not take an Eigen:MatrixXd, it works fine.

Thanks for your time.

Upvotes: 2

Views: 1677

Answers (1)

Flexo - Save the data dump
Flexo - Save the data dump

Reputation: 88751

In your in typemap you have:

PyArrayObject *temp;
PyArg_ParseTuple($input, "O", &temp);

This is incorrect - $input is a PyObject that has already been extracted from the arguments at this stage, but not a tuple, so you want:

PyArrayObject *temp=NULL;
if (PyArray_Check($input))
    temp = (PyArrayObject*)$input;

To verify that it's the correct type and then cast if it is.

Upvotes: 3

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