???double[2]???  summa( const double* pnts, const int n) {
   double tmp0,tmp1; 
   int i;
   tmp0 = 0.0;
   tmp1 = 0.0;
   for(i=0; i<n; ++i) {
       tmp0+=*(pnts+2*i);
       tmp1+=*(pnts+2*i+1);
   }
//   printf("tmp=%lf\n",tmp);
   return ????;
}

mod_test=numpy.ctypeslib.load_library('libtest', '.')
mass=numpy.ndarray(2*n,dtype='d')
...
result=mod_test.summa(mass.ctypes.data,n)

# python:
a=numpy.zeros(n,dtype='d')
b=numpy.zeros(2,dtype='d')
n=10
mod_test.summa(a.ctype.data,b.ctype.data,n)

// C:
void summa(const double* a,double* b,int n)
{
 ....
}