the performance of pycxx

[<las...@si...>]

I wrote a py extension to calculate fibonacci sequence (i.e. 1 1 2 3 5 ... ) as following
however, I found it is too slow as the table says
 
so, what is the problem? Diid I do something wrong? thanks
 
M    | speed for pure py | speed for pycxx
-----+-----------------------+--------------------
30    |      0.93 sec          |         6.35 sec
40    |     116.64 sec       |        789.91 sec
 
 
[py code]
import time
def fib(n):
    if n<=1:
        return 1
    else:
        return fib(n-1)+fib(n-2)
print fib(M)
st=time.time()
for i in range(M):
    fib(i)
et=time.time()
print 'pure py=%.2f secs' % (et-st)
[/py code]
 
 
[pycxx code]





#ifdef _MSC_VER
#pragma warning(disable: 4786)
#endif
 
#include "CXX/Objects.hxx"
#include "CXX/Extensions.hxx"
 
class fib_module : public Py::ExtensionModule<fib_module>{
public:
    fib_module():Py::ExtensionModule<fib_module>( "fib" ){
    add_varargs_method("fib", &fib_module::fib, "fibonacci sequence function");
    initialize( "this is the test module" );
  }
 
  virtual ~fib_module(){}
 
private:
    Py::Object fib (const Py::Tuple &args){
        args.verify_length(1);
        Py::Long res = args[0];
        if (res<=Py::Long(1))  return Py::Long(1);
        else{
            Py::Tuple a(1), b(1); a[0]=Py::Long(res-2); b[0]=Py::Long(res-1);
            return fib(a)+fib(b);
        }
    }
};
 
#if defined( _WIN32 )
#define EXPORT_SYMBOL __declspec( dllexport )
#else
#define EXPORT_SYMBOL
#endif
 
extern "C" EXPORT_SYMBOL void initfib(){
#if defined(PY_WIN32_DELAYLOAD_PYTHON_DLL)
    Py::InitialisePythonIndirectPy::Interface();
#endif
    static fib_module* fib = new fib_module;
}
 
extern "C" EXPORT_SYMBOL void initfib_d(){ initfib(); }
[/pycxx code]