swig: add helper get_PySwigObject

Author: jcarpent

include/eigenpy/swig.hpp

@@ -5,6 +5,8 @@
 #ifndef __eigenpy_swig_hpp__
 #define __eigenpy_swig_hpp__
 
+#include "eigenpy/fwd.hpp"
+
 namespace eigenpy
 {
   struct PySwigObject
@@ -13,6 +15,19 @@ namespace eigenpy
     void * ptr;
     const char * desc;
   };
+
+  inline PySwigObject * get_PySwigObject(PyObject * pyObj)
+  {
+    if(!PyObject_HasAttrString(pyObj,"this"))
+      return NULL;
+    
+    PyObject * this_ptr = PyObject_GetAttrString(pyObj,"this");
+    if(this_ptr == NULL)
+      return NULL;
+    PySwigObject * swig_obj = reinterpret_cast<PySwigObject*>(this_ptr);
+    
+    return swig_obj;
+  }
 }
 
 #endif // ifndef __eigenpy_swig_hpp__