[GNC-dev] Python Binding: GncOwner fails to convert from C->Python->C

[john]

Yes, it does look like the in type map ignores the out typemap's tuple and tries to convert it into a pointer. That won't work. It should be something like

if (! PyTuple_Ceck($input))
    return NULL; 

GncOwnerType type = (GncOwnerType)PyLong_asLong(PyTuple_GetItem($input, 0));
PyObject* py_instance = PyTuple_GetItem($input, 1);
void* instance = NULL;
GncOwner* owner = gncOwnerNew()
switch (type)
{
    case GNC_OWNER_CUSTOMER:
         if (SWIG_ConvertPtr(py_instance, &instance,
                                         $descriptor(GncCustomer *),
                                         SWIG_POINTER_EXCEPTION)) == 0)
          {
               gncOwnerInitCustomer(owner, (GncCustomer *)instance);
               $1 = owner;
          }      
             
    /* ... */
}

/* Something failed */
gnc_owner_free(owner);
PyErr_SetString( PyExc_ValueError,
                        "Python object passed to function with GncOwner * argument "
                        "couldn't be converted back to pointer of that type");
 $1 = NULL;

That's untested off the top of my head, obvs you need to fill in the other types. It should correctly make a GncOwner* to pass back to functions that take one.

Now if you actually need the instance pointer you'll want to write a typemap(in) for each one that you need. It will probably be cleanest to extract the tuple item in python and pass that, letting the new %typemap(in) convert it to a C pointer.

Geert, those typemaps are yours, written 11  years ago. Any comments?

Regards,
John Ralls

> On Jan 29, 2023, at 5:38 AM, Steve Brown <sbrown at opensat.com> wrote:
> 
> I get a Python GncOwner object returned to Python. It appears well
> formed.
> 
> owner:  <class 'gnucash.gnucash_core.GncOwner'> <gnucash.gnucash_core.GncOwner object at 0x7f33d4cc3050>
> owner_instance:  <class 'tuple'> (4, <Swig Object of type 'GncVendor *' at 0x7f214b5a9500>)
> 
> It's not clear how to easily inspect the Swig object.
> 
> However, the object doesn't convert back to C. It's not recognized as
> GncVendor.
> 
> I get:
> 
> ValueError: Python object passed to function with GncOwner * argument couldn't be converted back to pointer of that type
> 
> The out typemap for GncOwner looks correct. However, I can't see how
> the in typemap gets the swig wrapper object from the tuple created by
> the out typemap. 
>  
> I can recreate the problem in simple_business_create.py with the
> attached patch.
> 
> If there is nothing obviously wrong with the typemaps, how should I go
> about debugging this?
> 
> Thanks,
> Steve
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