[GNC-dev] Python bindings: How to expose additional engine functions

[Steve Brown]

Hi John,

Thanks for the swig link. That's exactly what I need. 

I added the typemaps.i include and the following to gnucash_core.i.

gboolean gncOwnerGetOwnerFromTxn(Transaction *INPUT, GncOwner *OUTPUT);

The *OUTPUT was ignored and arg2 is processed according the
GncOwner(in) typemap.

OTOH:

gboolean gncOwnerGetOwnerFromTxn(Transaction *INPUT, int *OUTPUT);

The value of arg2 after the call is appended to the return as a tuple.
That seems correct.

Any idea?

===

The issue with gnc_get_current_session() is very minor.

I do use a context manager like the example. However, if I call
gnc_get_current_session(), it doesn't know that a session already
exists and creates a new one. That wasn't the behavior I expected.

On the surface, it seems unnecessary to call that function at all.
However, my environment is a plugin with an embedded Python
interpreter. Calls to gnc_get_current_session() are useful and work
just fine. The Python scripts are easier to debug standalone. As this
is unlikely to be an issue for anybody, but me, I can work around it.

Thanks,
Steve 

On Tue, 2023-01-24 at 14:37 -0800, John Ralls wrote:
> 
> 
> > On Jan 24, 2023, at 2:03 PM, Steve Brown <sbrown at opensat.com>
> > wrote:
> > 
> > My use case is accessing owner name and address from a transaction.
> > The transaction is found by guid.
> > 
> > Exposing guid_from_string() was pretty straightforward as was
> > GetLot()
> > and GetFirstAPARAcctSplit().
> > 
> > I also need GetOwnerFromTxn or GetOwnerFromLot. However, this and
> > many
> > similar functions return the result through an argument and
> > indicate
> > success or failure by returning a boolean. It's not clear whether
> > there
> > is an general way with swig to deal with this other than adding a
> > wrapper to return the result and indicate failure by returning
> > NULL.
> 
> Yes, but SWIG makes it pretty simple, see
> https://www.swig.org/Doc3.0/Python.html#Python_nn46.
> Note that you can still have the bool rv to test success.
> 
> > I also noticed that there is a problem with gnc-
> > session.c:gnc_get_current_session() using the bindings. In the
> > executable, gnc_set_current_session() is called in gnc_file.c after
> > each qof_session_new(). But with the Python bindings, the swig-
> > generated code calls qof_session_new(). So, current_session isn't
> > initialized and the first call subtly creates a new session. I
> > added a
> > gnc_set_current_session() call to qof_session_new() and that fixed
> > things for me . I don't think that's the best solution.  
> 
> Neither set_ nor get_current_session are wrapped. You should be
> creating a Python Session object,
> bindings/python/examples/simple_book.py.
> 
> Regards,
> John Ralls
>