Issues with GList Arguments in Python Bindings?

[Oliver Trevor]

Hello John,

     I have submitted a PR (https://github.com/Gnucash/gnucash/pull/2066). I added type translators for all the types that were supported by the typemap(out) for GList but have only tested with lists of GncLot objects, as I am not sure where to find existing C functions that take some of the other types of lists. This at least fixes the issue with Customer.ApplyPayment not working at all from Python.

Thanks,
Oliver Trevor
________________________________
From: John Ralls <jralls at ceridwen.us>
Sent: Saturday, March 8, 2025 11:26 PM
To: Oliver Trevor <olt at mit.edu>
Cc: gnucash-devel at gnucash.org <gnucash-devel at gnucash.org>
Subject: Re: Issues with GList Arguments in Python Bindings?



On Mar 8, 2025, at 14:57, Oliver Trevor <olt at mit.edu> wrote:

Hello Gnucash developers,

      I was attempting to use the Gnucash Python bindings to apply payments to a list of invoices using Customer.ApplyPayment (which maps to gncOwnerApplyPaymentSecs on the C side), but it gives an error "TypeError: in method 'gncOwnerApplyPaymentSecs', argument 3 of type 'GList *'" when I attempt to pass a Python list of lots as the second argument "lots" (third argument on the C side).

     Looking at how the SWIG bindings were written, I think the issue may be that there is not a type translator that turns Python lists into GList. base-typemaps.i has a SWIG type translator on line 269 that converts Python lists into GSList objects, but as far as I can tell there isn't one that converts Python lists into GList objects.

     Am I correct that this is an issue, or am I missing how the bindings are intended to be used? If it's an issue, I could work on a PR to add a type translator for GList. Also, has anybody ever tried making bindings using GObject introspection instead of SWIG, since Gnucash's API is already GLib-based?

Oliver,

Looks to like you’re right. There are several SCM List <-> GList* typemaps but only a typemap(out) for Python, not useful for passing arguments into a C function. Go ahead and write a PR.

I don’t think anyone has considered GI. While somebody made a start on GI bindings for Guile (https://github.com/spk121/guile-gi) it’s a fairly recent (started in 2019) project and seems to have been abandoned a couple of years ago. Meanwhile on the GnuCash side while it’s true that we have GObject-based classes,  their memory management wasn’t done correctly and probably wouldn’t integrate well with GI. Our long-term goal is to reimplement them as C++ objects.

Regards,
John Ralls

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