> On Aug 5, 2018, at 5:17 PM, c.holterm...@gmx.de wrote: > > Hello, > > after some time I get back to the gnucash python bindings. > > I worked on a str method for GncNumeric. It's in the example_script > dir > (https://github.com/Gnucash/gnucash/blob/maint/bindings/python/example_scripts/str_methods.py) > I changed it to python3. Then I began to wonder about the relationshipp of > the SwigObject and the wrapping object. > > In this case it's something like > <gnucash.gnucash_core_c._gnc_numeric; proxy of <Swig Object of type > '_gnc_numeric *' at 0x7f11908da840> > > and > <gnucash.gnucash_core.GncNumeric object at 0x7f118f76d6d8> > > When I have the GncNumeric object I can access the SwigObject through its > instance property. > The other way round seems not as simple. > > My method __gncnumeric__str__ overwrites the __str__ method using add_method. > > In this method self points to the swig object. I cannot use the methods of > GncNumeric as > it is the layer of the wrapping object. > > To access these methods I used to instantiate a GncNumeric(instance=self) as > a temporary self. > But that seems not right as this probably already exists. > > I wondered if I could know about the wrapping object when I had the instance > only. I did not > find a way. I stumbled over an interesting comment in > https://github.com/Gnucash/gnucash/blob/69fef8277fde56e7d2df700b21c63c19c115852a/bindings/python/function_class.py#L50 > > # why reimpliment __new__? Because later on we're going to > # use new to avoid creating new instances when existing instances > # already exist with the same __instance value, or equivalent __instance > # values, where this is desirable... > > I did not find "later on". But if that works I can safely do > GncNumeric(instance=self) as it > would reuse the existing GncNumeric object. > > But nevertheless I wondered if we could put a link to the GncNumeric in the > Swig Level. I tried > it: > https://github.com/c-holtermann/gnucash/commit/a6c2adf7d29c4367728a4fa920307ee595eefa5a > (link to my fork) > > Interstingly some Swig objects can be added to and some others not. > GncNumeric works while > QofSession doesn't. So I made it a try block for now. > > Having done that I can get to the GncNumeric (sort of higher self) from the > Swig object: > https://github.com/c-holtermann/gnucash/commit/2f35b550709ad4131aca0e7309f6bb4b0f984b84 > > Well I found it interesting to think these things through. Maybe someone can > tell me about > the mysterious "later on" in the cited comment. At this point I find it > useful to have a > way from the instance to the wrapping object through some kind of link as I > suggested in > the patch to function_class.
Christoph, The person who wrote the first two lines of that, Mark Jenkins, was the original source of the Python bindings. He was never a regular dev, he just got 16 patches committed between 2007 and 2012, 10 of which touched the python bindings. Your history with them is almost as long as his--in fact you have *12* commits--and pretty much no one else has done anything serious with them. In other words, if anyone knows, it’s you! Just to add some more confusion, there’s now a C++ class GncNumeric that handles the actual implementation of many of the gnc_numeric.* functions. I believe that SWIG can’t see it, only the C wrapper functions are exposed to SWIG. Regards, John Ralls _______________________________________________ gnucash-devel mailing list gnucash-devel@gnucash.org https://lists.gnucash.org/mailman/listinfo/gnucash-devel
