Working example of kvp acess in Python

[John Ralls]

On Jun 10, 2014, at 8:24 AM, David Osguthorpe wrote:

> On Mon, Jun 09, 2014 at 12:53:38AM +0200, Christoph Holtermann wrote:
>> Hello,
>> 
>> for my python latex invoice script I tried to access the owners data. I tried
>> to work my way to it and came across the kvp system. I made a rude
>> path through there with a working example to access the companies data.
>> 
>> If someone is interested in clarifying the swig qof_instance and kvp_frame
>> stuff for python it would be nice to cooperate.
>> 
>> My branch on github about this is
>> https://github.com/c-holtermann/gnucash/tree/python-kvp
>> 
> 
> Hi
> 
> I have been working with the python bindings but all my knowledge is from my human introspection
> of the existing code
> 
> I have worked on adding the budget - as you have done you add the include files to the
> swig interface file gnucash_core.i and most objects get a base swig interface
> 
> My analysis shows that the bindings then wrap the raw swig objects inside more pythonic classes
> using GnuCashCoreClass as the base object
> 
> so eg in your your case you might want to define     class KvpFrame(GnuCashCoreClass):
> 
> you then add methods by calling the add_methods function
> 
> eg
> 
> KvpFrame.add_methods_with_prefix('kvp_frame_')
> 
> where any c function that starts with the string kvp_frame_ gets added to the class
> This does add all methods that begin with this string - the only methods you can actually
> use in the class though are those where the C kvpframe structure is the first argument
> 
> if methods return special objects the should use methods_return_instances
> to add the return object type
> 
> I have messed a little with the Kvp stuff - one problem is that it tends to return multiple
> types which is not so easy to handle - may have to follow the GList typemap as defined
> in base-typemaps.i

Note that in master, KVP is converted to a private implementation detail of the class that it's attached to, and once C++ conversion gets to the KVP-using classes it will probably get pushed even further down so that it's a persistence detail, existing only in the backends.

In other words, any KVP code you write will break in the next version.

Regards,
John Ralls