Created attachment 372070 [details]
Example of issue

Hi there,

In the master version of Gnucash the query.search_for() function currently returns the following output:

E.g. the following code:

query = gnucash.Query()
query.search_for(gnucash.gnucash_core_c.GNC_ID_INVOICE)
query.set_book(session.book)
query.run()

Produces the following on the query.search_for line:

* 08:41:59  WARN <qof.class> [qof_class_get_parameter()] no object of type К
* 08:41:59  WARN <qof.class> [qof_class_get_parameter()] no object of type ▒ ▒
* 08:41:59  CRIT <qof.object> [qof_object_foreach()] No object of type ▒ ▒

The query.run line then produces no results.

I believe this issue was introduced in the migration to Python3 - while gnucash.gnucash_core_c.GNC_ID_INVOICE appears to be the correct representation of 'gncInvoice' which is required to be passed though to qof_query_search_for, this function expects it to be a char array, but the Python bindings/SWIG seems to convert it to a Python 3 unicode string somehow causing the errors.

Passing a string though instead of the constant e.g.:

query.search_for('gncInvoice')

Gives the same result

Attepting to pass a byte array though e.g.:

query.search_for(b'gncInvoice')

Gives an incorrect type error in the swig generated code.

I have a feeling a typemap needs to be added to convert from the Python3 string to the char array or something similar but I've been unable to get this to work.

Please find a complete example (which assumes certain MySQL credentials) of the issue which will fail when run in Python 3 (it will work when run in an older version built with Python 2 bindings).