I have a script which tries to get a list of all customers from GnuCash. The relevant part is:

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from gnucash import Query
from gnucash.gnucash_core_c import GNC_ID_CUSTOMER

query = Query()
query.search_for(GNC_ID_CUSTOMER)
query.set_book(s.book)
customers = []
for index, result in enumerate(query.run()):
  customer = Customer(instance=result)
  customers.append(customer)

query.destroy()

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I sucessfully used this with GnuCash 2.6 under Python 2 but it does not work anymore with Python 3 on GnuCash 3.0. This is the output I get:

* 17:33:44  WARN <qof.class> [qof_class_get_parameter()] no object of type qof_class_get_parameter
* 17:33:44  WARN <qof.class> [qof_class_get_parameter()] no object of type qof_class_get_parameter
* 17:33:44  CRIT <qof.object> [qof_object_foreach()] No object of type qof_object_foreach

Replacing the GNC_ID with the string 'gncCustomer' like done in the gnucash_rest example [1] does not help either.

The culprint seems to be the query.run() command. Even when leaving out the entire loop and just stating query.run(), the mentioned messages are printed.

[1] https://github.com/Gnucash/gnucash/blob/5e807a0e18f7ac90158f6ee4dac0920545fde7cc/bindings/python/example_scripts/rest-api/gnucash_rest.py#L768

Using Gentoo Linux.