Restructure code to make it slightly less monolithic (though client.py module is still over 3,800 lines long) - place each class in a separate module; place exceptions, strings and constants in separate modules.
Address some of the easier lint advisories (using pylint v2.17) - client.py lint score increased from 8.42 to 9.42. Note that many pre-existing lint issues remain, including apparently some Error categories.
No (intentional) changes in functionality.