Authoring catalogs in PythonAttached are Python scripts for writing gThumb catalogs in the old GQView (.gqv) format (version <=2.10) (get script) and in the new XML (.catalog) format (version 2.11) (get script).
from gthumb import make_library, write_catalog
gthumb_library_path = make_library("Library Name")
write_catalog(files_list, "Catalog Name", gthumb_library_path)
files_listis a list of either relative or absolute paths. To open your new catalog in
from gthumb import write_and_open_catalog
For the lastest
gthumbrelease, follow the installation instructions here.