merge.py

def compare_stats(destination_files, destination_folders, source_files, source_empty_folders):
    new_empty_folders = source_empty_folders - destination_folders

    source_dirs = {p.parent for p in source_files}
    destination_dirs = {p.parent for p in destination_files}
    new_directories = source_dirs - destination_dirs

    new_files = source_files - destination_files
    replaced_files = source_files & destination_files
    trumped_files = replaced_files.intersection(source_files | destination_files)

    return (
        new_empty_folders,
        new_directories,
        new_files,
        replaced_files,
        trumped_files
    )

source_at_dest_files = set()
source_at_dest_empty_folders = set()

for source in args.sources:
    source_folder, source_glob = split_folder_glob(source)
    source_files, source_empty_folders = existing_stats(source_folder, source_glob)
    source_at_dest_files.update(source_files)
    source_at_dest_empty_folders.update(source_empty_folders)

    stats = compare_stats(destination_files, destination_empty_folders, source_files, source_empty_folders)

    new_empty_folders, new_directories, new_files, replaced_files, trumped_files = stats
    print(f"New empty folders: {len(new_empty_folders)}")
    print(f"New directories: {len(new_directories)}")
    print(f"New files: {len(new_files)}")
    print(f"Replaced files: {len(replaced_files)}")
    print(f"trumped files: {len(trumped_files)}")