Setting archiver.archive_generator doesn't work

This is because the default value is taken from the field too early
diff --git a/tools/import-mbox.py b/tools/import-mbox.py
index 201988f..33eccf2 100755
--- a/tools/import-mbox.py
+++ b/tools/import-mbox.py
@@ -122,7 +122,10 @@
         mboxfile = ""
         filename = ""
 
-        archie = archiver.Archiver(parse_html=parseHTML)
+        if args.generator:
+            archie = archiver.Archiver(generator=args.generator, parse_html=parseHTML)            
+        else:
+            archie = archiver.Archiver(parse_html=parseHTML)            
 
         while len(lists) > 0:
             self.printid("%u elements left to slurp" % len(lists))
@@ -456,9 +459,6 @@
         print("Error: unable to check if the index %s exists!: %s" % (dbname, err))
         sys.exit(1)
 
-if args.generator:
-    archiver.archiver_generator = args.generator
-
 def globDir(d):
     dirs = [ f for f in listdir(d) if isdir(join(d,f)) ]
     mboxes = [ f for f in glob.glob(join(d,"*" + extension)) if isfile(f) ]