recalculating only the new hanchans shoud do the trick now.

the racalc cronjob reports erronous partly recalculations now.
A lot of code cleanups

src/mahjong_ranking/management/commands/update_ranking.py

@@ -5,6 +5,8 @@ Recalculate Mahjong Rankings...
 """
 
 from django.core.management.base import BaseCommand
+
+from mahjong_ranking import LOGGER
 from mahjong_ranking import models
 
 
@@ -14,5 +16,16 @@ class Command(BaseCommand):
     help = "Recalculate all Kyu/Dan Rankings"
 
     def handle(self, *args, **options):
+        old_attr = {'dan': None, 'dan_points': None,
+                    'kyu': None, 'kyu_points': None, 'won_hanchans': None,
+                    'good_hanchans': None, 'hanchan_count': None}
         for ranking in models.KyuDanRanking.objects.all():
+            old_attr = {attr: getattr(ranking, attr) for attr in old_attr.keys()}
             ranking.recalculate()
+            for attr, old_value in old_attr.items():
+                if getattr(ranking, attr) != old_value:
+                    LOGGER.warning(
+                        "%(user)s recalc shows differences in %(attr)s! old: %(old)d, new: %(new)d",
+                        {'user': ranking.user, 'attr': attr,
+                         'old': old_value, 'new': getattr(ranking, attr)}
+                    )