replaced len with count() on a few queries

rowers/models.py

@@ -364,7 +364,7 @@ class Team(models.Model):
 
         if manager.rower.rowerplan in ['plan','pro']:
             otherteams = Team.objects.filter(manager=manager)
-            if len(otherteams) >= 1:
+            if otherteams.count() >= 1:
                 raise ValidationError(
                     "Pro and Self-Coach users cannot have more than one team"
                     )
@@ -569,7 +569,7 @@ def course_length(course):
     if not polygons:
         return 0
 
-    for i in range(len(polygons)-1):
+    for i in range(polygons.count()-1):
         latitude1,longitude1 = polygon_coord_center(polygons[i])
         latitude2,longitude2 = polygon_coord_center(polygons[i+1])
 
@@ -656,7 +656,7 @@ class CoachingGroup(models.Model):
 
     def __len__(self):
         rs = Rower.objects.filter(coachinggroups__in=[self])
-        return len(rs)
+        return rs.count()
 
 # Extension of User with rowing specific data
 @python_2_unicode_compatible
@@ -3133,7 +3133,7 @@ def auto_delete_image_on_delete(sender,instance, **kwargs):
     if instance.filename:
         if os.path.isfile(instance.filename):
             others = GraphImage.objects.filter(filename=instance.filename)
-            if len(others) == 0:
+            if others.count() == 0:
                 os.remove(instance.filename)
         else:
             print("couldn't find the file "+instance.filename)