fix style

mongoengine/context_managers.py

@@ -1,7 +1,7 @@
 from mongoengine.common import _import_class
-from mongoengine.connection import DEFAULT_CONNECTION_NAME, get_db
-from pymongo.write_concern import WriteConcern
 from contextlib import contextmanager
+from pymongo.write_concern import WriteConcern
+from mongoengine.connection import DEFAULT_CONNECTION_NAME, get_db
 
 
 __all__ = ('switch_db', 'switch_collection', 'no_dereference',

mongoengine/document.py

@@ -854,7 +854,7 @@ class Document(BaseDocument):
         collection = cls._get_collection()
         # 746: when connection is via mongos, the read preference is not necessarily an indication that
         # this code runs on a secondary
-        if not collection.database.client.is_mongos and collection.read_preference > 1:
+        if not collection.is_mongos and collection.read_preference > 1:
             return
 
         # determine if an index which we are creating includes