diff --git a/solutions/object_oriented_design/online_chat/online_chat.py b/solutions/object_oriented_design/online_chat/online_chat.py
index c9e5a98..7063ca0 100644
--- a/solutions/object_oriented_design/online_chat/online_chat.py
+++ b/solutions/object_oriented_design/online_chat/online_chat.py
@@ -1,4 +1,5 @@
 from abc import ABCMeta
+from enum import Enum
 
 
 class UserService(object):
diff --git a/solutions/system_design/mint/mint_snippets.py b/solutions/system_design/mint/mint_snippets.py
index 3000d5f..cc5d228 100644
--- a/solutions/system_design/mint/mint_snippets.py
+++ b/solutions/system_design/mint/mint_snippets.py
@@ -1,12 +1,16 @@
 # -*- coding: utf-8 -*-
 
+from enum import Enum
+
+
 class DefaultCategories(Enum):
 
     HOUSING = 0
     FOOD = 1
     GAS = 2
     SHOPPING = 3
-    ...
+    # ...
+
 
 seller_category_map = {}
 seller_category_map['Exxon'] = DefaultCategories.GAS
@@ -44,4 +48,3 @@ class Budget(object):
 
     def override_category_budget(self, category, amount):
         self.categories_to_budget_map[category] = amount
-