diff --git a/README-ja.md b/README-ja.md
index 0f003b2d..9afd5f92 100644
--- a/README-ja.md
+++ b/README-ja.md
@@ -1172,7 +1172,7 @@ def get_user(self, user_id):
     if user is None:
         user = db.query("SELECT * FROM users WHERE user_id = {0}", user_id)
         if user is not None:
-            key = "user.{0}".format(user_id)
+            key = f"user.{user_id}"
             cache.set(key, json.dumps(user))
     return user
 ```
diff --git a/README-zh-Hans.md b/README-zh-Hans.md
index 368f588a..f40e80c8 100644
--- a/README-zh-Hans.md
+++ b/README-zh-Hans.md
@@ -1181,7 +1181,7 @@ def get_user(self, user_id):
     if user is None:
         user = db.query("SELECT * FROM users WHERE user_id = {0}", user_id)
         if user is not None:
-            key = "user.{0}".format(user_id)
+            key = f"user.{user_id}"
             cache.set(key, json.dumps(user))
     return user
 ```
diff --git a/README-zh-TW.md b/README-zh-TW.md
index d805e7e0..1b7b84d5 100644
--- a/README-zh-TW.md
+++ b/README-zh-TW.md
@@ -1173,7 +1173,7 @@ def get_user(self, user_id):
     if user is None:
         user = db.query("SELECT * FROM users WHERE user_id = {0}", user_id)
         if user is not None:
-            key = "user.{0}".format(user_id)
+            key = f"user.{user_id}"
             cache.set(key, json.dumps(user))
     return user
 ```
diff --git a/README.md b/README.md
index 952c7fbe..2384c410 100644
--- a/README.md
+++ b/README.md
@@ -1221,7 +1221,7 @@ def get_user(self, user_id):
     if user is None:
         user = db.query("SELECT * FROM users WHERE user_id = {0}", user_id)
         if user is not None:
-            key = "user.{0}".format(user_id)
+            key = f"user.{user_id}"
             cache.set(key, json.dumps(user))
     return user
 ```
diff --git a/solutions/object_oriented_design/call_center/call_center.ipynb b/solutions/object_oriented_design/call_center/call_center.ipynb
index c540c6a6..803ee9cc 100644
--- a/solutions/object_oriented_design/call_center/call_center.ipynb
+++ b/solutions/object_oriented_design/call_center/call_center.ipynb
@@ -158,7 +158,7 @@
     "\n",
     "    def dispatch_call(self, call):\n",
     "        if call.rank not in (Rank.OPERATOR, Rank.SUPERVISOR, Rank.DIRECTOR):\n",
-    "            raise ValueError('Invalid call rank: {}'.format(call.rank))\n",
+    "            raise ValueError(f'Invalid call rank: {call.rank}')\n",
     "        employee = None\n",
     "        if call.rank == Rank.OPERATOR:\n",
     "            employee = self._dispatch_call(call, self.operators)\n",
diff --git a/solutions/object_oriented_design/call_center/call_center.py b/solutions/object_oriented_design/call_center/call_center.py
index 1d5e7bc6..205a9b15 100644
--- a/solutions/object_oriented_design/call_center/call_center.py
+++ b/solutions/object_oriented_design/call_center/call_center.py
@@ -94,7 +94,7 @@ class CallCenter(object):
 
     def dispatch_call(self, call):
         if call.rank not in (Rank.OPERATOR, Rank.SUPERVISOR, Rank.DIRECTOR):
-            raise ValueError('Invalid call rank: {}'.format(call.rank))
+            raise ValueError(f'Invalid call rank: {call.rank}')
         employee = None
         if call.rank == Rank.OPERATOR:
             employee = self._dispatch_call(call, self.operators)
diff --git a/solutions/object_oriented_design/deck_of_cards/deck_of_cards.ipynb b/solutions/object_oriented_design/deck_of_cards/deck_of_cards.ipynb
index 1a9bc1c5..dccbee18 100644
--- a/solutions/object_oriented_design/deck_of_cards/deck_of_cards.ipynb
+++ b/solutions/object_oriented_design/deck_of_cards/deck_of_cards.ipynb
@@ -109,7 +109,7 @@
     "        if 1 <= new_value <= 13:\n",
     "            self._value = new_value\n",
     "        else:\n",
-    "            raise ValueError('Invalid card value: {}'.format(new_value))\n",
+    "            raise ValueError(f'Invalid card value: {new_value}')\n",
     "\n",
     "\n",
     "class Hand(object):\n",
diff --git a/solutions/object_oriented_design/deck_of_cards/deck_of_cards.py b/solutions/object_oriented_design/deck_of_cards/deck_of_cards.py
index a4708758..94f8b105 100644
--- a/solutions/object_oriented_design/deck_of_cards/deck_of_cards.py
+++ b/solutions/object_oriented_design/deck_of_cards/deck_of_cards.py
@@ -55,7 +55,7 @@ class BlackJackCard(Card):
         if 1 <= new_value <= 13:
             self._value = new_value
         else:
-            raise ValueError('Invalid card value: {}'.format(new_value))
+            raise ValueError(f'Invalid card value: {new_value}')
 
 
 class Hand(object):