diff --git a/personal_data/fetchers/wanikani_lessons.py b/personal_data/fetchers/wanikani_lessons.py
index a104486..7d38df0 100644
--- a/personal_data/fetchers/wanikani_lessons.py
+++ b/personal_data/fetchers/wanikani_lessons.py
@@ -1,50 +1,55 @@
+import dataclasses
 import datetime
 import logging
+from collections.abc import Iterator, Mapping
+
 import requests
-import dataclasses
-from typing import Iterator, Mapping
+
 # Import the base Scraper class; adjust the import if your code structure differs.
 from personal_data.data import Scraper
 
 logger = logging.getLogger(__name__)
 
+
 @dataclasses.dataclass(frozen=True)
 class WaniKaniLessonsFetcher(Scraper):
     api_token: str
 
     @staticmethod
     def dataset_name() -> str:
-        return "wanikani_lessons"
+        return 'wanikani_lessons'
 
     def scrape(self) -> Iterator[Mapping[str, object]]:
         """
         Fetch assignments from the WaniKani API and yield a dict for each assignment
         with a non-null unlocked_at timestamp.
         """
-        url = "https://api.wanikani.com/v2/assignments"
+        url = 'https://api.wanikani.com/v2/assignments'
         headers = {
-            "Authorization": f"Bearer {self.api_token}",
-            "Wanikani-Revision": "20170710"
+            'Authorization': f'Bearer {self.api_token}',
+            'Wanikani-Revision': '20170710',
         }
         response = requests.get(url, headers=headers)
         if response.status_code != 200:
-            logger.error("Error retrieving assignments: %s", response.text)
+            logger.error('Error retrieving assignments: %s', response.text)
             return
         data = response.json()
         # Check that 'data' key exists in the JSON response.
-        assignments = data.get("data", [])
+        assignments = data.get('data', [])
         for assignment in assignments:
-            assignment_data = assignment.get("data", {})
+            assignment_data = assignment.get('data', {})
             # Only yield if unlocked_at is available.
-            unlocked_at = assignment_data.get("unlocked_at")
+            unlocked_at = assignment_data.get('unlocked_at')
             if unlocked_at:
                 # Convert unlocked_at ISO8601 string (assume 'Z' for UTC) to a datetime object.
                 try:
-                    dt = datetime.datetime.fromisoformat(unlocked_at.replace("Z", "+00:00"))
+                    dt = datetime.datetime.fromisoformat(
+                        unlocked_at.replace('Z', '+00:00'),
+                    )
                 except Exception as e:
                     logger.error("Error parsing unlocked_at '%s': %s", unlocked_at, e)
                     continue
                 yield {
-                    "subject_id": assignment_data.get("subject_id"),
-                    "unlocked_at": dt
+                    'subject_id': assignment_data.get('subject_id'),
+                    'unlocked_at': dt,
                 }