diff --git a/libpurple_to_markdown/__main__.py b/libpurple_to_markdown/__main__.py
index cfd7f91..9b3bf95 100644
--- a/libpurple_to_markdown/__main__.py
+++ b/libpurple_to_markdown/__main__.py
@@ -1,9 +1,8 @@
 import argparse
 import dataclasses
-import logging
 import datetime
-from collections.abc import Iterable, Iterator, Mapping
-from typing import Callable
+import logging
+from collections.abc import Callable, Iterable, Iterator, Mapping
 from pathlib import Path
 
 from . import (
@@ -18,7 +17,10 @@ from .markdown import format_messages
 logger = logging.getLogger(__name__)
 
 
-def group_messages(messages: Iterable[Message], key_fn: Callable[[Message], str]) -> dict[str, list[Message]]:
+def group_messages(
+    messages: Iterable[Message],
+    key_fn: Callable[[Message], str],
+) -> dict[str, list[Message]]:
     by_key: dict[str, list[Message]] = {}
     for msg in messages:
         by_key.setdefault(key_fn(msg), []).append(msg)
@@ -48,18 +50,23 @@ MAX_AVERAGE_MESSAGES_PER_PERIOD = 120
 TOO_FEW_MESSAGES_TO_CARE = 2
 
 PERIOD_KEYS_BY_NAME: Mapping[str, Callable[[Message], str]] = {
-        'full': (lambda msg: 'full'),
-        'year': year_period_key,
-        'quarter': year_quarter_period_key,
-        'month': year_and_month_period_key,
+    'full': (lambda msg: 'full'),
+    'year': year_period_key,
+    'quarter': year_quarter_period_key,
+    'month': year_and_month_period_key,
 }
 
 
-def group_messages_by_period(messages: Iterable[Message], period_key: str | None = None) -> tuple[dict[str, list[Message]], Callable[[Message], str]]:
+def group_messages_by_period(
+    messages: Iterable[Message],
+    period_key: str | None = None,
+) -> tuple[dict[str, list[Message]], Callable[[Message], str]]:
     # Determine key function
-    possible_period_keys: Iterable[Callable[[Message], str]] = PERIOD_KEYS_BY_NAME.values()
+    possible_period_keys: Iterable[Callable[[Message], str]] = (
+        PERIOD_KEYS_BY_NAME.values()
+    )
     if period_key is not None:
-        possible_period_keys  = [PERIOD_KEYS_BY_NAME[period_key]]
+        possible_period_keys = [PERIOD_KEYS_BY_NAME[period_key]]
     del period_key
 
     # Group by key
@@ -89,10 +96,19 @@ def parse_args():
     parser.add_argument('--output', type=Path)
     parser.add_argument('--myself', type=str, default='Myself')
     parser.add_argument('--overwrite', action='store_true', dest='overwrite_files')
-    parser.add_argument('--period', dest='period_key', choices=list(PERIOD_KEYS_BY_NAME.keys()))
-    parser.add_argument('--skip-this-period', action='store_true', dest='skip_this_period')
+    parser.add_argument(
+        '--period',
+        dest='period_key',
+        choices=list(PERIOD_KEYS_BY_NAME.keys()),
+    )
+    parser.add_argument(
+        '--skip-this-period',
+        action='store_true',
+        dest='skip_this_period',
+    )
     return parser.parse_args()
 
+
 def main():
     logging.basicConfig()
     logging.getLogger().setLevel('INFO')
@@ -125,7 +141,10 @@ def main():
             logger.info('  "%s": Skipped due to too few messages', chat_id)
             continue
 
-        messages_by_period, period_key_fn = group_messages_by_period(messages_in_chat, args.period_key)
+        messages_by_period, period_key_fn = group_messages_by_period(
+            messages_in_chat,
+            args.period_key,
+        )
         logger.info(
             '  "%s": %d messages, %d periods (%d msg/period avg)',
             chat_id,
@@ -134,7 +153,7 @@ def main():
             len(messages_in_chat_original) / len(messages_by_period),
         )
 
-        this_period_name = period_key_fn(Message(datetime.datetime.now(), '','',''))
+        this_period_name = period_key_fn(Message(datetime.datetime.now(), '', '', ''))
 
         for period_key_name, messages in messages_by_period.items():
             file_escaped_chat_id = chat_id.replace(' ', '-')