diff --git a/abogen/book_handler.py b/abogen/book_handler.py
index 8f920ae..975bcb8 100644
--- a/abogen/book_handler.py
+++ b/abogen/book_handler.py
@@ -325,7 +325,7 @@ class HandlerDialog(QDialog):
                 )
 
         # 3. If still no nav_item, check for NCX or fallback to NAV HTML in all ITEM_DOCUMENTs
-        ncx_constant = getattr(epub, 'ITEM_NCX', None)
+        ncx_constant = getattr(epub, "ITEM_NCX", None)
         if not nav_item and ncx_constant is not None:
             ncx_items = list(self.book.get_items_of_type(ncx_constant))
             if ncx_items:
@@ -337,13 +337,15 @@ class HandlerDialog(QDialog):
             for item in self.book.get_items_of_type(ebooklib.ITEM_DOCUMENT):
                 try:
                     html_content = item.get_content().decode("utf-8", errors="ignore")
-                    if '<nav' in html_content and 'epub:type="toc"' in html_content:
+                    if "<nav" in html_content and 'epub:type="toc"' in html_content:
                         soup = BeautifulSoup(html_content, "html.parser")
                         nav_tag = soup.find("nav", attrs={"epub:type": "toc"})
                         if nav_tag:
                             nav_item = item
                             nav_type = "html"
-                            logging.info(f"Found NAV HTML with TOC in: {item.get_name()}")
+                            logging.info(
+                                f"Found NAV HTML with TOC in: {item.get_name()}"
+                            )
                             break
                 except Exception as e:
                     continue
@@ -533,7 +535,9 @@ class HandlerDialog(QDialog):
                     pass
             # Fallback: if slice_html is empty, try to get the whole file's text
             if not slice_html.strip() and current_doc_html:
-                logging.warning(f"No content found for src '{current_src}', using full file as fallback.")
+                logging.warning(
+                    f"No content found for src '{current_src}', using full file as fallback."
+                )
                 slice_html = current_doc_html
             if slice_html.strip():
                 slice_soup = BeautifulSoup(slice_html, "html.parser")
@@ -637,7 +641,9 @@ class HandlerDialog(QDialog):
 
         if src:
             base_href, fragment = src.split("#", 1) if "#" in src else (src, None)
-            doc_key, doc_idx = self._find_doc_key(base_href, doc_order, doc_order_decoded)
+            doc_key, doc_idx = self._find_doc_key(
+                base_href, doc_order, doc_order_decoded
+            )
             if not doc_key:
                 logging.warning(
                     f"Navigation entry '{title}' points to '{base_href}', which is not in the spine or document list (even after basename fallback)."
@@ -724,7 +730,9 @@ class HandlerDialog(QDialog):
         fragment = None
         if src:
             base_href, fragment = src.split("#", 1) if "#" in src else (src, None)
-            doc_key, doc_idx = self._find_doc_key(base_href, doc_order, doc_order_decoded)
+            doc_key, doc_idx = self._find_doc_key(
+                base_href, doc_order, doc_order_decoded
+            )
             if doc_key is not None:
                 position = find_position_func(doc_key, fragment)
                 entry_data = {
diff --git a/abogen/conversion.py b/abogen/conversion.py
index 6a226ea..1d3d645 100644
--- a/abogen/conversion.py
+++ b/abogen/conversion.py
@@ -434,8 +434,8 @@ class ConversionThread(QThread):
                 )
                 # Only check for files with allowed extensions (extension without dot, case-insensitive)
                 clash = any(
-                    os.path.splitext(fname)[0] == f"{base_name}{suffix}" and
-                    os.path.splitext(fname)[1][1:].lower() in allowed_exts
+                    os.path.splitext(fname)[0] == f"{base_name}{suffix}"
+                    and os.path.splitext(fname)[1][1:].lower() in allowed_exts
                     for fname in os.listdir(parent_dir)
                 )
                 if not os.path.exists(chapters_out_dir_candidate) and not clash:
@@ -485,8 +485,8 @@ class ConversionThread(QThread):
                     merged_out_file = None
                     ffmpeg_proc = None
                     metadata_options = (
-                            self._extract_and_add_metadata_tags_to_ffmpeg_cmd()
-                        )
+                        self._extract_and_add_metadata_tags_to_ffmpeg_cmd()
+                    )
                     # Prepare ffmpeg command for m4b output
                     cmd = [
                         "ffmpeg",
@@ -680,7 +680,9 @@ class ConversionThread(QThread):
                         continue
                     # Open chapter subtitle file for incremental writing if needed
                     chapter_subtitle_file = None
-                    chapter_srt_index = 1  # Initialize SRT numbering for this chapter file
+                    chapter_srt_index = (
+                        1  # Initialize SRT numbering for this chapter file
+                    )
                     if self.subtitle_mode != "Disabled":
                         subtitle_format = getattr(self, "subtitle_format", "srt")
                         file_extension = "ass" if "ass" in subtitle_format else "srt"
diff --git a/abogen/main.py b/abogen/main.py
index 21e9db5..79ac6fb 100644
--- a/abogen/main.py
+++ b/abogen/main.py
@@ -32,11 +32,13 @@ os.environ["MIOPEN_CONV_PRECISE_ROCM_TUNING"] = "0"
 # Reset sleep states
 atexit.register(prevent_sleep_end)
 
+
 # Also handle signals (Ctrl+C, kill, etc.)
 def _cleanup_sleep(signum, frame):
     prevent_sleep_end()
     sys.exit(0)
 
+
 signal.signal(signal.SIGINT, _cleanup_sleep)
 signal.signal(signal.SIGTERM, _cleanup_sleep)
 
@@ -50,6 +52,7 @@ if sys.stderr is None:
 if platform.system() == "Darwin" and platform.processor() == "arm":
     os.environ["PYTORCH_ENABLE_MPS_FALLBACK"] = "1"
 
+
 # Custom message handler to filter out specific Qt warnings
 def qt_message_handler(mode, context, message):
     if "Wayland does not support QWindow::requestActivate()" in message:
diff --git a/abogen/utils.py b/abogen/utils.py
index 716f8b6..27c8833 100644
--- a/abogen/utils.py
+++ b/abogen/utils.py
@@ -74,24 +74,32 @@ def get_user_config_path():
         if os.path.exists(custom_dir):
             config_dir = custom_dir
         else:
-            config_dir = user_config_dir("abogen", appauthor=False, roaming=True, ensure_exists=True)
+            config_dir = user_config_dir(
+                "abogen", appauthor=False, roaming=True, ensure_exists=True
+            )
     else:
         # Windows and fallback case
-        config_dir = user_config_dir("abogen", appauthor=False, roaming=True, ensure_exists=True)
+        config_dir = user_config_dir(
+            "abogen", appauthor=False, roaming=True, ensure_exists=True
+        )
 
     return os.path.join(config_dir, "config.json")
 
+
 # Define cache path
 def get_user_cache_path(folder=None):
     from platformdirs import user_cache_dir
 
-    cache_dir = user_cache_dir("abogen", appauthor=False, opinion=True, ensure_exists=True)
+    cache_dir = user_cache_dir(
+        "abogen", appauthor=False, opinion=True, ensure_exists=True
+    )
     if folder:
         cache_dir = os.path.join(cache_dir, folder)
         # Ensure the directory exists
         os.makedirs(cache_dir, exist_ok=True)
     return cache_dir
 
+
 _sleep_procs = {"Darwin": None, "Linux": None}  # Store sleep prevention processes