Document why bytes filenames matter

audreyfeldroy · audreyfeldroy · commit c375996242da · 2026-03-09T00:15:06.000+08:00
CJK locales on Windows produce Shift-JIS, GBK, or EUC-KR filenames
that aren't valid UTF-8. When those files land on Linux (or Docker,
or WSL), os.listdir() returns bytes. The comment records the use
case so future readers don't remove the bytes handling.
diff --git a/src/binaryornot/helpers.py b/src/binaryornot/helpers.py
@@ -59,6 +59,9 @@ def has_binary_extension(filename: str | bytes | Path) -> bool:
     :param filename: File path to check.
     :returns: True if the extension is in the known binary list.
     """
+    # bytes filenames matter for CJK locales (Shift-JIS, GBK, EUC-KR):
+    # files created on Windows with a CJK locale produce non-UTF-8 names
+    # that os.listdir() returns as bytes on Linux/Docker/WSL.
     if isinstance(filename, bytes):
         filename = os.fsdecode(filename)
     p = Path(filename) if not isinstance(filename, Path) else filename
