first attempt for fix_dir_mtime.py, plus some minor changes

.gitignore

@@ -0,0 +1,13 @@
+# Python
+__pycache__/
+*.pyc
+*.pyo
+*.pyd
+.pytest_cache/
+
+# Editors / OS
+.DS_Store
+
+# Optional: local scratch
+*.tmp
+*.swp

fix_dir_mtime.py

@@ -0,0 +1,34 @@
+#!/usr/bin/env python3
+
+import os
+import sys
+from pathlib import Path
+
+
+def update_dir_mtime(path: Path):
+    if not path.is_dir():
+        return path.stat().st_mtime
+
+    newest = 0
+
+    for child in path.iterdir():
+        if child.is_dir():
+            child_mtime = update_dir_mtime(child)
+        else:
+            child_mtime = child.stat().st_mtime
+
+        newest = max(newest, child_mtime)
+
+    if newest > 0:
+        os.utime(path, (newest, newest))
+
+    return max(newest, path.stat().st_mtime)
+
+
+if __name__ == "__main__":
+    if len(sys.argv) != 2:
+        print("Usage: fix_dir_mtime.py <directory>")
+        sys.exit(1)
+
+    root = Path(sys.argv[1]).resolve()
+    update_dir_mtime(root)