only rewrite utility files if contents changed

scripts/util.py

@@ -1,7 +1,12 @@
 # -*- coding: utf-8 -*-
 
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License version 2 as
+# published by the Free Software Foundation.
+
+import os
+import io
 import sys
-import os.path
 
 ROOTDIR = os.path.dirname(os.path.dirname(os.path.abspath(__file__)))
 sys.path.insert(0, os.path.realpath(ROOTDIR))
@@ -11,3 +16,32 @@ def path(*segments, join=os.path.join):
     result = join(ROOTDIR, *segments)
     os.makedirs(os.path.dirname(result), exist_ok=True)
     return result
+
+
+class lazy():
+
+    def __init__(self, path):
+        self.path = path
+        self.buffer = io.StringIO()
+
+    def __enter__(self):
+        return self.buffer
+
+    def __exit__(self, exc, value, tb):
+        # get content of old file
+        try:
+            with open(self.path, encoding="utf-8") as fp:
+                old = fp.read()
+        except Exception:
+            old = None
+
+        # get new content
+        new = self.buffer.getvalue()
+
+        if new != old:
+            # rewrite entire file
+            with open(self.path, "w", encoding="utf-8") as fp:
+                fp.write(new)
+        else:
+            # only update atime and mtime
+            os.utime(self.path)