Update the timestamp of the py file only (#1227)

if it is older than that of the nb file

CHANGELOG.md

@@ -12,6 +12,7 @@ Jupytext ChangeLog
 - Temporary text notebooks for the `--pipe` or `--check` commands are now created in the notebook directory ([#1206](https://github.com/mwouts/jupytext/issues/1206))
 - Jupytext uses the standard library `tomllib` in Python 3.11, or `tomli` in Python 3.10 or older, to match JupyterLab's dependencies ([#1195](https://github.com/mwouts/jupytext/issues/1195))
 - The dependencies of the JupyterLab extension were updated ([#1216](https://github.com/mwouts/jupytext/issues/1216), [#1218](https://github.com/mwouts/jupytext/issues/1218), [#1231](https://github.com/mwouts/jupytext/issues/1231))
+- `jupytext --sync` will not update the timestamp of text notebooks if their content is unchanged ([#1215](https://github.com/mwouts/jupytext/issues/1215))
 
 
 **Fixed**

src/jupytext/cli.py

@@ -858,9 +858,18 @@ def lazy_write(path, fmt=None, action=None, update_timestamp_only=False):
                 f"[jupytext] Setting the timestamp of {shlex.quote(path)} equal to that of {shlex.quote(nb_file)}"
             )
             os.utime(path, (os.stat(path).st_atime, os.stat(nb_file).st_mtime))
-        elif not modified and not path.endswith(".ipynb"):
-            log(f"[jupytext] Updating the timestamp of {shlex.quote(path)}")
-            os.utime(path, None)
+        elif not modified:
+            if path.endswith(".ipynb"):
+                # No need to update the timestamp of ipynb files
+                log(f"[jupytext] Unchanged {shlex.quote(path)}")
+            elif args.sync:
+                # if the content is unchanged (and matches ipynb), we don't need
+                # to update the timestamp as the contents manager will not throw in
+                # that case (see the try/catch on read_pair(... must_match=True))
+                log(f"[jupytext] Unchanged {shlex.quote(path)}")
+            else:
+                log(f"[jupytext] Updating the timestamp of {shlex.quote(path)}")
+                os.utime(path, None)
 
         if args.pre_commit:
             system("git", "add", path)