Last modified timestamp of a paired notebook is that of the file last…

… written

Fix #207

jupytext/contentsmanager.py

@@ -237,6 +237,7 @@ def save(self, model, path=''):
 
             # Save as ipynb first
             return_value = None
+            value = None
             for fmt in jupytext_formats[::-1]:
                 if fmt['extension'] != '.ipynb':
                     continue
@@ -267,6 +268,8 @@ def save(self, model, path=''):
                     if alt_path == path:
                         return_value = value
 
+            # Update modified timestamp to match that of the pair #207
+            return_value['last_modified'] = value['last_modified']
             return return_value
 
         except Exception as err:

tests/test_contentsmanager.py

@@ -1121,7 +1121,7 @@ def test_share_py_recreate_ipynb(tmpdir, nb_file):
     cm.default_cell_metadata_filter = "-all"
 
     nb = readf(nb_file)
-    cm.save(model=dict(content=nb, type='notebook'), path='nb.ipynb')
+    model_ipynb = cm.save(model=dict(content=nb, type='notebook'), path='nb.ipynb')
 
     assert os.path.isfile(tmp_ipynb)
     assert os.path.isfile(tmp_py)
@@ -1134,3 +1134,6 @@ def test_share_py_recreate_ipynb(tmpdir, nb_file):
 
     # ipynb is re-created
     assert os.path.isfile(tmp_ipynb)
+
+    # save time of ipynb is that of py file
+    assert model_ipynb['last_modified'] == model['last_modified']