Jupytext CLI updates the timestamp of the input file

To allow paired notebooks to be opened in Jupyter later on.
Closes #254 #335

jupytext/cli.py

@@ -411,6 +411,11 @@ def jupytext_single_file(nb_file, args, log):
                 write(notebook, alt_path, fmt=alt_fmt)
                 if args.pre_commit:
                     system('git', 'add', alt_path)
+    elif os.path.isfile(nb_file) and nb_dest.endswith('.ipynb') and not nb_file.endswith('.ipynb'):
+        # Update the original text file timestamp, as required by our Content Manager
+        # Otherwise Jupyter will refuse to open the paired notebook #335
+        log("[jupytext] Sync timestamp of '{}'".format(nb_file))
+        os.utime(nb_file)
 
     return 0
 

tests/test_contentsmanager.py

@@ -10,6 +10,7 @@
 from tornado.web import HTTPError
 from jupytext.compare import compare
 import jupytext
+from jupytext.cli import jupytext as jupytext_cli
 from jupytext.jupytext import writes, write, read
 from jupytext.compare import compare_notebooks
 from jupytext.header import header_to_metadata_and_cell
@@ -430,6 +431,34 @@ def test_outdated_text_notebook(nb_file, tmpdir):
     cm.get(tmp_nbpy)
 
 
+@pytest.mark.parametrize('nb_file', list_notebooks('ipynb_py')[:1])
+def test_reload_notebook_after_jupytext_cli(nb_file, tmpdir):
+    tmp_ipynb = str(tmpdir.join('notebook.ipynb'))
+    tmp_nbpy = str(tmpdir.join('notebook.py'))
+
+    cm = jupytext.TextFileContentsManager()
+    cm.default_jupytext_formats = 'py,ipynb'
+    cm.outdated_text_notebook_margin = 0
+    cm.root_dir = str(tmpdir)
+
+    # write the paired notebook
+    nb = jupytext.read(nb_file)
+    cm.save(model=dict(type='notebook', content=nb), path='notebook.py')
+
+    assert os.path.isfile(tmp_ipynb)
+    assert os.path.isfile(tmp_nbpy)
+
+    # run jupytext CLI
+    jupytext_cli([tmp_nbpy, '--to', 'ipynb', '--update'])
+
+    # test reload
+    nb1 = cm.get('notebook.py')['content']
+    nb2 = cm.get('notebook.ipynb')['content']
+
+    compare_notebooks(nb1, nb)
+    compare_notebooks(nb2, nb)
+
+
 @skip_if_dict_is_not_ordered
 @pytest.mark.parametrize('nb_file', list_notebooks('percent'))
 def test_load_save_percent_format(nb_file, tmpdir):