Ignore jupytext specific cell metadata

Reproduce and fix #139

jupytext/jupytext.py

@@ -19,8 +19,8 @@
     update_jupytext_formats_metadata, format_name_for_ext, transition_to_jupytext_section_in_metadata
 from .header import header_to_metadata_and_cell, metadata_and_cell_to_header, \
     encoding_and_executable, insert_or_test_version_number
-from .languages import default_language_from_metadata_and_ext, \
-    set_main_and_cell_language
+from .languages import default_language_from_metadata_and_ext, set_main_and_cell_language
+from .cell_metadata import _JUPYTEXT_CELL_METADATA
 
 
 class TextNotebookReader(NotebookReader):
@@ -59,6 +59,7 @@ def reads(self, s, **_):
             lines = lines[pos:]
 
         if self.freeze_metadata and 'metadata_filter' not in metadata.get('jupytext', {}):
+            cell_metadata = [m for m in cell_metadata if m not in _JUPYTEXT_CELL_METADATA]
             metadata.setdefault('jupytext', {})['metadata_filter'] = {
                 'notebook': {'additional': list(metadata.keys()), 'excluded': 'all'},
                 'cells': {'additional': list(cell_metadata), 'excluded': 'all'}}

tests/test_contentsmanager.py

@@ -92,6 +92,33 @@ def test_load_save_rename_nbpy(nb_file, tmpdir):
     assert os.path.isfile(str(tmpdir.join('new.nb.py')))
 
 
+@skip_if_dict_is_not_ordered
+@pytest.mark.parametrize('script', list_notebooks('python', skip='light'))
+def test_load_save_py_freeze_metadata(script, tmpdir):
+    tmp_nbpy = 'notebook.py'
+
+    cm = jupytext.TextFileContentsManager()
+    cm.freeze_metadata = True
+    cm.root_dir = str(tmpdir)
+
+    # read original file
+    with open(script) as fp:
+        text_py = fp.read()
+
+    # write to tmp_nbpy
+    with open(str(tmpdir.join(tmp_nbpy)), 'w') as fp:
+        fp.write(text_py)
+
+    # open and save notebook
+    nb = cm.get(tmp_nbpy)['content']
+    cm.save(model=dict(type='notebook', content=nb), path=tmp_nbpy)
+
+    with open(str(tmpdir.join(tmp_nbpy))) as fp:
+        text_py2 = fp.read()
+
+    compare(text_py, text_py2)
+
+
 @skip_if_dict_is_not_ordered
 @pytest.mark.parametrize('nb_file', list_notebooks('ipynb_py'))
 def test_load_save_rename_notebook_with_dot(nb_file, tmpdir):