--set-formats argument on CLI

Simpler to use than the --update-metadata method #141

HISTORY.rst

@@ -9,6 +9,7 @@ Release History
 **Improvements**
 
 - Jupytext command line has more arguments: ``--paired-paths`` to list the paths for the paired representations of the notebook, and ``--sync`` to synchronise the content of all paired paths based on the most recent file (#146). In addition, the ``--from`` argument is optional even when the notebook is read from stdin (#148).
+- The pairing information, and more generally the notebook metadata can be edited with the CLL, see the ``--set-formats`` and the ``--update-metadata`` arguments (#141).
 - Format specification allow prefix and suffix for path and file name (#138, #142). Use ``ipynb,prefix/suffix.py:percent`` to pair the current notebook named ``notebook.ipynb`` to a script named ``prefixnotebooksuffix.py``. Suffix and prefix can also be configured on the ``ipynb`` file, with the same syntax.
 - Introducing a new ``hydrogen`` format for scripts, which derives from ``percent``. In that format Jupyter magic commands are not commented (#59, #126, #132).
 - Python scripts or Markdown documents that have no Jupyter metadata receive a metadata filter that ensures that metadata is not exported back to the text representation (#124).

README.md

@@ -165,6 +165,8 @@ jupytext --to md --output - notebook.ipynb      # display the markdown version o
 jupytext --from ipynb --to py:percent           # read ipynb from stdin and write double percent script on stdout
 ```
 
+The `jupytext` command accepts many arguments. Execute `jupytext --help` to access the documentation. For instance, use the `--set-formats` and the `--update-metadata` arguments to edit the pairing information or more generally the notebook metadata.
+
 Jupytext is also available as a Git pre-commit hook. Use this if you want Jupytext to create and update the `.py` (or `.md`...) representation of the staged `.ipynb` notebooks. All you need is to create an executable `.git/hooks/pre-commit` file with the following content:
 ```bash
 #!/bin/sh

jupytext/cli.py

@@ -103,12 +103,7 @@ def convert_notebook_files(nb_files, fmt, input_format=None, output=None, pre_co
             continue
 
         if update_metadata:
-            try:
-                updated_metadata = json.loads(update_metadata)
-            except ValueError as exception:
-                raise ValueError("Could not parse --update-metadata {}. JSONDecodeError: {}".
-                                 format(update_metadata, str(exception)))
-            recursive_update(notebook.metadata, updated_metadata)
+            recursive_update(notebook.metadata, update_metadata)
 
         if comment_magics is not None:
             notebook.metadata.setdefault('jupytext', {})['comment_magics'] = comment_magics
@@ -271,8 +266,13 @@ def cli_jupytext(args=None):
                         nargs='?',
                         default=None,
                         help='Should Jupyter magic commands be commented? (Y)es/(T)rue/(N)o/(F)alse/(D)efault')
+    parser.add_argument('--set-formats',
+                        type=str,
+                        help='Set jupytext.formats metadata to the given value. Use this to activate pairing on a '
+                             'notebook, with e.g. --set-formats ipynb,py:light')
     parser.add_argument('--update-metadata',
-                        default=None,
+                        default={},
+                        type=json.loads,
                         help='Update the notebook metadata with the desired dictionary. Argument must be given in JSON '
                              'format. For instance, if you want to activate a pairing in the generated file, '
                              """use e.g. '{"jupytext":{"formats":"ipynb,py:light"}}'""")
@@ -292,6 +292,9 @@ def cli_jupytext(args=None):
     if args.version:
         return args
 
+    if args.set_formats:
+        args.update_metadata = recursive_update(args.update_metadata, {'jupytext': {'formats': args.set_formats}})
+
     if args.input_format:
         args.input_format = canonize_format(args.input_format)
         if not args.notebooks and not args.output:

tests/test_cli.py

@@ -366,6 +366,19 @@ def hook():
     assert not os.path.isfile(tmp_py)
 
 
+@pytest.mark.parametrize('py_file', list_notebooks('python'))
+def test_set_formats(py_file, tmpdir):
+    tmp_py = str(tmpdir.join('notebook.py'))
+    tmp_ipynb = str(tmpdir.join('notebook.ipynb'))
+
+    copyfile(py_file, tmp_py)
+
+    jupytext(['--to', 'ipynb', tmp_py, '--set-formats', 'ipynb,py:light'])
+
+    nb = readf(tmp_ipynb)
+    assert nb.metadata['jupytext']['formats'] == 'ipynb,py:light'
+
+
 @pytest.mark.parametrize('py_file', list_notebooks('python'))
 def test_update_metadata(py_file, tmpdir, capsys):
     tmp_py = str(tmpdir.join('notebook.py'))
@@ -388,7 +401,7 @@ def test_update_metadata(py_file, tmpdir, capsys):
         jupytext(['--to', 'ipynb', tmp_py, '--update-metadata', '{"incorrect": "JSON"'])
 
     out, err = capsys.readouterr()
-    assert 'JSONDecodeError' in err
+    assert 'invalid' in err
 
 
 @pytest.mark.parametrize('nb_file', list_notebooks('ipynb_py'))