Introducing the bare format

Fixes #152

HISTORY.rst

@@ -12,6 +12,7 @@ Release History
 - 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).
+- Introducing a new ``bare`` format for scripts, which derives from ``light``. That format has no cell marker. Use a notebook metadata filter ``{"jupytext": {"notebook_metadata_filter":"-all"}}`` if you want no YAML header (#152).
 - 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).
 - Metadata filters are represented as strings rather than dictionaries to make YAML headers shorter. Previous syntax from #105 is still supported. They were also renamed to ``notebook_metadata_filter`` and ``cell_metadata_filter``.
 - Markdown and RMarkdown formats have a new option ``split_at_heading`` to split Markdown cells at heading (#130)

README.md

@@ -247,6 +247,8 @@ The `light` format has:
 
 The `light` format is currently available for Python, Julia, R, Bash, Scheme and C++. Open our sample notebook in the `light` format [here](https://github.com/mwouts/jupytext/blob/master/demo/World%20population.lgt.py).
 
+A variation of the `light` format is the `bare` format, with no cell marker at all. Please note that this format will split your code cells on code paragraphs. By default, this format still includes a YAML header - if you prefer to also remove the header, set `"notebook_metadata_filter": "-all"` in the jupytext section of your notebook metadata.  
+
 ### The `percent` format
 
 The `percent` format is a representation of Jupyter notebooks as scripts, in which cells are delimited with a commented double percent sign `# %%`. The format was introduced by Spyder five years ago, and is now supported by many editors, including

jupytext/cell_to_text.py

@@ -167,6 +167,7 @@ def endofcell_marker(source, comment):
 class LightScriptCellExporter(BaseCellExporter):
     """A class that represent a notebook cell as a Python or Julia script"""
     default_comment_magics = True
+    use_cell_markers = True
 
     def __init__(self, *args, **kwargs):
         BaseCellExporter.__init__(self, *args, **kwargs)
@@ -199,7 +200,7 @@ def code_to_text(self):
         if self.explicit_start_marker(source):
             self.metadata['endofcell'] = endofcell_marker(source, self.comment)
 
-        if not self.metadata:
+        if not self.metadata or not self.use_cell_markers:
             return source
 
         lines = []
@@ -215,6 +216,8 @@ def code_to_text(self):
     def explicit_start_marker(self, source):
         """Does the python representation of this cell requires an explicit
         start of cell marker?"""
+        if not self.use_cell_markers:
+            return False
         if self.metadata:
             return True
         if all([line.startswith(self.comment) for line in self.source]):
@@ -242,6 +245,11 @@ def simplify_code_markers(self, text, next_text, lines):
         return text
 
 
+class BareScriptCellExporter(LightScriptCellExporter):
+    """A class that writes notebook cells as scripts with no cell markers"""
+    use_cell_markers = False
+
+
 class RScriptCellExporter(BaseCellExporter):
     """A class that can represent a notebook cell as a R script"""
     default_comment_magics = True

jupytext/formats.py

@@ -11,7 +11,7 @@
     LightScriptCellReader, RScriptCellReader, DoublePercentScriptCellReader, HydrogenCellReader, \
     SphinxGalleryScriptCellReader
 from .cell_to_text import MarkdownCellExporter, RMarkdownCellExporter, \
-    LightScriptCellExporter, RScriptCellExporter, DoublePercentCellExporter, \
+    LightScriptCellExporter, BareScriptCellExporter, RScriptCellExporter, DoublePercentCellExporter, \
     HydrogenCellExporter, SphinxGalleryCellExporter
 from .cell_metadata import _JUPYTEXT_CELL_METADATA
 from .stringparser import StringParser
@@ -87,6 +87,15 @@ def __init__(self,
             # Version 1.0 on 2018-08-22 - jupytext v0.5.2 : Initial version
             current_version_number='1.3',
             min_readable_version_number='1.1') for ext in _SCRIPT_EXTENSIONS] + \
+    [
+        NotebookFormatDescription(
+            format_name='bare',
+            extension=ext,
+            header_prefix=_SCRIPT_EXTENSIONS[ext]['comment'],
+            cell_reader_class=LightScriptCellReader,
+            cell_exporter_class=BareScriptCellExporter,
+            current_version_number='1.0',
+            min_readable_version_number='1.0') for ext in _SCRIPT_EXTENSIONS] + \
     [
         NotebookFormatDescription(
             format_name='percent',

tests/test_read_simple_bare.py

@@ -0,0 +1,31 @@
+from nbformat.v4.nbbase import new_notebook, new_code_cell, new_markdown_cell
+from testfixtures import compare
+from jupytext import reads, writes
+from jupytext.combine import combine_inputs_with_outputs
+
+
+def test_write_reload_simple_notebook():
+    nb1 = new_notebook(cells=[
+        new_markdown_cell('A markdown cell', metadata={'md': 'value'}),
+        new_code_cell('1 + 1'),
+        new_markdown_cell('A markdown cell', metadata={'md': 'value'}),
+        new_code_cell("""def f(x):
+    return x""", metadata={'md': 'value'}),
+        new_markdown_cell('A markdown cell', metadata={'md': 'value'}),
+        new_code_cell("""def g(x):
+    return x
+
+
+def h(x):
+    return x
+""", metadata={'md': 'value'})])
+
+    text = writes(nb1, 'py:bare')
+    nb2 = reads(text, 'py:bare')
+    combine_inputs_with_outputs(nb2, nb1, 'py:bare')
+    nb2.metadata.pop('jupytext')
+
+    assert len(nb2.cells) == 7
+    nb1.cells = nb1.cells[:5]
+    nb2.cells = nb2.cells[:5]
+    compare(nb1, nb2)