Fix active cells in the py:percent format

CHANGELOG.md

@@ -13,6 +13,7 @@
 - Fixed the CLI example for not commenting out magic commands: `--opt comment_magics=false`. In addition, most of the `jupytext` commands in `using-cli.md` are now tested! (#465)
 - `jupytext.read` and `jupytext.write` now give more meaningful errors when the format information is incorrect (#462)
 - Multiline comments starting with quadruple quotes should not cause issues anymore (#460)
+- Fixed active cells in the py:percent format (#477)
 
 1.4.1 (2020-03-19)
 ------------------

jupytext/cell_reader.py

@@ -689,6 +689,10 @@ def find_cell_end(self, lines):
 
         if self.metadata and 'cell_type' in self.metadata:
             self.cell_type = self.metadata.pop('cell_type')
+        elif not is_active('.ipynb', self.metadata):
+            if self.metadata.get('active') == '':
+                del self.metadata['active']
+            self.cell_type = 'raw'
         else:
             self.cell_type = 'code'
 

jupytext/cell_to_text.py

@@ -377,20 +377,20 @@ def __init__(self, *args, **kwargs):
 
     def cell_to_text(self):
         """Return the text representation for the cell"""
-        if self.cell_type != 'code':
-            self.metadata['cell_type'] = self.cell_type
-
         active = is_active(self.ext, self.metadata, same_language(self.language, self.default_language))
         if self.cell_type == 'raw' and 'active' in self.metadata and self.metadata['active'] == '':
             del self.metadata['active']
 
+        if not self.is_code():
+            self.metadata['cell_type'] = self.cell_type
+
         options = metadata_to_double_percent_options(self.metadata, self.cell_metadata_json)
         if options.startswith('%') or not options:
             lines = [self.comment + ' %%' + options]
         else:
             lines = [self.comment + ' %% ' + options]
 
-        if self.cell_type == 'code' and active:
+        if self.is_code() and active:
             source = copy(self.source)
             comment_magic(source, self.language, self.comment_magics)
             if source == ['']:

tests/test_active_cells.py

@@ -243,3 +243,43 @@ def test_active_rmd(ext, no_jupytext_version_number):
 @pytest.mark.parametrize('ext', ['.Rmd', '.py', '.R'])
 def test_active_not_include_rmd(ext, no_jupytext_version_number):
     check_active_cell(ext, ACTIVE_NOT_INCLUDE_RMD)
+
+
+def test_active_cells_from_py_percent(text="""# %% active="py"
+print('should only be displayed in py file')
+
+# %% tags=["active-py"]
+print('should only be displayed in py file')
+
+# %% active="ipynb"
+# print('only in jupyter')
+"""):
+    """Example taken from https://github.com/mwouts/jupytext/issues/477"""
+    nb = jupytext.reads(text, 'py:percent')
+    assert nb.cells[0].cell_type == 'raw'
+    assert nb.cells[1].cell_type == 'raw'
+    assert nb.cells[2].cell_type == 'code'
+    assert nb.cells[2].source == "print('only in jupyter')"
+
+    text2 = jupytext.writes(nb, 'py:percent')
+    compare(text2, text)
+
+
+def test_active_cells_from_py_light(text="""# + active="py"
+print('should only be displayed in py file')
+
+# + tags=["active-py"]
+print('should only be displayed in py file')
+
+# + active="ipynb"
+# print('only in jupyter')
+"""):
+    """Example adapted from https://github.com/mwouts/jupytext/issues/477"""
+    nb = jupytext.reads(text, 'py')
+    assert nb.cells[0].cell_type == 'raw'
+    assert nb.cells[1].cell_type == 'raw'
+    assert nb.cells[2].cell_type == 'code'
+    assert nb.cells[2].source == "print('only in jupyter')"
+
+    text2 = jupytext.writes(nb, 'py')
+    compare(text2, text)