Remove output metadata in ClearOutputPreprocessor.

.travis.yml

@@ -29,6 +29,7 @@ before_install:
     - git clone --quiet --depth 1 https://github.com/minrk/travis-wheels travis-wheels
 install:
     - wget https://github.com/jgm/pandoc/releases/download/1.19.1/pandoc-1.19.1-1-amd64.deb && sudo dpkg -i pandoc-1.19.1-1-amd64.deb
+    - pip install --upgrade setuptools pip
     - pip install -f travis-wheels/wheelhouse . codecov coverage
     - pip install nbconvert[execute,serve,test]
     - python -m ipykernel.kernelspec --user

nbconvert/preprocessors/clearoutput.py

@@ -3,18 +3,27 @@
 # Copyright (c) IPython Development Team.
 # Distributed under the terms of the Modified BSD License.
 
+from traitlets import Set
 from .base import Preprocessor
 
 class ClearOutputPreprocessor(Preprocessor):
     """
     Removes the output from all code cells in a notebook.
     """
 
+    remove_metadata_fields = Set(
+        {'collapsed', 'scrolled'}
+    ).tag(config=True)
+
     def preprocess_cell(self, cell, resources, cell_index):
         """
         Apply a transformation on each cell. See base.py for details.
         """
         if cell.cell_type == 'code':
             cell.outputs = []
             cell.execution_count = None
+            # Remove metadata associated with output
+            if 'metadata' in cell:
+                for field in self.remove_metadata_fields:
+                    cell.metadata.pop(field, None)
         return cell, resources

nbconvert/preprocessors/tests/test_clearoutput.py

@@ -12,6 +12,13 @@
 class TestClearOutput(PreprocessorTestsBase):
     """Contains test functions for clearoutput.py"""
 
+    def build_notebook(self):
+        notebook = super(TestClearOutput, self).build_notebook()
+        # Add a test field to the first cell
+        if 'metadata' not in notebook.cells[0]:
+            notebook.cells[0].metadata = {}
+        notebook.cells[0].metadata['test_field'] = 'test_value'
+        return notebook
 
     def build_preprocessor(self):
         """Make an instance of a preprocessor"""
@@ -25,9 +32,18 @@ def test_constructor(self):
 
     def test_output(self):
         """Test the output of the ClearOutputPreprocessor"""
-        nb = self.build_notebook()
-        res = self.build_resources()
-        preprocessor = self.build_preprocessor()
-        nb, res = preprocessor(nb, res)
-        assert nb.cells[0].outputs == []
-        assert nb.cells[0].execution_count is None
+        for remove_test_field in [False, True]:
+            nb = self.build_notebook()
+            res = self.build_resources()
+            preprocessor = self.build_preprocessor()
+            # Also remove the test field in addition to defaults
+            if remove_test_field:
+                preprocessor.remove_metadata_fields.add('test_field')
+            nb, res = preprocessor(nb, res)
+            assert nb.cells[0].outputs == []
+            assert nb.cells[0].execution_count is None
+            if 'metadata' in nb.cells[0]:
+                for field in preprocessor.remove_metadata_fields:
+                    assert field not in nb.cells[0].metadata
+                # Ensure the test field is only removed when added to the traitlet
+                assert remove_test_field or 'test_field' in nb.cells[0].metadata