Removed inheritance breaking clear-output option

nbconvert/preprocessors/clearoutput.py

@@ -6,6 +6,7 @@
 from traitlets import Set
 from .base import Preprocessor
 
+
 class ClearOutputPreprocessor(Preprocessor):
     """
     Removes the output from all code cells in a notebook.

nbconvert/preprocessors/tagremove.py

@@ -7,10 +7,10 @@
 # Distributed under the terms of the Modified BSD License.
 
 from traitlets import Set, Unicode
-from . import ClearOutputPreprocessor
+from .base import Preprocessor
 
 
-class TagRemovePreprocessor(ClearOutputPreprocessor):
+class TagRemovePreprocessor(Preprocessor):
     """
     Removes inputs, outputs, or cells from a notebook that
     have tags that designate they are to be removed prior to exporting

nbconvert/tests/test_nbconvertapp.py

@@ -6,6 +6,7 @@
 
 import os
 import io
+import nbformat
 
 from .base import TestsBase
 from ..postprocessors import PostProcessorBase
@@ -90,6 +91,20 @@ def test_explicit(self):
             assert not os.path.isfile('notebook1.py')
             assert os.path.isfile('notebook2.py')
 
+    def test_clear_output(self):
+        """
+        Can we clear outputs?
+        """
+        with self.create_temp_cwd(['notebook*.ipynb']) as td:
+            self.nbconvert('--clear-output notebook1')
+            assert os.path.isfile('notebook1.ipynb')
+            with open('notebook1.ipynb', encoding='utf8') as f:
+                nb = nbformat.read(f, 4)
+                for cell in nb.cells:
+                    # Skip markdown cells
+                    if 'outputs' in cell:
+                        assert cell.outputs == []
+
     def test_absolute_template_file(self):
         """--template-file '/path/to/template.tpl'"""
         with self.create_temp_cwd(['notebook*.ipynb']), tempdir.TemporaryDirectory() as td: