Set prompt number to None

IPython/nbconvert/preprocessors/clearoutput.py

@@ -1,29 +1,28 b''
 """Module containing a preprocessor that removes the outputs from code cells"""
 
 # Copyright (c) IPython Development Team.
 # Distributed under the terms of the Modified BSD License.
 
 #-----------------------------------------------------------------------------
 # Imports
 #-----------------------------------------------------------------------------
 
 from .base import Preprocessor
 
 
 #-----------------------------------------------------------------------------
 # Classes
 #-----------------------------------------------------------------------------
 class ClearOutputPreprocessor(Preprocessor):
     """
     Removes the output from all code cells in a notebook.
     """
 
     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 = []
-            if 'prompt_number' in cell:
-                del cell['prompt_number']
+            cell['prompt_number'] = None
         return cell, resources

IPython/nbconvert/preprocessors/tests/test_clearoutput.py

@@ -1,42 +1,42 b''
 """
 Module with tests for the clearoutput preprocessor.
 """
 
 # Copyright (c) IPython Development Team.
 # Distributed under the terms of the Modified BSD License.
 
 #-----------------------------------------------------------------------------
 # Imports
 #-----------------------------------------------------------------------------
 from IPython.nbformat import current as nbformat
 
 from .base import PreprocessorTestsBase
 from ..clearoutput import ClearOutputPreprocessor
 
 
 #-----------------------------------------------------------------------------
 # Class
 #-----------------------------------------------------------------------------
 
 class TestClearOutput(PreprocessorTestsBase):
     """Contains test functions for clearoutput.py"""
 
 
     def build_preprocessor(self):
         """Make an instance of a preprocessor"""
         preprocessor = ClearOutputPreprocessor()
         preprocessor.enabled = True
         return preprocessor
 
     def test_constructor(self):
         """Can a ClearOutputPreprocessor be constructed?"""
         self.build_preprocessor()
 
     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.worksheets[0].cells[0].outputs == []
-        assert 'prompt_number' not in nb.worksheets[0].cells[0]
+        assert nb.worksheets[0].cells[0].prompt_number is None