only process cr if it's found

because re.sub is crazy slow.

IPython/nbconvert/preprocessors/coalescestreams.py

@@ -1,77 +1,77 b''
 """Preprocessor for merging consecutive stream outputs for easier handling."""
 
 # Copyright (c) IPython Development Team.
 # Distributed under the terms of the Modified BSD License.
 
 import re
 
 def cell_preprocessor(function):
     """
     Wrap a function to be executed on all cells of a notebook
     
     The wrapped function should have these parameters:
     
     cell : NotebookNode cell
         Notebook cell being processed
     resources : dictionary
         Additional resources used in the conversion process.  Allows
         preprocessors to pass variables into the Jinja engine.
     index : int
         Index of the cell being processed
     """
     
     def wrappedfunc(nb, resources):
         from IPython.config import Application
         if Application.initialized():
             Application.instance().log.debug(
                 "Applying preprocessor: %s", function.__name__
             )
         for worksheet in nb.worksheets:
             for index, cell in enumerate(worksheet.cells):
                 worksheet.cells[index], resources = function(cell, resources, index)
         return nb, resources
     return wrappedfunc
 
 cr_pat = re.compile(r'.*\r(?=[^\n])')
 
 @cell_preprocessor
 def coalesce_streams(cell, resources, index):
     """
     Merge consecutive sequences of stream output into single stream
     to prevent extra newlines inserted at flush calls
     
     Parameters
     ----------
     cell : NotebookNode cell
         Notebook cell being processed
     resources : dictionary
         Additional resources used in the conversion process.  Allows
         transformers to pass variables into the Jinja engine.
     index : int
         Index of the cell being processed
     """
     
     outputs = cell.get('outputs', [])
     if not outputs:
         return cell, resources
     
     last = outputs[0]
     new_outputs = [last]
     for output in outputs[1:]:
         if (output.output_type == 'stream' and
             last.output_type == 'stream' and
             last.stream == output.stream
         ):
             last.text += output.text
 
         else:
             new_outputs.append(output)
             last = output
     
     # process \r characters
     for output in new_outputs:
-        if output.output_type == 'stream':
+        if output.output_type == 'stream' and '\r' in output.text:
             output.text = cr_pat.sub('', output.text)
 
     cell.outputs = new_outputs
     return cell, resources