Replace ad-hoc/broken code with safe method to extract the prompt_number of a cell.

The helper function returns the converter's blank symbol (' ' for HTML,
space for other converters) if the cell doesn't have a prompt_number.

converters/base.py

@@ -63,6 +63,7 b' class Converter(object):'
     user_preamble = None
     output = unicode()
     raw_as_verbatim = False
+    blank_symbol = " "
 
     def __init__(self, infile):
         self.infile = infile
@@ -79,6 +80,10 b' class Converter(object):'
         if os.path.isdir(self.files_dir) and not os.listdir(self.files_dir):
             os.rmdir(self.files_dir)
 
+    def _get_prompt_number(self, cell):
+        return cell.prompt_number if hasattr(cell, 'prompt_number') \
+            else self.blank_symbol
+
     def dispatch(self, cell_type):
         """return cell_type dependent render method,  for example render_code
         """

converters/html.py

@@ -11,6 +11,7 b' import io'
 
 class ConverterHTML(Converter):
     extension = 'html'
+    blank_symbol = ' '
 
     def in_tag(self, tag, src, attrs=None):
         """Return a list of elements bracketed by the given tag"""
@@ -29,8 +30,7 b' class ConverterHTML(Converter):'
 
     def _out_prompt(self, output):
         if output.output_type == 'pyout':
-            n = output.prompt_number if output.prompt_number is not None else ' '
-            content = 'Out[%s]:' % n
+            content = 'Out[%s]:' % self._get_prompt_number(output)
         else:
             content = ''
         return ['<div class="prompt output_prompt">%s</div>' % content]
@@ -93,7 +93,7 b' class ConverterHTML(Converter):'
         lines = ['<div class="cell border-box-sizing code_cell vbox">']
         
         lines.append('<div class="input hbox">')
-        n = cell.prompt_number if getattr(cell, 'prompt_number', None) is not None else '&nbsp;'
+        n = self._get_prompt_number(cell)
         lines.append('<div class="prompt input_prompt">In&nbsp;[%s]:</div>' % n)
         lines.append('<div class="input_area box-flex1">')
         lines.append(highlight(cell.input))

converters/markdown.py

@@ -19,10 +19,11 b' class ConverterMarkdown(Converter):'
         if not cell.input:
             return []
         lines = []
+        n = self._get_prompt_number(cell)
         if self.show_prompts and not self.inline_prompt:
-            lines.extend(['*In[%s]:*' % cell.prompt_number, ''])
+            lines.extend(['*In[%s]:*' % n, ''])
         if self.show_prompts and self.inline_prompt:
-            prompt = 'In[%s]: ' % cell.prompt_number
+            prompt = 'In[%s]: ' % n
             input_lines = cell.input.split('\n')
             src = prompt + input_lines[0] + '\n' + indent('\n'.join(input_lines[1:]), nspaces=len(prompt))
         else:
@@ -30,7 +31,7 b' class ConverterMarkdown(Converter):'
         src = highlight(src) if self.highlight_source else indent(src)
         lines.extend([src, ''])
         if cell.outputs and self.show_prompts and not self.inline_prompt:
-            lines.extend(['*Out[%s]:*' % cell.prompt_number, ''])
+            lines.extend(['*Out[%s]:*' % n, ''])
         for output in cell.outputs:
             conv_fn = self.dispatch(output.output_type)
             lines.extend(conv_fn(output))
@@ -52,7 +53,7 b' class ConverterMarkdown(Converter):'
         lines = []
         
         ## if 'text' in output:
-        ##     lines.extend(['*Out[%s]:*' % output.prompt_number, ''])
+        ##     lines.extend(['*Out[%s]:*' % self._get_prompt_number(cell), ''])
 
         # output is a dictionary like object with type as a key
         if 'latex' in output:

converters/python.py

@@ -33,21 +33,17 b' class ConverterPy(Converter):'
         return ['#{0} {1}'.format('#'*cell.level, cell.source), '']
 
     def render_code(self, cell):
-        try:
-            prompt_number = cell.prompt_number
-        except AttributeError:
-            prompt_number = " "
-
+        n = self._get_prompt_number(cell)
         if not cell.input:
             return []
         lines = []
         if self.show_prompts:
-            lines.extend(['# In[%s]:' % prompt_number])
+            lines.extend(['# In[%s]:' % n])
         src = cell.input
         lines.extend([src, ''])
         if self.show_output:
             if cell.outputs :
-                lines.extend(['# Out[%s]:' % prompt_number])
+                lines.extend(['# Out[%s]:' % n])
             for output in cell.outputs:
                 conv_fn = self.dispatch(output.output_type)
                 lines.extend(conv_fn(output))
@@ -66,7 +62,7 b' class ConverterPy(Converter):'
         lines = []
 
         ## if 'text' in output:
-        ##     lines.extend(['*Out[%s]:*' % output.prompt_number, ''])
+        ##     lines.extend(['*Out[%s]:*' % self._get_prompt_number(cell), ''])
 
         # output is a dictionary like object with type as a key
         if 'latex' in output:

converters/rst.py

@@ -15,12 +15,7 b' class ConverterRST(Converter):'
         if not cell.input:
             return []
 
-        try:
-            prompt_number = cell.prompt_number
-        except AttributeError:
-            prompt_number = " "
-
-        lines = ['In[%s]:' % prompt_number, '']
+        lines = ['In[%s]:' % self._get_prompt_number(cell), '']
         lines.extend(rst_directive('.. code:: python', cell.input))
 
         for output in cell.outputs:
@@ -40,7 +35,7 b' class ConverterRST(Converter):'
             return [cell.source]
 
     def render_pyout(self, output):
-        lines = ['Out[%s]:' % output.prompt_number, '']
+        lines = ['Out[%s]:' % self._get_prompt_number(output), '']
 
         # output is a dictionary like object with type as a key
         if 'latex' in output: