code: def to_notebook(self, s, **kwargs):
          
          all_blocks = self.parse_blocks(s)
          if self.pre_code_block['content']:
              # TODO: if first block is markdown, place after?
              all_blocks.insert(0, self.pre_code_block)
  
          blocks = [self.process_code_block(block) for block in all_blocks]
  
          cells = self.create_cells(blocks)
  
          nb = nbbase.new_notebook(cells=cells)
  
          return nb
docs: Convert the markdown string s to an IPython notebook.
  
          Returns a notebook.