code: def get_template_vars(self, slides):
          
          try:
              head_title = slides[0]['title']
          except (IndexError, TypeError):
              head_title = "Untitled Presentation"
  
          for slide_index, slide_vars in enumerate(slides):
              if not slide_vars:
                  continue
              self.num_slides += 1
              slide_number = slide_vars['number'] = self.num_slides
              if slide_vars['level'] and slide_vars['level'] <= TOC_MAX_LEVEL:
                  self.add_toc_entry(slide_vars['title'], slide_vars['level'],
                                     slide_number)
              else:
                  # Put something in the TOC even if it doesn't have a title or level
                  self.add_toc_entry(u"-", 1, slide_number)
  
          return {'head_title': head_title, 'num_slides': str(self.num_slides),
                  'slides': slides, 'toc': self.toc, 'embed': self.embed,
                  'css': self.get_css(), 'js': self.get_js(),
                  'user_css': self.user_css, 'user_js': self.user_js,
                  'math_output': self.math_output}
docs: Computes template vars from slides html source code.