code: def _add_documentation_link(self, links, section, variable_name, default=None):
          
  
          url = getattr(sys.modules['__main__'], variable_name, default)
  
          if url:
              links.append('%s: %s' % (section, url))
docs: :param list links: List of links to append link of the form "Section: <link>", if link available
            :param str section: Name of the section (concept, command line options, API reference)
            :param str variable_name: Variable name in main module that should hold URL to documentation
            :param str default: Default URL to documentation