code: def get_instance(page_to_crawl):
      
      global _instances
      if isinstance(page_to_crawl, basestring):
          uri = page_to_crawl
          page_to_crawl = crawlpage.get_instance(uri)
      elif isinstance(page_to_crawl, crawlpage.CrawlPage):
          uri = page_to_crawl.uri
      else:
          raise TypeError(
              "get_instance() expects a parker.CrawlPage "
              "or basestring derivative."
          )
  
      try:
          instance = _instances[uri]
      except KeyError:
          instance = CrawlModel(page_to_crawl)
          _instances[uri] = instance
  
      return instance
docs: Return an instance of CrawlModel.