code: def get_sphinx_ref(self, url, label=None):
          
  
          # A url is assumed to correspond to a citation if it contains
          # 'zreferences.html#'
          if 'zreferences.html#' in url:
              key = url.partition('zreferences.html#')[2]
              ref = ':cite:`%s`' % key
          else:
              # If the url does not correspond to a citation, try to look it
              # up in each of the IntersphinxInventory objects in our list
              ref = None
              # Iterate over IntersphinxInventory objects in our list
              for ii in self.invlst:
                  # If the baseurl for the current IntersphinxInventory
                  # object matches the url, try to look up the reference
                  # from the url and terminate the loop of the look up
                  # succeeds
                  if ii.matching_base_url(url):
                      ref = ii.get_sphinx_ref(url, label)
                      break
  
              if ref is None:
                  raise KeyError('no match found for url %s' % url)
  
          return ref
docs: Get an internal sphinx cross reference corresponding to `url`
          into the online docs, associated with a link with label `label`
          (if not None).