code: def get_sphinx_ref(self, url, label=None):
          
  
          # Raise an exception if the initial part of url does not match
          # the base url for this object
          n = len(self.baseurl)
          if url[0:n] != self.baseurl:
              raise KeyError('base of url %s does not match base url %s' %
                             (url, self.baseurl))
          # The reverse lookup key is either the full url or the postfix
          # to the base url, depending on flag addbase
          if self.addbase:
              pstfx = url[n:]
          else:
              pstfx = url
  
          # Look up the cross-reference role and referenced object
          # name via the postfix to the base url
          role, name = self.revinv[pstfx]
  
          # If the label string is provided and is shorter than the name
          # string we have lookup up, assume it is a partial name for
          # the same object: append a '.' at the front and use it as the
          # object name in the cross-reference
          if label is not None and len(label) < len(name):
              name = '.' + label
  
          # Construct cross-reference
          ref = ':%s:`%s`' % (role, name)
          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).