code: def url(self):
          
          if not 'self' in self.links:
              return None
  
          self_link = self.links['self']
  
          if isinstance(self_link, list):
              for link in self_link:
                  return link.url()
  
          return self_link.url()
docs: Returns the URL for the resource based on the ``self`` link.
  
          This method returns the ``href`` of the document's ``self`` link if it
          has one, or ``None`` if the document lacks a ``self`` link, or the
          ``href`` of the document's first ``self`` link if it has more than one.