code: def post(self, relpath=None, params=None, data=None, contenttype=None):
      
      return self.invoke("POST", relpath, params, data,
                         self._make_headers(contenttype))
docs: Invoke the POST method on a resource.
      @param relpath: Optional. A relative path to this resource's path.
      @param params: Key-value data.
      @param data: Optional. Body of the request.
      @param contenttype: Optional.
  
      @return: A dictionary of the JSON result.