code: def get_vertex_schema_element_or_raise(self, vertex_classname):
          
          schema_element = self.get_element_by_class_name_or_raise(vertex_classname)
  
          if not schema_element.is_vertex:
              raise InvalidClassError(u'Non-vertex class provided: {}'.format(vertex_classname))
  
          return schema_element
docs: Return the schema element with the given name, asserting that it's of vertex type.