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