code: def _load_symbol(name):
      
      module_name, key = name.rsplit('.', 1)
      try:
          module = importlib.import_module(module_name)
      except ImportError as err:
          # it's possible the symbol is a class method
          module_name, class_name = module_name.rsplit('.', 1)
          module = importlib.import_module(module_name)
          cls = getattr(module, class_name, None)
          if cls:
              attr = getattr(cls, key, None)
          else:
              raise err
      else:
          attr = getattr(module, key, None)
      if not callable(attr):
          raise ValueError('%s is not callable (was %r)' % (name, attr))
      return attr
docs: Load a symbol by name.
  
      :param str name: The name to load, specified by `module.attr`.
      :returns: The attribute value. If the specified module does not contain
                the requested attribute then `None` is returned.