code: def __subscribeImpl(self, handler):
      assert not self.__emitting
      if handler not in self.__handlers:
          self.__handlers.append(handler)
  
imports: import abc
  import six
  from pyalgotrade import dispatchprio
label_desc: Use image node_id 2 for calling the Event obj's underlying member method code with example usage: obj.__subscribeImpl(handler) without return types