docstr: Measures whether result is ready and loaded w/o printing
docstr_tok: ["Measures","whether","result","is","ready","and","loaded","w\/o","printing"]
code: def successful(self):
      "Measures whether result is ready and loaded w/o printing"
      assert self.ready()
      if not self.unpickled:
          self.__unpickle()
      return self._success
  
imports: from ppft import _Task
  from ppft import Server
  import time
  import dill
  import threading
label_desc: Use image node_id 9 for calling the MapResult obj's underlying member method code with example usage: obj.successful() and returns: self