old_contents: # encoding: UTF-8
  from Queue import Queue
  
  from enum import Enum
  
  
  class PromiseResultType(Enum):
      Result = 1
      Exception = 2
  
  
  class Promise(object):
      """
      用队列实现的一个简单的Promise类型
      """
      
      def __init__(self):
          self._queue = Queue()
      
      def set_result(self, val):
          self._queue.put((PromiseResultType.Result, val))
      
      def get(self, timeout=None):
          res = self._queue.get(timeout=timeout)
          if res[0] == PromiseResultType.Result:
              return res[1]
          raise res[2]
      
      def set_exception(self, val):
          self._queue.put((PromiseResultType.Exception, val))
  
new_contents: # encoding: UTF-8
  from Queue import Queue
  
  from enum import Enum
  
  
  class PromiseResultType(Enum):
      Result = 1
      Exception = 2
  
  
  class Promise(object):
      """
      用队列实现的一个简单的Promise类型
      """
      
      def __init__(self):
          self._queue = Queue()
      
      def set_result(self, val):
          self._queue.put((PromiseResultType.Result, val))
      
      def get(self, timeout=None):
          res = self._queue.get(timeout=timeout)
          if res[0] == PromiseResultType.Result:
              return res[1]
          raise res[1]
      
      def set_exception(self, val):
          self._queue.put((PromiseResultType.Exception, val))
  
subject: 修正一个Bug：调用tests.Promise.set_exception后无法正常抛出异常