code: def addCallbacks(
          self,
          callback,
          errback=None,
          callbackArgs=None,
          callbackKeywords=None,
          errbackArgs=None,
          errbackKeywords=None
      ):
          
          if self._finishAdded:
              raise AlreadyFinished()
  
          if errback is None:
              errback = _passthrough
  
          def callbackWithContext(*args, **kwargs):
              return self._action.run(callback, *args, **kwargs)
  
          def errbackWithContext(*args, **kwargs):
              return self._action.run(errback, *args, **kwargs)
  
          self.result.addCallbacks(
              callbackWithContext, errbackWithContext, callbackArgs,
              callbackKeywords, errbackArgs, errbackKeywords)
          return self
docs: Add a pair of callbacks that will be run in the context of an eliot
          action.
  
          @return: C{self}
          @rtype: L{DeferredContext}
  
          @raises AlreadyFinished: L{DeferredContext.addActionFinish} has been
              called. This indicates a programmer error.