code: def addBoth(self, callback, *args, **kw):
          
          return self.addCallbacks(callback, callback, args, kw, args, kw)
docs: Add a single callback as both success and failure callbacks.
  
          @return: C{self}
          @rtype: L{DeferredContext}
  
          @raises AlreadyFinished: L{DeferredContext.addActionFinish} has been
              called. This indicates a programmer error.