code: def create_failure(self, exception=None):
          
          if exception:
              return FailedFuture(type(exception), exception, None)
          return FailedFuture(*sys.exc_info())
docs: This returns an object implementing IFailedFuture.
  
          If exception is None (the default) we MUST be called within an
          "except" block (such that sys.exc_info() returns useful
          information).