code: def add_error(self, error):
          
          self._count += 1
          self._record.add_error('expect@%s+%s' % (time.time(), self._count),
                                 error)
docs: Record an error from expect APIs.
  
          This method generates a position stamp for the expect. The stamp is
          composed of a timestamp and the number of errors recorded so far.
  
          Args:
              error: Exception or signals.ExceptionRecord, the error to add.