code: def head(self, n=None, **kwargs):
          
          if n is None:
              n = options.display.max_rows
          return self._handle_delay_call('execute', self, head=n, **kwargs)
docs: Return the first n rows. Execute at once.
  
          :param n:
          :return: result frame
          :rtype: :class:`odps.df.backends.frame.ResultFrame`