code: def last(series, order_by=None):
      
  
      if order_by is not None:
          series = order_series_by(series, order_by)
      last_s = series.iloc[series.size - 1]
      return last_s
docs: Returns the last value of a series.
  
      Args:
          series (pandas.Series): column to summarize.
  
      Kwargs:
          order_by: a pandas.Series or list of series (can be symbolic) to order
              the input series by before summarization.