code: def plot_returns(returns,
                   live_start_date=None,
                   ax=None):
      
  
      if ax is None:
          ax = plt.gca()
  
      ax.set_label('')
      ax.set_ylabel('Returns')
  
      if live_start_date is not None:
          live_start_date = ep.utils.get_utc_timestamp(live_start_date)
          is_returns = returns.loc[returns.index < live_start_date]
          oos_returns = returns.loc[returns.index >= live_start_date]
          is_returns.plot(ax=ax, color='g')
          oos_returns.plot(ax=ax, color='r')
  
      else:
          returns.plot(ax=ax, color='g')
  
      return ax
docs: Plots raw returns over time.
  
      Backtest returns are in green, and out-of-sample (live trading)
      returns are in red.
  
      Parameters
      ----------
      returns : pd.Series
          Daily returns of the strategy, noncumulative.
           - See full explanation in tears.create_full_tear_sheet.
      live_start_date : datetime, optional
          The date when the strategy began live trading, after
          its backtest period. This date should be normalized.
      ax : matplotlib.Axes, optional
          Axes upon which to plot.
      **kwargs, optional
          Passed to plotting function.
  
      Returns
      -------
      ax : matplotlib.Axes
          The axes that were plotted on.