254   \end{lstlisting}

   254   \end{lstlisting}

   255 \alert{Now run python four\_plot.py again}

   255 \alert{Now run python four\_plot.py again}

   256 \end{frame}

   256 \end{frame}

   257 

   257 

   258 \begin{frame}[fragile]

   258 \begin{frame}[fragile]

   259   \begin{lstlisting}

   260   \begin{lstlisting}

   260 Traceback (most recent call last):

   261 Traceback (most recent call last):

   261   File "four_plot.py", line 1, in <module>

   262   File "four_plot.py", line 1, in <module>

   262     x = plot(x, x, 'b')

   263     x = plot(x, x, 'b')

   263 NameError: name 'plot' is not defined

   264 NameError: name 'plot' is not defined