The meaning of ax.plot( Xs, [0] * FLAGS.data_length, 'b', lw=3, alpha=0.5, label='steering')

The meaning of this line of code is to use the ax.plot function in the matplotlib library to draw a line chart with the specified number (FLAGS.data_length) in the Xs variable, and add the b variable to the line, set the line width to 3, and the transparency to 0.5. And use steering as the legend label.