linewidth

can someone tell me why the lines on the plot are drawn with a linewidth of 1 instead of 5?

     def init_plot_data(self):
         self.axes = self.fig.add_subplot(111)
         self.xrange = numpy.arange(80)
         self.yrange = range(80)
         random.shuffle(self.yrange)
         yrange = numpy.array(self.yrange)
         self.axes.plot(self.xrange, self.yrange, lw=5)

thanks,

bryan