code: def plot_clicked(self, mouse_event):
          
          if type(self.peak_vals) is list:
              self.peak_vals.append([mouse_event.xdata, mouse_event.ydata])
              axes = self.matplotlibwidget.axes
              # can't use patches, as they use data coordinates for radius but this is a high aspect ratio plot so the
              # circle was extremely stretched
              axes.plot(mouse_event.xdata, mouse_event.ydata, 'ro', markersize = 5)
  
              # axes.text(mouse_event.xdata, mouse_event.ydata, '{:d}'.format(len(self.peak_vals[-1])),
              #                  horizontalalignment='center',
              #                  verticalalignment='center',
              #                  color='black'
              #                  )
              self.matplotlibwidget.draw()
docs: When a click is registered on the plot, appends the click location to self.peak_vals and plots a red dot in the
          click location
          :param mouse_event: a mouse event object for the click