code: def cbar_value_cb(self, cbar, value, event):
          
          if self.cursor_obj is not None:
              readout = self.cursor_obj.readout
              if readout is not None:
                  maxv = readout.maxv
                  text = "Value: %-*.*s" % (maxv, maxv, value)
                  readout.set_text(text)
docs: This method is called when the user moves the mouse over the
          ColorBar.  It displays the value of the mouse position in the
          ColorBar in the Readout (if any).