[Discuss-gnuradio] GRC QT widget call function upon value change?

Is there a way to make a GRC widget, such as the QT GUI Chooser, call a function when it changes value?

I have some serial port writing functions defined in a Python Module block.  I set the GUI Chooser options to write_serial(0), write_serial(1), etc..  The problem is the functions are evaluated only once during top_block execution, not when the Chooser value is changed.

I have tried a Function Probe to pass the Chooser value to my write_serial() once a second, but the Function Probe does not update with the new Chooser value.

Is there some trick to this?

Thanks,

Lou