Python Block Callback Usage

In an attempt to understand the mechanism of resetting a Head block I developed the attached flowgraph as a test. I want to be able to reset the Head block using the Check Box.

 

The comments in the Python Block state:

# if an attribute with the same name as a parameter is found,          # a callback is registered

I don't understand what the callback method is called. I have tried using Reset and _Reset_callback but the callback is never called.

Also, you might comment on my attempt to call reset() in the Head block – is this correct? 

Jim

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