select point in a graph using keyboard,not clicj event

[ferri_marllo gva es]

Hello!!
I,ve built an appilcation which plot a graph into a canvas,i'd like to connect
two signals to it...one of this is to move a cursor inside(key_press_event),but
i'd like too that eaxh time i press c in a graph(on point)it will be seected...
how can i do it