def METHOD_NAME(event):
    item = event.item
    if item == "item_1_value":
        source.data = dict(x=[10, 20], y=[10, 10])
    elif item == "item_2_value":
        source.data = dict(x=[100, 200], y=[100, 100])
    elif item == "item_3_value":
        source.data = dict(x=[1000, 2000], y=[1000, 1000])