class GUIThing(HasTraits):
    my_slider_low = 0.0
my_slider_hi = 1.0
my_slider = Range(low='my_slider_low', high='my_slider_hi', value=0.1)

def __init__(self, arg1):
    self.my_slider_hi = arg1
view = View(Item('my_slider'))
top_range = 0.2
my_gui = GUIThing(top_range)
my_gui.configure_traits()
Change property parameter from within class constructor [Python / Traits]