def METHOD_NAME(self, event):
    if self.range is None:
        # The ColorMapper doesn't have a range yet, so don't do anything.
        # This apparently occurs during initialization.
        return
    if self.data_func is not None:
        low = self.range.low
        high = self.range.high
        trans_low = self.data_func(low)
        trans_high = self.data_func(high)
        self.transformed_bounds = (trans_low, trans_high)
    else:
        self.transformed_bounds = (None, None)
    self.updated = True