':param variable: The variable whose transformed value is returned.
:type variable: int or str or :obj:`~Orange.data.DiscreteVariable`
:param lookup_table: transformations for each value of `self.variable`
:type lookup_table: np.array or list or tuple
:param unknown: The value to be used as unknown value.
:type unknown: float or int'

def __init__(self, variable, lookup_table, unknown=np.nan):

    super().__init__(variable)
    self.lookup_table = lookup_table
    self.unknown = unknown
