def get_value_for_expr(self, expr, target):
        if expr in LOGICAL_OPERATORS.values():
            return None
        rvalue = expr['value']
        if rvalue == HISTORICAL:
            history = self.history[target]
            if len(history) < self.history_size:
                return None
            rvalue = sum(history) / float(len(history))

        rvalue = expr['mod'](rvalue)
        return rvalue
Decorate a function as an IRC command, with custom names
dataset/ETHPy150Open klen/graphite-beacon/graphite_beacon/alerts.py/BaseAlert.get_value_for_expr--crossover with--dataset/ETHPy150Open sbp/duxlot/functions.py/named