ポリシーパターン

Appendix-1 クラスを用いた実装例

import abc

class Rule(metaclass=abc.ABCMeta):
    @abc.abstractmethod
    def is_ok(self, value):
        pass

class Rule001(Rule):
    def is_ok(self, value):
        return (value.type == 'special')

class Rule002(Rule):
    def is_ok(self, value):
        return (value.price == 0)

class Rule003(Rule):
    def is_ok(self, value):
        return (value.unit >= 10)

class Policy:
    def __init__(self):
        self.rules = []

    def add(self, rule):
        self.rules.append(rule)

    def is_comply(self, value):
        for rule in self.rules:
            if not rule.is_ok(value):
                return False
        return True

if __name__=='__main__':
    # 正常データ
    value1 = {
        type: "special",
        price: 0,
        unit: 10
    }
    p = Policy()
    p.add(Rule001())
    p.add(Rule002())
    p.add(Rule003())
    result = p.is_comply(value1)
    print(result)   # => True

    # 異常データ
    value2 = {
        type: "standard",
        price: 1000,
        unit: 5
    }
    p = Policy()
    p.add(Rule001())
    p.add(Rule002())
    p.add(Rule003())
    result = p.is_comply(value2)
    print(result)   # => Flase

Appendix-2 関数を用いた実装例

def rule_001(value):
    return (value.type == 'special')

def rule_002(value):
    return (value.price == 0)

def rule_003(value):
    return (value.unit >= 10)

def check_policy(value):
    rules = [rule_001, rule_002, rule_003]
    for rule in rules:
        if not rule(value):
            return Flase
    return True


if __name__=='__main__':
    # 正常データ
    value1 = {
        type: "special",
        price: 0,
        unit: 10
    }
    result = check_policy(value1)
    print(result)   # => True

    # 異常データ
    value2 = {
        type: "standard",
        price: 1000,
        unit: 5
    }
    result = check_policy(value2)
    print(result)   # => Flase