规约模式和状态模式 17/30 | Python 主题月

写在前面

本文正在参加「Python主题月」，详情查看活动链接

这个月是 Python 活动月，我决定尝试用 Python 来刷这 30 天的每日一题和随机一题。然后如果周末有精力，我想捣鼓捣鼓这个python-patterns

设计模式对我来说更多的是学习而不是我的个人经验总结，所以我很可能理解偏，如果有大佬见到了请及时指出，我之所以选择在掘金来写一些个人的东西是因为这里的文章质量更高，我不希望后来者看到了这些文章被误导。

规约模式

from abc import abstractmethod


class Specification:
    def and_specification(self, candidate):
        raise NotImplementedError()

    def or_specification(self, candidate):
        raise NotImplementedError()

    def not_specification(self):
        raise NotImplementedError()

    @abstractmethod
    def is_satisfied_by(self, candidate):
        pass


class CompositeSpecification(Specification):
    @abstractmethod
    def is_satisfied_by(self, candidate):
        pass

    def and_specification(self, candidate):
        return AndSpecification(self, candidate)

    def or_specification(self, candidate):
        return OrSpecification(self, candidate)

    def not_specification(self):
        return NotSpecification(self)


class AndSpecification(CompositeSpecification):
    _one = Specification()
    _other = Specification()

    def __init__(self, one, other):
        self._one = one
        self._other = other

    def is_satisfied_by(self, candidate):
        return bool(
            self._one.is_satisfied_by(candidate)
            and self._other.is_satisfied_by(candidate)
        )


class OrSpecification(CompositeSpecification):
    _one = Specification()
    _other = Specification()

    def __init__(self, one, other):
        self._one = one
        self._other = other

    def is_satisfied_by(self, candidate):
        return bool(
            self._one.is_satisfied_by(candidate)
            or self._other.is_satisfied_by(candidate)
        )


class NotSpecification(CompositeSpecification):
    _wrapped = Specification()

    def __init__(self, wrapped):
        self._wrapped = wrapped

    def is_satisfied_by(self, candidate):
        return bool(not self._wrapped.is_satisfied_by(candidate))


class User:
    def __init__(self, super_user=False):
        self.super_user = super_user


class UserSpecification(CompositeSpecification):
    def is_satisfied_by(self, candidate):
        return isinstance(candidate, User)


class SuperUserSpecification(CompositeSpecification):
    def is_satisfied_by(self, candidate):
        return getattr(candidate, "super_user", False)


def main():
    """
    >>> andrey = User()
    >>> ivan = User(super_user=True)
    >>> vasiliy = 'not User instance'

    >>> root_specification = UserSpecification().and_specification(SuperUserSpecification())

    # Is specification satisfied by <name>
    >>> root_specification.is_satisfied_by(andrey), 'andrey'
    (False, 'andrey')
    >>> root_specification.is_satisfied_by(ivan), 'ivan'
    (True, 'ivan')
    >>> root_specification.is_satisfied_by(vasiliy), 'vasiliy'
    (False, 'vasiliy')
    """


if __name__ == "__main__":
    import doctest

    doctest.testmod()

状态模式

class State:

    """Base state. This is to share functionality"""

    def scan(self):
        """Scan the dial to the next station"""
        self.pos += 1
        if self.pos == len(self.stations):
            self.pos = 0
        print("Scanning... Station is {} {}".format(self.stations[self.pos], self.name))


class AmState(State):
    def __init__(self, radio):
        self.radio = radio
        self.stations = ["1250", "1380", "1510"]
        self.pos = 0
        self.name = "AM"

    def toggle_amfm(self):
        print("Switching to FM")
        self.radio.state = self.radio.fmstate


class FmState(State):
    def __init__(self, radio):
        self.radio = radio
        self.stations = ["81.3", "89.1", "103.9"]
        self.pos = 0
        self.name = "FM"

    def toggle_amfm(self):
        print("Switching to AM")
        self.radio.state = self.radio.amstate


class Radio:

    """A radio.     It has a scan button, and an AM/FM toggle switch."""

    def __init__(self):
        """We have an AM state and an FM state"""
        self.amstate = AmState(self)
        self.fmstate = FmState(self)
        self.state = self.amstate

    def toggle_amfm(self):
        self.state.toggle_amfm()

    def scan(self):
        self.state.scan()


def main():
    """
    >>> radio = Radio()
    >>> actions = [radio.scan] * 2 + [radio.toggle_amfm] + [radio.scan] * 2
    >>> actions *= 2

    >>> for action in actions:
    ...    action()
    Scanning... Station is 1380 AM
    Scanning... Station is 1510 AM
    Switching to FM
    Scanning... Station is 89.1 FM
    Scanning... Station is 103.9 FM
    Scanning... Station is 81.3 FM
    Scanning... Station is 89.1 FM
    Switching to AM
    Scanning... Station is 1250 AM
    Scanning... Station is 1380 AM
    """


if __name__ == "__main__":
    import doctest

    doctest.testmod()

小结

参考文献

• 无