动态更新Python属性设置方法

Question

我想给一个值动态添加一个“可锁定”的功能。虽然这个例子看起来很简单，甚至有点牵强，但我想把我的可锁定混合类扩展到不同的使用场景。我不想只做一个一次性的可锁定值，而是希望它足够通用，可以控制多个类的属性。

我希望在完成后，最后的检查能通过。

我尝试用super代替self.setattr，但遇到了一个错误，提示这个属性是只读的。这让我开始怀疑我是否能实现我想要的功能。

任何帮助都非常感谢，提前谢谢大家！

一些代码：

from collections import OrderedDict as OD


def lockable(func, locked=None):
    def wrapper(*args, **kwds):
        if locked:
            val = None
        else:
            val = func(*args, **kwds)
        return val
    return wrapper


class Mixin(object):

    @property
    def meta(self):
        attr = "__meta__"
        if not hasattr(self, attr):
            setattr(self, attr, OD())
        return getattr(self, attr)


class LockableMixin(Mixin):

    @property
    def locked(self):
        self.meta.setdefault("locked", False)
        return self.meta.get("locked")

    @locked.setter
    def locked(self, value):
        value = value if value in [None, True, False] else self.meta['locked']
        self.meta['locked'] = value

    def lock(self):
        self.locked = True

    def unlock(self):
        self.locked = False

    def is_locked(self):
        return self.locked

    def __init__(self):
        super(LockableMixin, self).__init__()
        self.__setattr__ = lockable(self.__setattr__, self.locked)


class Attribute(object):

    @property
    def value(self):
        attr = "__value__"
        if not hasattr(self, attr):
            setattr(self, attr, False)
        return getattr(self, attr)

    @value.setter
    def value(self, value):
        self.__value__ = value

    def __init__(self, value):
        self.value = value
        super(Attribute, self).__init__()

    def __get__(self, instance, owner):
        return self.value

    def __set__(self, instance, value):
        self.value = value

    def __str__(self):
        return str(self.value)

    def __repr__(self):
        cname = self.__class__.__name__
        value = str(self.value)
        return "<%s %s>" % (cname, value)


class LockableAttribute(Attribute, LockableMixin):
    pass

if __name__ == "__main__":
    a1 = Attribute(1)
    a2 = LockableAttribute(1)
    assert a2.locked is False
    assert a2.value == 1
    a2.lock()
    assert a2.locked is True
    a2.unlock()
    assert a2.locked is False
    a2.value = 2
    assert a2.value == 2
    a2.locked = True
    a2.value = 3
    assert a2.value == 2    # This will raise an exception, but it shouldn't.

这里有一个组件类的使用案例：

class Component(object):

    @property
    def attributes(self):
        attrs = {}
        for field in self.__fields__:
            attrs[field] = self.get(field)
        return attrs

    def __init__(self, **attributes):
        super(Component, self).__init__()
        self.__fields__ = []
        for name, val in attributes.iteritems():
            if name not in self.__fields__:
                self.__fields__.append(name)
                setattr(self, name, val)

    def __setattr__(self, name, value):
        if not name.startswith("__"):
            if not isinstance(value, Attribute):
                value = Attribute(value)
        super(Component, self).__setattr__(name, value)

    def __getitem__(self, name):
        return getattr(self, name, None)

    def get(self, name, default=None):
        return getattr(self, name, default)

# Case 1:  a lockable attribute
c = Component(name="Joe Schmoe", dob=LockableDateAttribute("04/12/2014"))

c.dob.lock()
c.dob.unlock()

# Case 2:  a lockable component class containing arbitrary number of lockable attributes
c2 = LockableComponent(name="Jill Pill", dob=LockableDateAttribute("04/12/2014))
c2.lock()   #  locks all of the lockable attributes

动态更新代码示例只读属性 super函数混合类动态属性属性控制可锁定功能

动态更新Python属性设置方法

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