php Python描述符

class Descriptor:
    def __init__(self, name, type, default=None):
        self.name = "_" + name
        self.type = type
        self.default = default if default else type()

    def __get__(self, instance, cls):
        return getattr(instance, self.name, self.default)

    def __set__(self, instance, value):
        if not isinstance(value, self.type):
            raise TypeError("Must be a %s" % self.type)
        setattr(instance, self.name, value)

    def __delete__(self, instance):
        raise AttributeError("Can't delete attribute")

class Foo:
    name = Descriptor("name", str)
    num  = Descriptor("num", int, 42)

f = Foo()
a = f.name
f.name = "Guido"
del f.name   # Raise AttributeError
//该片段来自于http://outofmemory.cn