python3（二十七）property

"""  """
__author__ = 'shaozhiqi'


# 绑定属性时，如果我们直接把属性暴露出去，虽然写起来很简单，
# 但是，没办法检查参数，导致可以把参数随便改
# 比如想限制student score的范围

class Student(object):

    def get_score(self):
        return self._score

    def set_score(self, value):
        if not isinstance(value, int):
            raise ValueError('score must be an integer!')
        if value < 0 or value > 100:
            raise ValueError('score must between 0 ~ 100!')
        self._score = value


s = Student()
s.set_score(60)
print(s.get_score())  # 60


# print(s.set_score(1000))  # ValueError: score must between 0 ~ 100!


# ---------------------property-------------------------------------
# 上述方法不太简洁,使用property 修改
# @property装饰器就是负责把一个方法变成属性调用,默认是只读
class Student1(object):

    @property
    def score(self):
        return self._score

    @score.setter
    def score(self, value):
        if not isinstance(value, int):
            raise ValueError('score must be an integer!')
        if value < 0 or value > 100:
            raise ValueError('score must between 0 ~ 100!')
        self._score = value


s1 = Student1()
s1.score = 60


# s1.score = 9999999  # ValueError: score must between 0 ~ 100!


# 报错说明里面有set 方法的实现，如果直接暴露的属性，就不会报错

# 只读属性-------------------------------------------------------
class Student(object):

    @property
    def birth(self):
        return self._birth

    @birth.setter
    def birth(self, value):
        self._birth = value

    @property
    def age(self):
        return 2019 - self._birth


# birth 是一个可读写属性，而age是一个只读属性
#  age的值可以根据birth计算

s = Student()
s.birth = 1990
print(s.birth)  # 注意如果不赋值直接读 会error
# s.age=100  # error AttributeError: can't set attribute  property 默认是只读
print(s.age)  # 29