python實例屬性管理

在python中，需要對某個實例attribute增加除訪問與修改之外的其他處理邏輯，比如類型檢查或合法性驗證。下面通過兩種方法進行實現。(具體參考《python cookbook》)

# -*- coding:utf-8 -*-

#getter和setter主要用於實例屬性的檢測

#以下是通過類的方式實現的實例屬性的檢測，
#但是如果有很多屬性需要檢測，則將實現很多冗餘的代碼。
#因此可以通過第二種方法進行解決。
class NameAge:
    def __init__(self, name, age):
        self._name = name
        self._age = age

    @property
    def name(self):
        return self._name

    @name.setter
    def name(self, value):
        if not isinstance(value, str):
            raise TypeError("name must be a string")
        else:
            self._name = value

    @property
    def age(self):
        return self._age

    @age.setter
    def age(self, value):
        if not isinstance(value, int):
            raise TypeError("age must be a int")
        else:
            self._age = value


#第二種方法
def typed_property(name, expected_type):
    storage_name = '%s%s' %('_', name)

    @property
    def proper(self):
        return getattr(self, storage_name)

    @proper.setter
    def proper(self, value):
        if not isinstance(value, expected_type):
            raise TypeError("{0} must be a {1}".format(name, expected_type))
        else:
            setattr(self, storage_name, value)

    return proper

class NameAge2:
    name = typed_property('name', str)
    age = typed_property('age', int)

    def __init__(self, name, age):
        self.name = name
        self.age = age


def main():
    obj1 = NameAge("alice", 10)
    print("Obj1 -> name: {0} age: {1}".format(obj1.name, obj1.age))
    obj1.name = "david"
    obj1.age = 20
    print("Obj1 -> name: {0} age: {1}".format(obj1.name, obj1.age))
    #異常
    #obj1.name = 10

    obj2 = NameAge2("alex", 11)
    print("Obj2 -> name: {0} age: {1}".format(obj2.name, obj2.age))
    obj2.name = "bob"
    obj2.age = 13
    print("Obj2 -> name: {0} age: {1}".format(obj2.name, obj2.age))
    #異常
    #obj2.age = 'tila'

if __name__ == "__main__":
    main()

運行結果：

Obj1 -> name: alice age: 10
Obj1 -> name: david age: 20
Obj2 -> name: alex age: 11
Obj2 -> name: bob age: 13