猴子補丁、屬性裝飾器

Monkey Patch

在運行時，對屬性進行動態替換（黑魔法，慎用）

# test1.py


class Person:
    def __init__(self, chi, eng, his):
        self.chi = chi
        self.eng = eng
        self.his = his

    def get_score(self):
        return self.chi, self.eng, self.his


# test2.py


def get_score(self):
    return dict(chi=self.chi, eng=self.eng, his=self.his)



# test3.py
from test2 import get_score
from test1 import Person


def monkeypatch4Person():
    Person.get_score = get_score


stu1 = Person(60, 70, 80)
print(stu1.get_score())

monkeypatch4Person()
print(stu1.get_score())



out:
(60, 70, 80)
{'his': 80, 'eng': 70, 'chi': 60}

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屬性裝飾器

一般好的設計：把實例的屬性保護起來，不讓外部直接訪問

外部使用getter讀取屬性和setter方法設置屬性

class Person:
    def __init__(self, name, age=18):
        self.name = name
        self.__age = age

    def age(self):
        return self.__age

    def set_age(self, age):
        self.__age = age


tom = Person('tom')
print(tom.age())
tom.set_age(20)
print(tom.age())

out:
18
20

通過age和get_age方法操作屬性

有沒有更簡單的方式？

class Person:
    def __init__(self, name, age=18):
        self.name = name
        self.__age = age

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

    @age.setter
    def age(self, age):
        self.__age = age

    @age.deleter
    def age(self):
        del self.__age
        print('del')


tom = Person('tom')
print(tom.age)
tom.age = 41
print(tom.age)
del tom.age
# print(tom.age)


out:
18
41
del

另一種寫法：

class Person:
    def __init__(self, name, age=18):
        self.name = name
        self.__age = age

    def getage(self):
        return self.__age

    def setage(self, age):
        self.__age = age

    def delage(self):
        del self.__age
        print('del')

    age = property(getage, setage, delage)


tom = Person('tom')
print(tom.age)
tom.age = 41
print(tom.age)
del tom.age
# print(tom.age)

對象的銷燬：
 

類中可以定義__del__方法，稱爲析構函數

py實現了垃圾回收，這個方法不能確定何時執行，有必要時，請使用del語句刪除實例

class Person:
    def __init__(self, name, age=18):
        self.name = name
        self.__age = age

    def __del__(self):
        print('del le')


tom = Person('tom')
del tom