[问题解决] Python实现final这个功能

我不是女神ヾ 2022-01-17 03:29 116阅读 0赞

[为什么80%的码农都做不了架构师？>>> ][80_]  ![hot3.png][]

今天在学习设计模式的时候突发奇想，可不可以实现JAVA中的一些内容呢？

比如 final。

final在Java中是一个保留的关键字，可以声明成员变量、方法、类以及本地变量。一旦你将引用声明作final，你将不能改变这个引用了，编译器会检查代码，如果你试图将变量再次初始化的话，编译器会报编译错误。

## 修饰类 ##

当用final修饰一个类时，表明这个类不能被继承。

class Father(object):
        def __new__(cls, *args, **kwargs):
            if cls != Father:
                raise Exception('This class cannot be inherited.')
            return super(Father, cls).__new__(cls, *args, **kwargs)
    
        def __init__(self):
            print("Class Father")
    
    class Son(Father):
        def __init__(self):
            print('Class Son')
    
    if __name__ == '__main__':
        f = Father()
        s = Son()

运行结果：

E:\Anaconda\python.exe F:/PythonSpace/ClassMethod/test.py
    Class Father
    Traceback (most recent call last):
      File "F:/PythonSpace/ClassMethod/test.py", line 16, in <module>
        s = Son()
      File "F:/PythonSpace/ClassMethod/test.py", line 4, in __new__
        raise Exception('This class cannot be inherited.')
    Exception: This class cannot be inherited.

## 修饰方法 ##

明确禁止该方法在子类中被覆盖。

class Father(object):
        def __new__(cls, *args, **kwargs):
            if cls != Father and 'show' in cls.__dict__.keys():
                raise Exception('This method cannot be rewritten.')
            return super(Father, cls).__new__(cls, *args, **kwargs)
    
        def show(self):
            print("Class Father")
    
    class Son(Father):
        def show(self):  #删除后就不会报错
            pass
    
    if __name__ == '__main__':
        f = Father()
        f.show()
        s = Son()
        s.show()

运行结果：

E:\Anaconda\python.exe F:/PythonSpace/ClassMethod/test.py
    Traceback (most recent call last):
    Class Father
      File "F:/PythonSpace/ClassMethod/test.py", line 17, in <module>
        s = Son()
      File "F:/PythonSpace/ClassMethod/test.py", line 4, in __new__
        raise Exception('This method cannot be rewritten.')
    Exception: This method cannot be rewritten.

## 修饰变量 ##

对于一个final变量，其数值一旦在初始化之后便不能更改。

class Father(object):
        __final = 1
        def __setattr__(self, key, value):
            if key == '_Father__final':
                raise Exception('Property cannot be changed after initialization.')
            else:
                self.__dict__[key] = value
    
        def __init__(self):
            self.__final = 2
    
    
    if __name__ == '__main__':
        f = Father()

运行结果：

E:\Anaconda\python.exe F:/PythonSpace/ClassMethod/test.py
    Traceback (most recent call last):
      File "F:/PythonSpace/ClassMethod/test.py", line 14, in <module>
        f = Father()
      File "F:/PythonSpace/ClassMethod/test.py", line 10, in __init__
        self.__final = 2
      File "F:/PythonSpace/ClassMethod/test.py", line 5, in __setattr__
        raise Exception('Property cannot be changed after initialization.')
    Exception: Property cannot be changed after initialization.

## 结束语 ##

以上只是本人观点，难免有不足之处，只做参考，不做考究。

转载于:https://my.oschina.net/gain/blog/3001487

[80_]: https://my.oschina.net/u/2663968/blog/3051541
[hot3.png]: /images/20220117/cfdad4d773e64df198cf4843f4246930.png