超載Python類屬性的一種優雅的方式

Question

考慮一個基類：

class A(object): 
    def __init__(self, x): 
     self._x = x 

    def get_x(self): 
     #... 
     return self._x 

    def set_x(self, x): 
     #... 
     self._x = x 

    x = property(get_x, set_x) 

和派生類：

class B(A): 
    def set_x(self, x): 
     #... 
     self._x = x**2 

    x = property(A.get_x, set_x) 

是否有B類重載set_x()優雅的方式，無需再宣佈它和財產x？謝謝。

Answer 1

嘗試這一個：

class A(object): 
    def __init__(self): 
     self._x = 0 

    def get_x(self): 
     #... 
     return self._x 

    def set_x(self, x): 
     #... 
     self._x = x 

    x = property(get_x, lambda self,x : self.set_x(x)) 

class B(A): 
    def set_x(self, x): 
     #... 
     self._x = x**2 

由lambda給出的額外間接方法將使虛擬set_x函數成爲可能。

Answer 2

添加額外的間接層（即使用一個鉤子）：

class A(object): 
    def __init__(self, x): 
     self._x = x 

    # Using a _get_hook is not strictly necessary for your problem... 
    def _get_hook(self): 
     return self._x 
    def get_x(self): 
     return self._get_hook() 

    # By delegating `set_x` behavior to `_set_hook`, you make it possible 
    # to override `_set_hook` behavior in subclass B. 
    def _set_hook(self, x): 
     self._x=x 
    def set_x(self, x): 
     self._set_hook(x) 

    x = property(get_x, set_x) 

class B(A): 
    def _set_hook(self, x): 
     print('got here!') 
     self._x = x**2 

b=B(5) 
b.x=10 
# got here! 
print(b.x) 
# 100 

---

對於Python的現代版本，你也可以使用@property裝飾：

class A(object): 

    @property 
    def x(self): 
     return self._get_hook() 

    @x.setter 
    def x(self, x): 
     self._set_hook(x)