如何使用將名稱列表作爲參數的裝飾器將屬性添加到類中？

Question

我想通過一個裝飾了許多僞屬性添加到一個類，像這樣：

def addAttrs(attr_names): 
    def deco(cls): 
    for attr_name in attr_names: 
     def getAttr(self): 
     return getattr(self, "_" + attr_name) 
     def setAttr(self, value): 
     setattr(self, "_" + attr_name, value) 
     prop = property(getAttr, setAttr) 
     setattr(cls, attr_name, prop) 
     setattr(cls, "_" + attr_name, None) # Default value for that attribute 
    return cls 
    return deco 

@addAttrs(['x', 'y']) 
class MyClass(object): 
    pass 

不幸的是，decoarator似乎保持attr_name，而不是它的內容的參考。因此，MyClass.x和MyClass.y訪問都MyClass._y：

a = MyClass() 
a.x = 5 
print a._x, a._y 
>>> None, 5 
a.y = 8 
print a._x, a._y 
>>> None, 8 

我有什麼改變來獲得預期的行爲？

Answer 1

你幾乎有它的工作。只有一個尼特。當創建內部函數，的attr_name當前值綁定到獲取和設置功能：

def addAttrs(attr_names): 
    def deco(cls): 
    for attr_name in attr_names: 
     def getAttr(self, attr_name=attr_name): 
     return getattr(self, "_" + attr_name) 
     def setAttr(self, value, attr_name=attr_name): 
     setattr(self, "_" + attr_name, value) 
     prop = property(getAttr, setAttr) 
     setattr(cls, attr_name, prop) 
     setattr(cls, "_" + attr_name, None) # Default value for that attribute 
    return cls 
    return deco 

@addAttrs(['x', 'y']) 
class MyClass(object): 
    pass 

這產生了預期的結果：

>>> a = MyClass() 
>>> a.x = 5 
>>> print a._x, a._y 
5 None 
>>> a.y = 8 
>>> print a._x, a._y 
5 8 

希望這有助於。快樂的裝飾:-)

Answer 2

Python不支持塊級別範圍，只有功能級別。因此，循環內分配的任何變量都將作爲最後一個可用值在循環外部可用。爲了讓您正在尋找的結果，則需要在循環中使用閉包：

def addAttrs(attr_names): 
    def deco(cls): 
    for attr_name in attr_names: 
     def closure(attr): 
     def getAttr(self): 
      return getattr(self, "_" + attr) 
     def setAttr(self, value): 
      setattr(self, "_" + attr, value) 
     prop = property(getAttr, setAttr) 
     setattr(cls, attr, prop) 
     setattr(cls, "_" + attr, None) 
     closure(attr_name) 
    return cls 
    return deco 

使用封閉closure，內getAttr和setAttr將被正確作用域分配的屬性。

編輯：更正後的縮進