python父母子女關係課

Question

我寫了一個類，如下所示。我想將'父項'的屬性添加到我的基類節點。我想知道如果有人能告訴我如何正確地做到這一點。我已經得到了如何做到這一點的指導，但我並不完全確定如何寫出語法。這是建議的方式來做到這一點...

通常我會隱藏如此 其集時，前面的家長的孩子陣列可以被修改，從而 如果你說N A特性背後的父屬性。父= X，它實際上移除節點n從它的父 和設置父值

class Node(object): 
    def __init__(self, name, attributes, children): 
     self.name = name 
     self.attributes = attributes if attributes is not None else {} 
     self.children = children if children is not None else [] 


class Camera(Node): 
    def __init__(self, name="", attributes=None, children=None, enabled=True): 
     super(Camera, self).__init__(name=name, attributes=attributes, children=children) 
     self.enabled = enabled 

更新

import weakref 

class Node(object): 
    _parent = None 

    def __init__(self, name, attributes, children, parent): 
     self.name = name 
     self.attributes = attributes if attributes is not None else {} 
     self.children = children if children is not None else [] 
     self.parent = parent 

     for child in children: 
      child.parent = self 

    @property 
    def parent(self): 
     return self._parent() if self._parent is not None else None 

    @parent.setter 
    def parent(self, newparent): 
     oldparent = self.parent 

     if newparent is oldparent: 
      return 
     if oldparent is not None: 
      oldparent.children.remove(self) 
     if self not in newparent.children: 
      newparent.children.append(self) 
     self._parent = weakref.ref(newparent) if newparent is not None else None 


class Camera(Node): 
    def __init__(self, name="", attributes=None, children=None, enabled=True, parent=None): 
     super(Camera, self).__init__(name=name, attributes=attributes, children=children, parent=parent) 
     self.enabled = enabled 




Camera() 

Answer 1

實施例的代碼，結合weakref避免參考週期可以延遲清除（或防止它完全在某些情況下，particularly on Python 3.3 and earlier）：

import weakref 

class Node: 
# If this is Python 2, you need to explicitly inherit from object to 
# be a new-style class with descriptor support (which allows properties), so 
# the class line would be: 
# class Node(object): 
# On Py3, it's implicit and can be omitted 

    # Ensure attribute readable so getter/setter don't need to use has/getattr 
    # Will be allocated per-instance when self.parent is assigned in __init__ 
    # So on Py3.3+, it will still get the compact key-sharing dicts for attributes 
    _parent = None 

    # Adding defaults for all values matching Camera for simplicity 
    def __init__(self, name='', attributes=None, children=None, parent=None): 
     self.name = name 
     self.attributes = attributes if attributes is not None else {} 
     self.children = children if children is not None else [] 
     self.parent = parent 
     for child in children: 
      child.parent = self 

    @property 
    def parent(self): 
     return self._parent() if self._parent is not None else None 

    @parent.setter 
    def parent(self, newparent): 
     oldparent = self.parent 
     # If setting to existing parent, then no-op 
     # Remove this check and early-out if you want to be able to move 
     # a node to the end of its parent's children by reassigning the same parent 
     if newparent is oldparent: 
      return 
     if oldparent is not None: 
      oldparent.children.remove(self) 
     if self not in newparent.children: 
      newparent.children.append(self) 
     self._parent = weakref.ref(newparent) if newparent is not None else None 

通常，爲了避免與改變父類的原型的問題，我把附加首先參數到子類__init__方法，而不是最後一個。因爲我給了上Camera__init__違約，這使得Camera很簡單：

class Camera(Node): 
    def __init__(self, enabled=True, *args, **kwargs): 
     super().__init__(*args, **kwargs) 
     # On Py2, super isn't magic, so you need to be explicit unlike Py3: 
     # super(Camera, self).__init__(*args, **kwargs) 
     self.enabled = enabled 

正如你所看到的，由Camera獨特__init__ PARAM移動到前，Camera可以停止關注在Node__init__變化;新Camera作品與原Node或新Node（接受parent和分配self.parent）就好了，因爲它不太緊密耦合的確切參數排序。請注意，這意味着如果enabled未通過位置傳遞，則所有參數都必須通過關鍵字傳遞。

請評論，如果我犯任何錯誤，但應該是接近正確。一般來說，我有Node類使用parent訪問者通過正確處理None（None不是弱引用）來消除難度來簡化代碼。