在Python中创建一个类实例属性只读

Question

我试图将一些模块包装到类中，并开始玩属性。

将这两个答案组合在一起：making instance attribute read-only和validating attributes。

我希望能够创造DataFolder类的一个实例：

df = DataFolder(owner="me", path="/.data") 

之后，我希望能够允许编辑owner属性，但不是path属性。我希望能够验证初始化时刻的属性（path和owner）以及之后（但仅owner）。

class DataFolder(object): 
    _path = None 

    #---------------------------------------------------------------------- 
    def __init__(self,owner,path): 
     self.path = path 
     self.owner = owner 

    @property 
    #---------------------------------------------------------------------- 
    def owner(self): 
     return self._owner 

    @owner.setter 
    #---------------------------------------------------------------------- 
    def owner(self,owner_value): 
     if "me" not in owner_value: 
      raise Exception("invalid owner") 
     self._owner = owner_value 

    @property 
    #---------------------------------------------------------------------- 
    def path(self): 
     return self._path 

    @path.setter 
    #---------------------------------------------------------------------- 
    def path(self,path_value): 
     if self._path is not None: 
      raise AttributeError("Cannot edit path of existing data folder") 
     if "dat" not in path_value: 
      raise Exception("invalid folder") 
     self._path = path_value 

它是正确的/最好使用全局变量_path = None和@path.setter检查if self._path is not None:？代码工作正常，但我想知道是否有更好的方法。

Answer 1

它看起来很好，除了一件事：_path = None属于一类。

这只是一个小的改良效果：

class DataFolder(object): 
    def __init__(self, owner, path): 
     self._path = None # now it is an instance variable. 
     self.path = path 
     self.owner = owner 

    @property 
    def owner(self): 
     return self._owner 

    def _validate_owner(self, owner_value): 
     if "me" not in owner_value: 
      raise ValueError("invalid owner") 

    @owner.setter 
    def owner(self, owner_value): 
     self._validate_owner(owner_value) 
     self._owner = owner_value 

    @property 
    def path(self): 
     return self._path 

    def _validate_path(self, path_value): 
     if self._path is not None: 
      raise AttributeError("Cannot edit path of existing data folder") 
     if "dat" not in path_value: 
      raise ValueError("invalid folder") 

    @path.setter 
    def path(self, path_value): 
     self._validate_path(path_value) 
     self._path = path_value 

使用：

d = DataFolder('me', 'data') 
print(d.path, d.owner) 
d.path = 'new_data' 

输出：

('data', 'me') 
new_me 
AttributeError: Cannot edit path of existing data folder